Brettstapel An Investigation into the Properties and Merits of Brettstapel Construction
Brettstapel An Investigation into the Properties and Merits of Brettstapel Construction within the UK Market
James Henderson Supervised by Fiona Bradley Masters of Architecture Department of Architecture and Building Design Faculty of Engineering University of Strathclyde February 2009
Declaration I hereby declare that this dissertation is my own work, contains no unacknowledged text and has not been submitted in any previous context. All quotations have been distinguished by quotation marks and all sources of information, text, illustrations, etc. have been specifically acknowledged. I accept that if having signed this declaration my work should be found at examination to contain deliberate plagiarism the work will fail and I will be liable to face University discipline procedures.
19th January 2009
Acknowledgements I would like to acknowledge the advice and support given to me through-out this research by Fiona Bradley, my supervisor at Strathclyde University and Sam Foster of Gaia Architects. Together they have introduced me to Brettstapel and through Fionaâ€™s input encouragement and Samâ€™s enthusiasm and knowledge I have been motivated to conclude this work. I must recognise the award given to me by Jim Johnson and the Scottish Ecological Design Association that allowed me to travel to Austria and Switzerland to research Brettstapel in more detail. Thanks are also due to my boss, Jon Jewitt, for giving me the flexibility and advice necessary to hold down a job during this research and thanks also to everyone whose informal conversations have contributed in part to this work. Finally I would like thank my family and friends for keeping me sane through-out what has been the seventh, and hopefully last, year of my studies.
James Henderson January 2008
Abstract In 2006 a government review of the economics of climate change highlighted the effects of climate change on the developing world and in particular distinguished the massive contribution that carbon dioxide emissions make to this.
Since the publication was released the British
government decided to address the state of the changing climate and announced a series of carbon reduction targets including those to make all new developments, both domestic and non-domestic, carbon neutral by 2019. A large contributor to the carbon footprint of new buildings within the UK is the energy consumed by them and the material from which they are made. Timber is a significantly more efficient construction material than alternatives such as steel and concrete and importantly it locks in vast amounts of carbon dioxide from the atmosphere during its lifespan and therefore when used as a building material, it has negative embodied energy compared to carbon hungry alternatives. The UK has a large resource of timber which unfortunately due to its poorer quality, compared to Scandinavian and Canadian alternatives, is currently largely used to make fencing and packaging. It is however possible to utilise this timber within the UK construction industry in the form of massive timber construction systems, in particular Brettstapel. Brettstapel is one of the variants of massive timber construction utilising low grade timber to produce solid structural panels. It is made entirely from timber, including the connections and therefore it is devoid of toxic glues and nails which can have an affect on the well-being of building occupants. Brettstapel has been used in Austria, Switzerland and Germany since the 1970â€™s and has since evolved into a well refined structural system capable of rivalling traditional building techniques.
Surprisingly, prior to 2004
Brettstapel was largely unheard of in the United Kingdom. Initial studies have shown that Brettstapel could be used as an alternative building system within the UK due to its ease of fabrication, speed of erection and compatibility with low grade timber. It also provides a higher quality of building and has significant health benefits that would improve the quality of living with the UK. This document seeks to define the components and manufacturing process for Brettstapel, explain where it has evolved from, how it can be used and why we should specify and implement it within the UK market.
Table of Contents Page Number 0.0
Preface Title Page
Table of Contents
Table of Illustrations
Zero Carbon Construction
The UK Timber Industry
2.0 The Forestry Trade
2.1 Massive Timber
3.0 The History and Development of Brettstapel
3.1 The Manufacture of Brettstapel
3.3 On Site Erection
3.4 The Fit-Out
Brettstapel in Detail
4.1 Structural Possibilities
4.2 Environmental Benefits
4.3 Economic Implications
European Case Studies
5.1 S채gerei Sidler
Case Study: Acharacle Primary School
6.2 Environmental Strategies
7.1 The UK Construction Industry
7.2 Bringing Brettstapel to the UK
Appendix A. ECONO Project
List of Illustrations Figure
Description and Source
Breakdown of domestic carbon emissions (CLG 2007:8)
CO2 emissions from the manufacture of different materials (Wood for Good Limited 2003:5)
The carbon cycle of wood (Wood for Good Limited 2003:8)
Forest cover: international comparisons (Forestry Commission 2008:17)
Main tree species in UK (Forestry Commission 2008:12)
Distribution of UK woodland (Forestry Commission 2008:5)
UK consumption of wood 2007 (Forestry Commission 2008:67)
Distribution of sawn softwood in Scotland (Forestry Commission 2008:48)
BRE School in Watford by Eurban using the Leno construction system (www.eurban.co.uk)
A 7 storey Leno construction building being tested in Japan (www.eurban.co.uk)
Hotel Seiser Alm Urthaler in South Tyrol by Holz100 (www.thoma.at)
Hotel Seiser Alm Urthaler in South Tyrol by Holz100 (www.thoma.at)
24 Murraygrove in London by Waugh Thistleton Architects (www.waughthistleton.co.uk)
Professor Juilius Natterer (Natterer-bcn.com)
Nailed Brettstapel (Author’s sketch)
Horizontally dowelled Brettstapel (Author’s sketch)
Diagonally Doweled Brettstapel (Author’s sketch)
Map of known manufacturers (Author’s sketch)
Sitka spruce (www.forestry.gov.uk)
Douglas Fir Brettstapel (www.tschopp-holzbau.ch)
Maple and Walnut Brettstapel (www.tschopp-holzbau.ch)
The effects of timber harvested during the increasing lunar stages (Author’s photograph)
Timber stacked to dry out at Sidler sawmill (Author’s photograph)
Residential development by Sägerei Sidler near Zurich (www.sidler-holz.ch)
Community centre by Sohm in Blons, Austria (www.sohm-holzbau.at)
Interior view of Figure 24 showing industrial grade Brettstapel (www.sidler-holz.ch)
Brettstapel Profiles (Author’s sketch)
Brettstapel Profiles by Sohm (www.sohm-holzbau.at)
The milling process (Author’s photographs)
The biscuit joint (Author’s photographs)
Prefabricating a wall panel off site (www.kaufmann-holzbau.de)
Acharacle School: Laying the floor (Author’s photograph)
Acharacle School: Erecting the walls (Sam Foster’s photograph)
Acharacle School: Constructing the roof (Sam Foster’s photograph)
A typical covered wall section showing services running within the wall (Author’s photograph)
A void cut into a Holz100 panel to accommodate wiring (Author’s photograph)
E3 Flats, Berlin (www.e3berlin.de)
Doppelmayr Plant in Wolfurt, Austria by Sohm (www.sohm-holzbau.at)
Höfler Bridge in Riezlern, two 4m high x 17.5m long lateral trusses (www.sohm-holzbau.at)
Load versus span table (www.optiholz.ch translated by the Author)
Wall section with timber cladding (www.sohm-holzbau.at)
Wall section with render facade (www.sohm-holzbau.at
Ceiling/First Floor Construction (www.sohm-holzbau.at)
Cement Composite Floor Construction (www.sidler-holz.ch)
A burnt acoustic panel (www.sidler-holz.ch)
Sprinkler system being installed at Acharacle School (Author’s photograph)
Panels of Wood Fibre Insulation (Author’s photograph)
Section through a typical wall panel (Author’s photograph)
Acoustic Profiling between Posts (www.kaufmann-holzbau.de)
Sägerei Sidler’s new variant of an acoustic wall panel (Author’s photograph)
Holz100 built this house in 2 days (Author’s photograph)
Holz100 logo (www.thoma.at)
Cross section through external wall (Author’s photograph)
Cross section through two types of floor panel (Author’s photograph)
A timber effect aluminium window (Author’s photograph)
Solid Timber Beams supporting the first floor (Author’s photograph)
A burnt Holz100 panel, showing two layers burnt off (Author’s photograph)
The Erwin Thoma House (Author’s photograph)
The first floor bay windows (Author’s photograph)
Traditional external finishes- eaves detailing and copper guttering (Author’s photograph)
Internal view of house (www.thoma.at)
Construction of the Erwin Thoma House (Montgomerie’s photograph)
Fitting a single Holz100 panel (Montgomerie’s photograph)
Sägerei Sidler Logo (www.sidler-holz.ch)
The sawmill and production area (Author’s photograph)
The Brettstapel racking machine (Author’s photograph)
Completed Brettstapel panels (Author’s photograph)
The drilling and doweling machine (Author’s photograph)
The current residential project (www.sidler-holz.ch)
Internal view of Figure 103 during fit out (Author’s photograph)
A composite Brettstapel floor, prior to cement being poured (Author’s photograph)
Section through a composite floor (www.kaufmann-holzbau.de)
Collection of bark chips for use in wood chip boiler (Author’s photograph)
Storage of timber off-cuts to be used for paper production (Author’s photograph)
Artists Impression of Acharacle School (Courtesy of Gaia Architects)
Floor plan of Acharacle School (Courtesy of Gaia Architects)
The planned program for Acharacle Primary School (Courtesy of Gaia Architects)
The actual program for Acharacle Primary School (Courtesy of Gaia Architects)
South elevation of Acharacle School (Courtesy of Gaia Architects)
The classroom wing foundations (Authors Photograph)
(Author’s photograph) 82
Floor Construction Details [1:10] (Courtesy of Gaia Architects)
Wall plates fixed to foundations (Author’s photograph)
Fixing the floor panel to the base and adding insulation (Author’s photograph)
The ratchet used to pull floor panels together (Author’s photograph)
Sections cut out of floor panel for pop-ups (Author’s photograph)
Floor construction sequence (Author’s photographs)
Wall and Roof Details [1:10] (Courtesy of Gaia Architects)
The connection between an internal wall and floor panel (Author’s photograph)
The first wall to be erected, with temporary bracing (Author’s photograph)
An almost complete office within the school (Author’s photograph)
Sealant tape between sheathing boards (Author’s photograph)
The main hall, with sprinkler system in place (Author’s photograph)
Wall Construction Sequence (Sam Foster’s photographs)
Roof Construction Sequence (Sam Foster’s photographs)
Section through classroom (Courtesy of Gaia Architects)
Proposed internal views (Courtesy of Gaia Architects)
Pound verses Euro comparison (Author’s sketch sourced from www.xe.com)
Brettstapel is a massive timber construction system fabricated exclusively from softwood timber posts connected with hardwood timber dowels. James Henderson
Chapter 1 Zero Carbon Construction
1.0 Zero Carbon Construction The effects that climate change has on the developing world have been slowly brought to the publicâ€™s attention over recent years. Whilst many bodies have listened to the theories and arguments behind this, few have acted in an attempt to minimise the damage. Arguably the most significant report of the last decade on the subject of climate change was commissioned by the UK government in 2005. In 2006, The Stern Review on the Economics of Climate Change was published and proved that there was sufficient evidence to suggest that climate change was a significant threat to the developing world. It also highlighted that greenhouse gases, in particular carbon dioxide, were the biggest contributor to the current changing climate.
forecasts for the future are vague, the report showed that the financial cost of climate change was serious enough to warrant immediate action (Stern, 2006). The UK government promptly took action and after several notable bodies published further responses to the Stern Review, including one by the Department for Communities and Local Government (2007a), it issued a series of new targets to enforce a reduction in carbon dioxide levels. In 2004 the UK was responsible for producing in excess of 150 million tonnes of carbon dioxide.
Of these emissions, the energy consumed
within domestic buildings accounted for more than a quarter; almost 75% of that figure is the energy used to heat our homes (Figure 1) (Department for Communities and Local Government [CLG] 2007:8). The UK government pledged to reduce UK carbon emissions by 60% by the year 2050. Considering the high demand for housing, a three step plan was put in place by the UK government in 2007 to ensure that by 2016, all new housing developments meet zero carbon standards. This plan contained a series of reduction targets to improve the energy and carbon performance of current building standards by 25% by 2010. This target will increase to 44% by 2013 and then in 2016 it is hoped that all new buildings will be zero carbon (CLG 2007b:11).
later announced that in addition to the housing stock, all new nondomestic
(www.direct.gov.uk accessed December 2008).
water heating 20%
space heating 53%
Figure 1: breakdown of domestic carbon emissions (CLG 2007:8)
The UK construction industry now has the task of realising these targets and in doing so must seek to redefine the way in which buildings are constructed. One of the primary factors defining the carbon footprint of a building is the material from which it is constructed.
the atmosphere at a rate of 930 kilograms for every cubic metre of growth (Arnqvist et al. 2007:100). That is the equivalent to taking a car of the road for 4.5 months1.
Large amounts of carbon can
therefore become locked in the tree for the duration of its life and even
carbohydrates which release oxygen.
Through the process of photosynthesis this is then converted to
Steel (scrap based) 5.2
emissions (Figure 2). As trees grow, they absorb carbon dioxide from
sustainable product that the industry can use to reduce carbon
Steel (ore based) 19.3
By comparison with other building materials, timber is the most
when a tree has been harvested and used for building, paper or pulp, it still retains this sequestered carbon (Figure 3) (Wood. For Good Ltd. 2003:7,8).
Kgs of CO2 per square metre of building area Figure 2: CO2 emissions from the manufacture of different materials (Wood. For Good Limited 2003:5)
Figure 3: the carbon cycle of wood (Wood. For Good Limited 2003:8)
The average carbon dioxide emissions for new cars sold in 2005 was 169.4g/km; Average mileage for cars in 2005 was 8980 miles (14450km) (www.foe.co.uk, August 2008) Page 3
By increasing demand for timber in the building industry, more trees will be harvested which will encourage more new trees to be grown and more carbon to be sequestered. Because trees lock smaller volumes of carbon as they get older, planting young trees significantly reduces the amount of carbon dioxide in the atmosphere.
The Scottish forestry
sector is committed to contributing toward carbon saving targets; indeed a three stage proposal seeks to have annual savings of one million tonnes of carbon by 2020. This is to be achieved through reforestation, increased use of biomass and by substituting wood for more carbon hungry materials (Scottish Executive 2006:73). Specifying timber in building construction therefore will considerably help the government reach the zero carbon targets and increase the worldâ€™s carbon sink through sustainable forestry. Utilising Brettstapel will further increase these advantages as larger quantities of wood are used within buildings compared to timber frame construction. Brettstapel is generally clad with timber or left exposed which means that less masonry and metallic materials are used compared with timber framed buildings which are often finished with brick and plasterboard. Furthermore, the excellent thermal qualities of Brettstapel mean that there is less need for mechanical heating in a Brettstapel building. This is a crucial advantage as it means that and the total energy consumption is considerably less than that of a lightweight timber, brick, concrete and steel framed building.
In central Europe, where Brettstapel is most
prevalent, buildings are designed to conform to Passivhaus standards2. This achieves a 90% reduction in energy consumption compared to standard construction which means that Brettstapel significantly contributes to achieving the zero carbon goal. At the end of a buildingâ€™s lifecycle, it is important that as much of the materials as possible are recycled. Recycling Brettstapel continues the carbon sink of the timber thus maintaining a lower level of carbon dioxide in the atmosphere.
When timber can no longer be recycled,
burning it in place of fossil fuels, either in the form of an open fire or biomass plant, continues the positive effect it has on the environment. All these alternative uses mean that one piece of timber contributes a huge amount during its lifecycle to tackling the global issue of climate change.
Described further in Chapter 4.21 Page 4
Chapter 2 The UK Timber Industry
buildings however is rising, particularly in the housing sector, but the UK
is currently unable to meet the demand, relying heavily on imported
timber to sustain the high usage.
the long term effects this will have. The demand for timber framed
climate has temporarily slowed this growth and it is yet to be seen what
jobs and income than ever before. Unfortunately the current economic
The UK timber industry is a growing business, producing more wood,
1.0 The Forestry Trade
The UK has a lot less woodland than many other countries with a
coverage of just 11.6%. This is currently 18% less land area than the world average and almost 35% less than the European average (Figure 4) (Scottish Executive 2006:67).
The majority of UK timber that is
Figure 4: Forest cover: international comparisons (Forestry Commission 2008:17)
produced comes from Scotland and is predominantly low-grade softwood, most of which is Sitka spruce (Figure 5). Because of its grade strength (C16) and poorer quality, almost 65% is used for woodchips, fencing, packaging and sawdust (Forestry Commission 2008:48). These are all low cost products which do not make the most of current stock piles.
pine 17% other/mixed broadleaves 31%
Current statistics reveal that 17.1% (13,000km2) of Scotlandâ€™s land is covered by woodland, 47% of the UK total (Figure 6) (Scottish Executive. 2006:67). The Scottish Forestry Strategy Group wants to see this figure rise to 25% during the second half of the 21st century. This
spruce 33% oak 9%
other 4% larch 6%
will help achieve key targets namely improving the health and well being of communities, developing the Scottish economy and ensuring a highquality, adaptable environment. The Strategy also wishes to produce a
Figure 5: Main tree species in UK (Forestry Commission 2008:12)
consistent timber supply of 8.5million cubic metres each year (Scottish Executive. 2006:15). In 2007 the UK produced 9.1million green1 tonnes of softwood and 0.4million green tonnes of hardwood (Forestry Commission 2008:25).
54% of this softwood supply came from Scotland (Forestry Commission
northern ireland 3%
2008:47). Scotlandâ€™s efficiency at utilising timber increased in 2007 as Scottish sawmills only imported 6% of softwood therefore ensuring they scotland 47%
were gaining the maximum possible benefits from their crop.
Figure 6: Distribution of UK woodland (Forestry Commission 2008:5) 1
Green timber means freshly felled wet timber. The weight differs when dry. Page 6
metres of round wood it produced (Forestry Commission 2008:67).
limiting the return on it and minimising its value and contribution to the UK economy. The financial return from forestry is slowly increasing and between 2004 and 2007 was estimated to be around 22% per annum This was a vast improvement and
significantly made up for the negative figures seen as little as eight years ago.
A big financial gain to the economy in recent years had been
through employment. The increased demand for timber had meant that
30 20 10
The poorer quality of Scottish timber compared to other countries’ is
(Forestry Commission 2008:123).
wood products in 2007 (Figure 7), compared to the nine million cubic
consumption. The UK imported 54.1 million cubic metres of wood and
There is a massive shortfall however between timber production and
0 Figure 7: UK consumption of wood 2007 (Author’s sketch, sourced from Forestry Commission 2008:67)
the industry was able to support almost 10,700 jobs in forestry and primary wood processing industries in 1998/9. In 2007 1,343 persons were employed in large sawmills2 (1998/9 Forest Employment Survey, cited by Forestry Commission 2008:113).
Unfortunately due to the
current global financial crisis, these figures are significantly lower as demand for sawn wood for construction has greatly diminished along with all other construction products and services. In 2007 the UK produced 2,859,000 cubic metres of sawn wood and other 1%
2,764,000 tonnes of wood for other products, half of which came from Scotland’s forests. Unfortunately only 34% of the sawn wood was used for construction, with the remaining going into fencing and packaging (Figure 8) (Forestry Commission 2008:46,48).
Within the construction market, timber is mostly used on extensions to existing buildings, more so on residential than on any other building type. Whilst the majority of residential developments in the UK are still
being built with bricks and blocks, in Scotland, timber frame housing has a market share of 75%, considerably more than the national average of 22% (UKTFA 2008:17). This is dramatically below international figures which in most cases is approximately 80%. Indeed it was estimated in 2000, that timber frame accounted for 70% of all housing stock across all developed countries; in that year the UK average was 8% (Palmer 2000:2). Recently demand for commercial timber frame buildings has also risen: in 2008 there was a 28% increase in the market compared to the previous year (UKTFA 2008:17). 2
Large sawmill means a sawmill producing at least 10 thousand cubic metres of sawn wood and accounts for around 90% of all sawn softwood produced in the UK. Page 7
Figure 8: Distribution of sawn softwood in the UK (Forestry Commission 2008:48)
It is not unreasonable to think that as attitudes start to change and the industry becomes more aware of the social, financial and ecological benefits of timber, the UK as a whole could develop a healthier timber construction market. If the national average could be raised in line with Scotlandâ€™s share, the demand for timber could potentially rise from 180,000 to 250,000 cubic metres per year. This would significantly raise the value of the timber frame market (Davis Langdon Consultancy 2003:66), push for further development and innovation and increase the capacity of carbon sequestration with our forests. 2.1 Massive Timber Construction Massive Timber is the name given to construction methods that use solid timber elements.
Also referred to as Solid Timber Construction, this
method completely contrasts lightweight timber frame construction, where a frame, generally comprising of studs at 600mm centres, is infilled with an insulating material and clad with brick. In massive timber construction there is no framing method. Walls, floors and roofs are entirely made up of solid timber panels which are often load bearing. Solid timber construction is slowly becoming more popular within the industry in Europe as it allows complete buildings to be prefabricated
Figure 9: BRE School in Watford by Eurban using the Leno construction system (www.eurban.co.uk)
offsite and erected in short time periods. Massive timber elements also have excellent thermal and acoustic properties as well as being a very sustainable building method with good environmental credentials. There are several types of massive timber construction on the market which can be broken down into glued and non-glued versions. Examples of glued versions are glulam, paralam, Leno (distributed in the UK by Eurban) and some variants of Brettstapel. Non-glued systems include Brettstapel, Holz100 and the oldest system of all, log cabin construction.
Figure 10: A 7 storey Leno construction building being tested in Japan (www.eurban.co.uk)
Eurban have a large portfolio of massive timber buildings, many in the UK, using Leno Solid Wood Panels (Figure 9). This system comprises boards of pine, glued together crosswise in a minimum of three layers and is a product of Finnforrest Merk GmbH. Finnforest also manufacture other massive timber solutions including a non-load bearing wall system designed for internal walls. Leno panels have also been tested within a prototype seven storey timber building in Japan designed to cope with seismic activity (Figure 10) (www.eurban.co.uk accessed November Figure 11: Hotel Seiser Alm Urthaler in South Tyrol by Holz100 (www.thoma.at)
Holz100 claim to be the largest massive timber producer in Europe (Wachinger 2008). The Holz100 product consists of layers of timber laid horizontally, vertically and diagonally at 50 degree angles that are secured using a grid of dowels piercing the wood perpendicular to the panel. The firm recently set up a new branch in Norway and in 2009
Wood100 will be launched in Britain (Montgomerie 06.01.09).
currently export as far away as America and Japan but so far they have only built up to four storeys to date as the Austrian building standards which they are built to, do not permit a timber building to be constructed any higher. Their largest project, the Hotel Seiser Alm Urthaler (Figures 10 and 11), used enough wood to sequester 4,000 tons of carbon dioxide and by using Holz100 instead of bricks and concrete, prevented circa 6,000 tons of CO2 from being released into the atmosphere (www.thoma.at
Figure 12: Hotel Seiser Alm Urthaler in South Tyrol by Holz100 (www.thoma.at)
accessed December 2008). The tallest timber building in the world is currently The Stadthaus, 24 Murray Grove in London which stands at nine storeys high (Figure 13). It was designed by Waugh Thistleton Architects in collaboration with Techniker engineers and uses a similar system to Leno by KLH Massivholz based in Austria. The building is entirely made from timber including the lift cores, load-bearing walls and floor slabs and in 2008 won two “Wood Awards” for the Structure and Off-Site Construction categories (www.waughthistleton.co.uk accessed January 2009). The timber used within The Stadthaus sequesters a total of 181 tons of carbon and as with the Hotel Seiser above, it offsets a further 125 tons of carbon in avoiding carbon hungry materials (www.woodawards.com Figure 13: The Stadthaus in London by Waugh Thistleton Architects (www.waughthistleton.co.uk)
accessed January 2008) Prior to 24 Murray Grove’s completion, Kaden Klingbeil Architects successfully built Germany’s first seven storey timber building using glulam and Brettstapel supplied by Merkle. This was a small victory for timber construction as previously German building regulations had not permitted any timber structure over five storeys tall (www.e3berlin.de accessed January 2009).
Chapter 3 Brettstapel
3.0 The History and Development of Brettstapel Brettstapel was originally invented by the German engineer Julius Natterer in the 1970’s. It is a variation of massive timber construction and is widely used throughout central Europe today. Julius Natterer, (born 1938) graduated with a civil engineering degree from Munich in of the timber engineering field allowing him to acquire a comprehensive knowledge of timber construction methods. He founded his first company, Natterer GmbH in 1970 and since then has held several senior positions in his field, including the Chair of Timber Construction and Director of the Institute for Wood Structures at Lausanne University (Haller 2008:207).
Natterer is passionate about
innovation in timber construction and it is his belief that “only the use of wood in the construction field can save and renew the forests of the world…” (arch.usc.edu accessed November 2008).
Figure 14: Professor Julius Natterer (www.natterer-bcn.com)
The earliest form of Brettstapel consisted of posts of sawn timber laid side by side, continuously nailed together to create solid structural elements around 600mm wide. The thickness of the posts varied from 80-200mm allowing the long nails to penetrate 3-4 planks each (Figure 15) (Liddell 09.06.08). The nature of this product allowed for low grade timber to be used meaning that it was an affordable way of constructing solid, environmentally friendly structures.
Figure 15: Nailed Brettstapel (Author’s sketch)
The reason low grade timber could be used was because through human selection, knots and defects found in posts were never placed next to one another. One manufacturer, Zwick, claim that this system was once used to support mines and small railway passes in Germany (www.zwick-holzbau.de accessed August 2008).
This original form of
Brettstapel evolved to include the use of glues as a way of strengthening it thus enabling it to span longer distances. There were a number of disadvantages to this system however, particularly as problems arose when trying to modify elements - the randomly placed nails meant it was almost impossible to cut into the timber (Liddell 09.06.08). Despite the difficulties, Brettstapel was used in this original format until 1999 when Kaufmann Massiveholz GmbH developed the system known as Dübelholz (www.kaufmann-holzbau.de accessed August 2008).
Dübelholz, German for “wooden dowels” refers to the inclusion of wooden dowels which replaced the nails and/or glue of earlier systems. This innovation involved inserting hardwood dowels into pre-drilled holes perpendicular to the posts (Figure 16). Brettstapel could now be made Page 11
Figure 16: Horizontally dowelled Brettstapel (Author’s sketch)
entirely from solid timber with the potential to span up to 8 metres using panels 600mm wide and 80-300mm thick. This system was designed to utilise a moisture content variation between the posts and dowels. The posts were softwood (usually fir or spruce), and were dried to a moisture content of 12-15%. The dowels however were hardwood (mostly beech) and dried to a moisture content of 8%. When the two elements were combined together, the differing moisture content resulted in the dowels expanding to achieve moisture equilibrium and therefore ‘locking’ the posts together. The disadvantage of this system however was that in time contraction and expansion resulted in the timber posts separating slightly along the dowel thereby compromising the strength of Brettstapel.
addressed by reintroducing glue or nails between the posts.
resolved the issue of separation but meant that Brettstapel was no longer 100% timber. An Austrian company, Sohm HolzBautechnik GmbH decided to address this issue in an alternative way and patented their product, Diagonal
Dübelholz, in 2001 (www.sohm-holzbau.at accessed August 2008). Their innovative system inserted timber dowels at an angle through the posts in either ‘V’ or ‘W’ formations (Figure 17). This provided a more rigid jointing system which virtually eliminated the potential for movement gaps opening up between the posts, ensuring once again
Figure 17: Diagonally Doweled Brettstapel (Author’s sketch)
ensuring that Brettstapel could be a 100% timber product. Today, almost 20 companies are known to be manufacturing and using Brettstapel in Austria, Germany, Switzerland and more recently Norway (Figure 18).
Whilst most companies only build within fairly close
proximity to their factories, some are exporting as far as America. The most common form of Brettstapel today is the perpendicular dowel method with the majority of systems not utilising any glue. In addition, two companies are known to still use nails. Brettstapel is now finished to a wide variety of specifications that take into account individual aesthetic,
companies are continually striving to innovate and make their product a market leader.
Figure 18: Map of known manufacturers (Author’s sketch)
3.1 The Manufacture of Brettstapel The construction industry in Europe differs greatly from that in the UK. Companies involved in manufacturing Brettstapel have a lot of control over their product from the sourcing of timber to the completion of the construction and therefore immerse themselves in all aspects of the design and build process. These companies, however small, also act as engineer, architect, manufacturer and sometimes builder.
closely with their clients to design the output together and for individual projects they usually collaborate with an architect, although that is not always the case for mass build. The manufacture and prefabrication of the buildings is designed to their own standards and the process is completed by sending a firms own building team to construct the building. This is an excellent method of ensuring a high quality output. In the case of a speculative house building project, manufacturers design the houses, prefabricate them and then construct on site (Werner et al 2008). As a rule, they work on every stage of the building process, subcontracting only for the pouring of foundations and fit out of the building. This holistic design and build process allows manufacturers to design a building which exploits Brettstapel to its maximum potential whilst giving them complete control over the project. In the UK however, the approach to construction is very different and is one that involves many different parties in the production the final product.
Land owners, developers, engineers and architects are all
involved prior to commencement on site. The construction process is broken down into different skill bases, sub-contracting individual companies for the framework, faĂ§ade, roof erection and even the internal fit out.
This system inevitably leads to complex interfaces
between different organisations which can lead to errors compromising the quality of the final product. A major advantage of the European system is the short time in which buildings can be completed.
In Switzerland one company (SĂ¤gerei
Sidler) estimate it is a five week period from sawing dried timber through to finishing the prefabrication and fit out of a typical house (Werner et al 2008); Holz100 allow twelve weeks to design and build a house. A house can easily be put up in under a week and Holz100 have shown that it is possible to build a 2,300 square metre (25,000 square feet) shell in less than two days (Wachinger 2008).
3.11 Timber Selection and Processing The prefabrication process starts with the selection of a suitable timber. Softwoods are nearly always used for posts; Spruce and Fir are the preferred choice by most manufacturers mainly due to the fact that they grow quickly and abundantly in central Europe and are cheaper to purchase than other species.
Despite this, Larch, Douglas Fir, Pine,
Maple and Walnut have also been specified (www.tschopp-holzbau.ch accessed August 2008) and in some cases a mixture of these species are used, purely for aesthetic qualities (Figures 20, 21). In contrast, dowels are always made of hardwood and in most cases beech is the species of choice. The dowels are fundamental to the structural integrity of Brettstapel and have significant loads exerted on them during and after construction.
A softwood dowel which has a lower structural strength
would therefore not be feasible for this crucial connection role. One important factor relating to the use of long lengths of timber is the time of harvest.
Figure 19: Sitka spruce (www.forestry.gov.uk)
Harvesting during the decreasing lunar phases and
during the winter season produces trees of a higher density, that are much less prone to cracking and warping (Figure 22). This in part is due to the lack of sap flow during these periods. Because these logs also have less nutritional value, they are much less likely to be prone to
Figure 20: Douglas Fir Brettstapel (www.tschopp-holzbau.ch)
infestation (Thoma Holz n.d b and Wachinger 2008) and so strict guidelines to ensure correctly harvested timber is common amongst European timber manufactures. In addition to the structural integrity of timber being compromised when significant cracks appear, it is also deemed unsightly by companies that take a lot of pride in the appearance of their product.
Figure 21: Maple and Walnut Brettstapel (www.tschopp-holzbau.ch)
Before timber can be used in manufacture it must be dried to an appropriate moisture content. This is done either by leaving it to dry outside naturally (Figure 23) (depending on the climate this could take months or years) or alternatively it is dried in large kilns where it is finished to exact specifications. The general rule of thumb is that posts must have achieved 12 -15% moisture content and dowels should have achieved 8%. Sohm stipulate specific timber moisture content requirements depending on the final building typology: For a habitable room the recommendation is 12% ± 3%; for a room with low heating requirement it is 14% ± 3% and for an agricultural building 16% ±4% is recommended.
important that the moisture content is precise as a 1% variation will result in 0.01% change in length; a 0.20% change in width and a 0.30Page 14
Figure 22: The effects of timber harvested during the increasing lunar stages (Author’s photograph)
0.35% change in thickness. (www.sohm-holzbau.at accessed August 2008) Once the timber has reached the appropriate moisture content, it is ready for manufacture.
The timber will be cut to the required length1
and cross section and finished according to one of three quality grades dependant on how visible the final product will be.
The names and
conditions of each grade vary slightly from company to company but as a rule they can be summarised as Industrial (where Brettstapel is not visible), Standard (a basic finish for visible Brettstapel) and Exposed (a superior finish for where Brettstapel is fully visible). These are not strict
Figure 23: Timber stacked to dry out at Sidler sawmill (Authorâ€™s photograph)
grades and the manufacturer or client may specify otherwise on individual cases. 3.12 Specifying Brettstapel The industrial standard is more common in countries such as Switzerland, where Brettstapel is often covered (Figure 24,26), as opposed to Austria where Brettstapel is exposed as much as possible (Figure 25). The criterion of each grade is described below (www.sohmholzbau.at accessed August 2008):
Figure 24: Residential development by SĂ¤gerei Sidler near Zurich (www.sidler-holz.ch)
Industrial Grade: posts not planed or chamfered, colour stains and flaws permitted, knots and resin left untreated, small cracks conditionally allowed, unequal post widths acceptable. Standard Grade: posts planed and edges chamfered, colour variations conditionally allowed, cracks not permitted, knots admissible if less than 40mm in diameter, unequal post widths more controlled.
Figure 25: Community centre by Sohm in Blons, Austria (www.sohm-holzbau.at)
Exposed Grade: posts fully planed and chamfered, knots kept to absolute minimum, no discolouration permitted, no cracks or resin stains accepted, posts must be of equal width. Sohm also monitor the longitudinal curvature and rotation of posts in all grades. It must be less than 2mm in any direction for exposed grade Brettstapel whilst deviation of up to 8mm can be permitted for an industry grade post. Figure 26: Interior view of Figure 24 showing industrial grade Brettstapel (www.sidler-holz.ch) 1
The maximum length is often dictated by the size of doweling machine a company has and not by the maximum achievable span. Page 15
In addition to the grading criteria, Brettstapel can be modified to produce a variety of technical and aesthetic properties. The edges of posts are commonly chamfered or mitred in exposed Brettstapel to produce a greater aesthetic.
A common variation is to introduce
cylindrical voids behind the joint of each post to achieve superior acoustic qualities2.
Staggering the depth of alternative posts (see
plus/minus format below) in industrial grade Brettstapel can give more space to run services within walls (Figure 35).
Acoustic Profile 1
Staggered Posts (plus/minus)
Acoustic Profile 2
Figure 27: Brettstapel Profiles (Authorâ€™s sketch)
3.13 Manufacture and Tolerances Once posts are sawn and finished they are stacked on a dowelling machine which holds the posts together and drills holes through them. The holes generally have diameters 2mm less than the dowels which are then driven through them. In some cases the dowels are compressed further prior to use.
(For example a 22mm diameter dowel will be
compressed to 20mm and driven into an 18mm diameter hole.) A completed Brettstapel panel will expand slightly (approximately 5mm) when the clamps release and individual companies know what this expansion dimension is and therefore account for this in their design. The tolerance generally varies between 3.175mm (1/8th of an inch) and zero. SĂ¤gerei Sidler as a rule do not work with tolerances and will guarantee the exact dimensions of their product.
Figure 28: Brettstapel Profiles by Sohm
from left: Acoustic Profile; Shadow Gaps; Industrial Grade; (www.sohm-holzbau.at)
Described in more detail in Chapter 4.3 Page 16
3.131 The doweling process
1. The timber posts are stacked together and held in place
2. Any odd lengths are cut and defects sorted
Figure 29: The milling process (Author’s photographs) 3. The timber is fed through the machine
4. It is then drilled and dowels are forced into the holes
3.2 Prefabrication Whilst Brettstapel is a structural element, it is often produced as part of a prefabricated wall, ceiling or roof panel. The prefabrication starts with several completed sections of Brettstapel, generally made in panels between 400-600 millimetres wide. These are joined to each other using various methods, a common and simple one being a biscuit joint (Figure 30).
This consists simply of manufacturing each panel of Brettstapel
with a “groove” running down the length of each side, into which a single length of timber can inserted to join the sections together. Figure 30: The biscuit joint (Author’s photographs)
Once a large section of Brettstapel is formed, approximately four metres wide, it is built up to form the appropriate panel. For a wall panel, this may include a layer of plywood for racking strength, insulation and a vapour barrier. As the external layer determines a building’s appearance it can range from render, applied directly onto insulation, to timber cladding, hung from small battens. The façade however must be added in such a way as to maintain the moisture transmissivity of a wall. There is no constant formula to which a panel is made up and every company has their own variations. Generally companies will have more than one option for internal and external wall panels, floor/ceiling panels and roof panels. Some companies however specialise only in one type of panel, for example Sägerei Sidler predominantly produce floor panels.
Figure 31: Prefabricating a wall panel off site (www.kaufmann-holzbau.de)
Prefabricated panels must also include all the required structural openings and in many cases windows and doors are fitted into them during the manufacturing process.
This high level of prefabrication
helps to achieve air tightness around wall joints and structural openings because installing windows and doors off site means it is possible to achieve a greater degree of accuracy and a better fit between the two elements. This degree of prefabrication has huge benefits on site in that it greatly reduces the time spent erecting the superstructure. 3.3 On Site Erection
Figures 32-34: Progress at Acharacle School; laying the floor, erecting the walls and constructing the roof (Figure 32 – Author’s photograph Figures 33,34 – Sam Foster’s photographs)
In preparation for the installation, foundations are laid and wall plates screwed down into place along blockwork edges. The cranes used have to be able to take the large loads of the panels and the maximum size of crane available must be considered at the design stage. The first sets of panels to be laid are the floor panels.
dropped into place with a high degree of accuracy and speed and then fixed together.
Once the floor is laid down sole plates are installed
around the edges and onto these wall panels are secured. The shell continues to be put together in this way until a weather tight envelope is completed, ready for an internal fit out.
Figure 35: A typical covered wall section showing services running within the wall (Author’s photograph)
3.4 The Fit-Out The form of fit out has to be considered at the design stage.
ensures that pipes and wires can be concealed within a wall or floor during the construction process.
Where Brettstapel itself is to be
concealed, a “plus/minus” arrangement is often used (Figure 35) and in some cases, voids are designed into wall panels to allow services to be hidden (Figure 36).
Figure 36: A void cut into a Holz100 panel to accommodate wiring (Author’s photograph)
Chapter 4 Brettstapel in Detail
4.0 Introduction Brettstapel has been used in a wide range of projects including furniture, small houses, hotels and industrial buildings. In 2007, Germanyâ€™s first seven storey timber building, (nicknamed E3) was completed with the majority of wall and roof panels utilising Brettstapel construction (Figure 37). 4.1 Structural Possibilities Brettstapel is known for its ability to span long distances, making it ideally suited for large industrial buildings and for use in bridges. Currently companies can produce panels up to 12-15 metres in length, although not all of these can span that distance. Having studied all the different manufacturers, the most common distance to span is seven metres with the depth of Brettstapel required varying between 210mm and 250mm. Furthermore, spans in the region of thirteen metres are
Figure 37: E3 Flats, Berlin (www.e3berlin.de)
achievable when minimal loads are imposed on Brettstapel such as roof panels. Currently Brettstapel can only span longitudinally, unlike rival massive timber products which can span in two directions. However it does has great structural possibilities as Zwick Holzbau (www.zwickholzbau.de accessed August 2008) has stated that a length of Brettstapel 140mm thick can cantilever up to four metres unsupported. Brettstapel can also be used to make large truss formations which span much longer distances such as those required in large industrial units (Figure 38) and bridges (Figure 39). As the wood can be curved these can vary in form to suit different aesthetics.
Figure 38: Doppelmayr Plant in Wolfurt, Austria by Sohm (www.sohm-holzbau.at)
OptiholzÂŽ - Ceiling or roof element: Maximum applied load on panel (dead-load and live-load) in kN/m2 Maximum Deflection l / 350
net weight of Brettstapel is included Span (m)
2.00 2.20 2.40 2.60 2.80 3.00 3.20 3.40 3.60 3.80 4.00 4.20 4.40 4.60 4.80 5.00 5.20 5.40 5.60 5.80 6.00 6.20 6.40 6.60 6.80 7.00
50 mm 2.04 1.26 0.72 -
70 mm 7.36 5.22 3.73 2.67 1.88 1.30 0.85 -
90 mm 16.91 12.35 9.19 6.92 5.26 4.01 3.05 2.31 1.72 1.25 0.87 -
Brettstapel Width (mm) 110 mm 130 mm 150 mm 31.89 53.50 74.25 23.56 39.76 61.23 17.79 30.23 47.21 13.65 23.40 36.72 10.62 18.39 29.02 8.34 14.63 23.24 6.59 11.75 18.82 5.23 9.50 15.37 4.16 7.73 12.65 3.30 6.31 10.47 2.60 5.16 8.71 2.03 4.22 7.26 1.56 3.45 6.07 1.17 2.80 5.07 0.84 2.26 4.24 1.80 3.53 1.40 2.93 1.07 2.41 0.78 1.97 1.58 1.24 0.95 -
170 mm 95.48 78.76 66.05 54.17 42.96 34.54 28.10 23.08 19.12 15.95 13.38 11.28 9.54 8.09 6.88 5.85 4.97 4.22 3.57 3.00 2.52 2.09 1.71 1.38 1.08 0.82
190 mm 119.38 98.50 82.61 70.25 60.44 48.88 39.88 32.88 27.35 22.92 19.34 16.40 13.98 11.95 10.26 8.82 7.59 6.54 5.64 4.85 4.17 3.57 3.04 2.58 2.17 1.80
210 mm 138.95 120.44 101.03 85.93 73.95 64.28 54.47 45.01 37.55 31.57 26.73 22.76 19.49 16.76 14.46 12.52 10.87 9.45 8.23 7.17 6.24 5.44 4.73 4.10 3.54 3.05
Figure 39: HĂśfler Bridge in Riezlern, two 4m high x 17.5m long lateral trusses (www.sohm-holzbau.at)
Figure 40: Load v Span table (Optiholz 2007:2.3.2)
4.11 Panel Composition As stated previously, Brettstapel is usually only used on its own as an internal wall and is therefore often used as part of a prefabricated panel for external elements.
Each company has developed its own panel
typologies, ranging from thin sections of Brettstapel to 400mm wide panels ready for construction. Example 1: Exterior Wall with Timber Cladding (Sohm Holzbautechnik)
420mm wide; 0.24 W/m2K U-value; F60 fire rating 40mm Horizontal Timber Cladding 40mm Battens and Cavity 15mm Waterproof hardboard 180mm Wood Fibre Insulation 15mm Plywood 130mm Brettstapel Example 2: Exterior Wall with Rendered Façade (Sohm Holzbautechnik)
400mm wide; 0.22 W/m2K U-value; F60 fire rating Render Façade with Plaster Base 60mm Wood Fibre Insulation Vapour Barrier 240mm Brettstapel 15mm Plywood 80mm Brettstapel Example 3: Ceiling/First Floor Construction (Sohm Holzbautechnik) Carpet, Tile or Hardwood 15mm Plywood Floor Framing and Insulation Sound Matt Brettstapel From top:
Example 4: Cement Composite Floor Construction (Sägerei Sidler)
Figure 41: Wall section with timber cladding (www.sohm-holzbau.at)
Carpet Tile or Hardwood Plywood
Figure 42: Wall section with render facade (www.sohm-holzbau.at)
Figure 43: Ceiling/First Floor Construction (www.sohm-holzbau.at)
Concrete with embedded utility pipes Brettstapel
Figure 44: Cement Composite Floor Construction (www.sidler-holz.ch)
4.12 Fire Protection In addition to its structural properties, Brettstapel performs very well when subjected to immense heat or flames. This is due to the solid and air tight construction of the walls; a lack of air gaps means that no oxygen can flow through the walls which would otherwise aid the spread of fire.
This invariably means that Brettstapel burns slowly and
carbonises only on the surface. Brettstapel has received fire ratings of F30, F60 and in some cases F90. These ratings refer to the number of minutes that the panels can withstand fire without losing their load bearing capacity and are calculated in accordance with BS5268 sections 4.1 and 4.2: 1990. Sohm state that a 100mm thick panel achieves a 30 minute fire rating and a 120mm thick panel achieves a 60 minute fire rating (www.sohmholzbau.at accessed 2008).
Figure 45: A burnt acoustic panel (Optiholz 2007:4.1)
Completed wall and floor panels perform
similarly depending upon their make-up; again achieving ratings of F30 and F60. Interestingly, acoustic profiled Brettstapel burns quickly to the underside of the voids but then the fire will slow down causing the timber to char at the same rate as solid panels (Figure 45) (Optiholz 2007:4.1). â€œAn issue of relevance is that the surface spread of flame is not a significant issue on the continentâ€? (Halliday 2008:158). In order to be able to build with significant amounts of timber within the UK, strict fire safety methods must be employed to satisfy Building Standards. One way this can be achieved is by designing a sprinkler system into buildings which is activated through heat or smoke detection. Alternatively, the surface spread of flame can be addressed by coating the wood with an organic formula such as HR Prof. This is a clear water based fire retardant which does not contain any volatile organic compounds. It affects the colour of the wood very slightly and requires 1 litre per 3.7m2 of wall area (Bridgestock 2009). In order for the E3 building to pass German building regulations, (which had previously only permitted timber development up to five storeys in height) a high degree of fire safety measures had to be fully integrated into the design from inception. This resulted in shortened fire escape routes, high fire resistant construction and the careful sizing of load bearing components.
The ceilings were also coated in a clear flame
retardant and a greater level of smoke detectors was incorporated (www.e3berlin.de accessed December 2008). Page 22
Figure 46: Sprinkler system being installed at Acharacle School (Authorâ€™s photograph)
Fire tests on Holz100 panels which involved subjecting elements to temperatures of 1000 degrees Celsius for 3 hours only resulted in two layers of timber being burnt. Importantly, despite this loss of section, the panels still maintained their structural integrity.
The side not
exposed to fire only raised 2 degrees Celsius in temperature after exposure to fire for two hours (Thoma Holz n.d a:4). To ensure Brettstapel’s integrity as a construction material, it is frequently tested by European universities including Stuttgart, Vienna and Graz (Wachinger 2008). In Switzerland, testing is also performed by EMPA (Werner et al 2008), who specialise in the safety, reliability and sustainability of new construction materials. EMPA, which translates to
The Swiss Federal Laboratories for Materials Testing and Research, is part of ETH University in Zurich.
In testing Brettstapel they also
determine whether it conforms to international building regulations (www.empa.ch accessed October 2008). 4.2 Environmental Benefits It is often assumed that building with timber constitutes an “environmentally friendly and sustainable” construction method.
true that the use of timber within buildings has a much less damaging impact on the environment than concrete, brick or steel but these elements are still often found within a timber frame building.
superstructure of a Brettstapel building however can potentially be 100% timber. 4.21 Indoor Air Quality The exclusion of glue and nails in massive timber construction, combined with exposed, untreated timber helps to produce a good healthy indoor air quality because timber absorbs potentially harmful volatile organic compounds (V.O.C.’s) in the atmosphere. By creating a healthy indoor environment free from V.O.C.’s, the health and well being of the occupants is significantly increased. Using doweled Brettstapel naturally achieves this indoor environment, provided that its surfaces are not coated with impervious toxic finishes. If the dowelled systems are not used one square metre of Brettstapel, 160mm wide and 40mm thick will have a surface area of four square metres requiring glue. Alternatively the same panel size would require approximately 400 nails (www.longin.at accessed October 2008).
A healthy environment is further enhanced when specifying Brettstapel due to the hygroscopic nature of the construction method.
naturally hygroscopic, meaning that moisture can easily pass through a timber structure without condensing between layers. This is particularly useful in keeping the indoor humidity levels down, which a study by a Canadian university has proved has a significant effect on occupant comfort, perceived air quality, occupant health, building durability, material emissions and energy consumption. This study showed that a hygroscopic building structure reduced the peak indoor humidity by up to 35% RH and increased the minimum indoor humidity by up to 15% RH (Simonson 2003:2).
Building with Brettstapel also avoids the need
for “wet trades” on site, i.e. plasterers and so reduces further reduces the risk of damp and mould developing internally. In order to maintain the quality of indoor environment provided by timber, it is common practice to use wood fibre insulation alongside Brettstapel (Figure 47). The low thermal conductivity (0.038W/mK) maintains a low U-value in wall or roof panels and its hygroscopic properties allow for complete breathable construction. Wood fibre can be made from 95% waste timber (www.natural-building.co.uk accessed December 2008) and subsequently does not emit V.O.C.’s.
contributes to the carbon sink of a building. Figure 47: Panels of Wood Fibre Insulation (Author’s photograph)
Other insulations that may also be considered for use with Brettstapel are Hemp and Sheep wool, both of which offer similar advantages to wood fibre. They have thermal conductivity ratings of 0.040 W/mK and 0.038W/mK respectively and are both hygroscopic. Interestingly using 1kg of hemp insulation instead of glass wool will save 1.4kg of Carbon Dioxide.
An advantage of sheep wool is that it does not burn and
instead melts, thus not compromising the fire performance of a structural panel (www.natural-building.co.uk accessed December 2008). The quality of air inside Brettstapel buildings, whilst dramatically improved by the abundance of wood, can be further improved by specifying certain species of timber.
Arolla Pine (Pinus Cembra) is
currently being used by Holz100 to make massive timber panels in bedrooms as it has a distinct scent, not dissimilar to lavender, which infuses the air around it.
It has been proven by Professors at the
Joanneum Research Society that living, and especially sleeping in this environment has a positive effect on your mental and physical well being (www.thoma.at accessed December 2008) and could therefore slow your
heart by up to 3500 beats a day, the equivalent to an hour of cardio vascular workout (www.zirbe.info accessed October 2008). As well being able to produce a healthy environment, it is possible to build an air-tight building using Brettstapel construction, something that is very rare with other construction methods. Air gaps around structural openings and poor wall/ceiling joints can lead to unwanted drafts which can make it difficult to control the energy losses in buildings whilst maintaining comfortable ventilation and air flow.
Air tightness is
something that BRE and Passivhaus standards both take into account when calculating the energy rating of a building. 4.22 Passivhaus Design In the countries where Brettstapel is prevalent, it is frequently being used to build Passivhaus standard buildings.
Passivhaus is a set of
German derived construction standards that can be applied to residential, commercial and industrial buildings.
standards are predominantly used in central Europe, there are many examples of their world wide implementation; there are however very few examples in the UK. Buildings that conform to Passivhaus make good use of solar and internal heat gains thus minimising the required heating load. This is achieved with well insulated buildings that are air-tight, have minimal thermal bridges and are verified by a registered officer at the design stage of a project. A typical Passivhaus building uses 90% less energy than other comparable designs. A house is deemed to be Passivhaus if the total
energy demand for space heating and cooling is less than 15 kWh/m2/yr treated floor area; and the total primary energy use for all appliances, domestic hot water and space heating and cooling is less than 120kWh/m2/yr (www.passivhaus.org.uk accessed November 2008).
4.23 Thermal Performance Timber as a building product has excellent thermal conductivity compared to materials such as steel (50 W/mK), lightweight concrete (0.38 W/mK) and plasterboard (0.16 W/mK). Brettstapel has a thermal conductivity of 0.13 W/mK. As stated previously, one of these panels will generally consist of Brettstapel, insulation and external cladding (Figure 48). The panels manufactured by Sohm Holzbautechnik achieve U-values between 0.12 and 0.24 W/m2K. These values are well below current Building Standards which specify a minimum U-value of 0.30 W/m2K for wall construction. As with all massive timber systems, Brettstapel has an excellent thermal mass which inadvertently can be used as a natural way of maintaining a comfortable indoor temperature.
Holz100 have performed tests to
demonstrate this: three rooms were built in a controlled environment
Figure 48: Section through a typical wall panel (Author’s photograph)
with an outside temperature of -10 degrees Celsius and an indoor temperature of +21 degrees Celsius. The heating was turned off and the time was measured for the internal surfaces to reach zero degrees Celsius.
The results showed that timber frame construction (U-value
0.16 W/m2K) took only 50 hours to cool down and brick construction (Uvalue 0.34 W/m2K) took nearly 100 (Thoma Holz n.d. a:7). The massive timber wall however only reached zero degrees Celsius after 225 hours. This proves the excellent heat storing abilities of massive timber Figure 49: Acoustic Profiling between Posts (www.kaufmann-holzbau.de)
construction systems. 4.24 Acoustic Perfomance A further advantage of Brettstapel is that it can be altered to improve acoustic properties. By introducing small absorption and reverberation voids behind the joints of each post (Figure 49), acoustic performance is dramatically enhanced. Air-borne sound travels up these voids thereby reducing reverberation within buildings.
In Switzerland, it is not
uncommon to see boundary walls and fences with acoustic, noise deflecting qualities, particularly when houses are situated close to a road. Sägerei Sidler has developed a new variant of Brettstapel that has further improved acoustic properties.
Using angled timber posts in a
“saw tooth” arrangement with acoustic insulation between (Figure 50), they are able to deflect sounds waves within the outer edges of a panel and absorb them before they reach the inner face. They anticipate that these panels could be used either as fences or as external walls. Figure 50: Sägerei Sidler’s new variant of an acoustic wall panel (Author’s photograph)
4.3 Economic Implications There are many factors to consider when determining how cost effective Brettstapel construction is.
Whilst the cost of 1 square metre of
Brettstapel is more expensive when compared to lightweight timber or brick construction, there are many savings to be made in the process of designing and building.
The performance of Brettstapel is also
considerably higher than other systems which results in much lower running costs post completion. 4.31 Material Costs In December 2008, the price of constructing a three bedroom house in Scotland in both lightweight timber frame and Brettstapel forms of construction was calculated and compared. Working with an Austrian manufacturer, it was determined that the cost of the superstructure would be 20% higher if built with Brettstapel, (this does not account for transportation costs) (Foster 07.01.09). This estimate was confirmed by another massive timber supplier in Scotland who in costing several projects during 2008 estimated that the cost of using massive timber would be 20-25% more than that of lightweight timber during 20071 (Montgomerie 06.09.09). In breaking down the pricing of the house, the cost of the Brettstapel panels (i.e. including plywood, wood fibre insulation, sheathing board and vapour barrier) required for the external walls (230m2) was £100,000, compared to the cost of the timber frame which was £65,000 (Foster 07.01.09).
Per square meter of construction, this equates to
£434 for Brettstapel and £282 for timber frame.
Due to the changing relationship between the pound and euro at the time of writing, this percentage will vary considerably in time. Page 27
Furthermore, the cost of massive timber as a single element (i.e. without insulation and sheathing board etc.) can be broken down, per square metre, as follows:
These costs relate to 80mm and 240mm Brettstapel and 120mm and 306mm Holz100. Although the material costs are high, what one must consider in judging the cost of Brettstapel is the time it takes to pre-fabricate and erect a Brettstapel building as well as the reduced post occupancy costs due to its energy efficiency and air tightness. 4.32 Construction Costs It takes SĂ¤gerei Sidler approximately five weeks to construct a four bedroom house, from sawing the timber to completing the fit out; the majority of this time being spent prefabricating the panels. It is actually possible to put the shell of a house up in two days, using a workforce of two to four people (Figure 51). A discussion with a Scottish house builder (Campbell 2009) revealed that it is possible to erect a standard timber frame (i.e. ground floor, first floor and roof trusses) of a four bedroom house in a day to a day and a half, with approximately four men. It will however, take a further two weeks clad this with brick, requiring a total of nine to twelve weeks to completely finish the house. This comparison shows that whilst the erection time is comparable, a Brettstapel house can be fully finished in a quicker time period. Additional expense may be incurred in the cost of crane hire during erection; Brettstapel is considerably heavier therefore requiring a larger crane. This can be avoided by reducing the size of the prefabricated panels - this will however have time implications.
Prices correct as of January 2009 (Gerber [Email] 2009) Prices correct as of January 2009 (Montgomerie [Email] 2009) Page 28
Figure 51: Holz100 built this house in 2 days (Authorâ€™s photograph)
4.33 Post Completion Savings Once a building has been fitted out, real savings start to be realised almost immediately, with the initial savings predominantly being seen in energy bills.
Due to the quality of the construction system, the
achievable air tightness, the high thermal mass and quality of insulation, the amount of energy required to heat a house is significantly reduced. This can be further reduced by making use of solar and thermal gains. These benefits can also be applied to larger commercial buildings, and in part to industrial buildings.
As a Brettstapel building is built for
longevity, i.e. in excess of 100 years, these savings will remain constant for the lifespan of the house. If Brettstapel can be more widely used for residential projects in the UK then these savings will have a direct effect on the country’s carbon emissions, due to the fact that the energy required to heat residential buildings equates to 14% of the UK’s total carbon emissions (CLG 2007a:8). 4.34 Set-Up Costs In order to bring the price of Brettstapel down in the UK, it would be necessary to manufacture it in the UK. A small sawmiller the size of Sägerei Sidler, which has an output capacity of 12,000 square metres of Brettstapel per annum, equating to approximately 70 houses, (Werner et al 2008) could be an ideal size for a “start up” business. It would be possible to increase this two-fold using the same machinery, should the demand arise, through longer working days and more staff. A larger manufacturer would be more comparable to Holz100, who have a current output of 200 houses per annum from a 4,000 square metre factory.
Again it is believed this output could be doubled with the
existing plant resources to accommodate any increase in demand for Brettstapel (Wachinger 2008). Whilst much of the machinery required to prepare timber for Brettstapel is found within a standard sawmill, bespoke machinery is required to drill and dowel the timber. This machinery costs in the region of £500,000 (Werner et al 2008), however second hand machines have been seen on the market and one sold in 2005 for £100,000 (Liddell 14.07.08) whilst another was put on the market in 2007 (www.fordaq.com August December 2008).
Taking into account the cost of machinery and start up costs, should a Brettstapel production line be started in the UK it would be more financially beneficial to extend an existing sawmill rather than create a brand new one. This would also enable the sawmill to generate income through other projects and not rely on Brettstapel as a sole income until the industry can generate enough projects.
Chapter 5 European Case Studies
5.0 Holz100 In order to get a better understanding of how Brettstapel is made and used, I was fortunate to have the opportunity to visit two manufacturers in Europe and to see examples of it in use (this was facilitated by a travel grant from the Scottish Ecological Design Association, SEDA.)
Figure 52: Holz100 logo (www.thoma.at)
Trying to contact Brettstapel manufacturers proved harder than expected, not least due to the language barrier and this in itself proves how little demand there currently is for this product out with the four producing countries. I received positive communication however from several companies including Sohm Holzbautechnik, Sägerei Sidler and Holz100. My first visit was to Holz100 in Goldegg, south of Strasbourg. I felt it was necessary to see an alternative massive timber product to conventional Brettstapel in order to better understand the market and be
Figure 53: Cross section through external wall (Author’s photograph)
able to compare the advantages of different forms of massive timber. Holz100 differs from Brettstapel in that it comprises of layers of timber, laid horizontally, vertically and diagonally at 50 degree angles. These are secured using a grid of dowels piercing the wood perpendicular to the panel to create panels between 12mm and 30.6mm thick. Holz100 has been in production since 1996 and is one of the few companies to export their product; they recently also opened up a production line in Norway using Norwegian timber. They claim to be the
Figure 54: Cross section through two types of floor panel (Author’s photograph)
largest manufacturer of massive timber in Europe, employing 180 people over three sites and currently have an output of 200 houses annually. Holz100 has a wide client base, constructing buildings in residential, commercial, industrial, health, education and even religious sectors. It has also sold a licence to a Scottish company who are currently setting up a UK outlet. The firm is actively pursuing their first project in the UK and have been quietly generating interest in their product. Holz100 panels can be produced as large as 3x8m and can span in two directions, as opposed to the single span of Brettstapel. Holz100 can guarantee no movement in panels post production and make them accurate to 3.2mm (1/8th of an inch) tolerances.
manufacture window and door fittings, using either aluminium (Figure 55) or timber frames which are fitted during the prefabrication. They have the skills to finish buildings to suit both traditional (Figure 56) and
Figure 55: A timber effect aluminium window (Author’s photograph)
modern aesthetics which has enabled them to build up an extensive portfolio of works with varying client bases. Environmentally, Holz100 claim to have to the lowest U-value of any structural system and only ever use wood fibre insulation so as to maintain pure timber buildings.
They can build with most species of
wood however spruce and pine are the most accessible and commonly used timbers.
As with Brettstapel, dowels are always Beech and the
cladding is most often Larch.
All timber used is specified to be
harvested during the decreasing lunar stages or during the winter. One square metre of Holz100 takes between four and five hours to
Figure 56: A burnt Holz100 panel, showing two layers burnt off (Author’s photograph)
make; previously when this was done by hand it took sixteen hours. This construction time is significantly longer than a Brettstapel section which takes around ten minutes to construct. Holz100 panels cost between 108 Euros for a square metre of 120mm thick panel and 242 Euros for a square metre 306mm panel (Montgomerie 07.01.09). As with all massive timber construction, Holz100 has excellent fire ratings; a completed element can withstand temperatures of 1000 degrees for 150 minutes without loosing its structural integrity (Figure Figure 57: Solid Timber Beams supporting the first floor (Author’s photograph)
56) (Thoma Holz, n.d. a:4).
5.01 The Erwin Thoma House
Figure 58: The Erwin Thoma House (Author’s photograph)
In order to see Holz100 in use, I was taken to the site of a current project, a house for Mr Erwin Thoma, the owner and founder of the company. The prefabricated panels were erected in a similar way to Brettstapel, connected to the foundations via timber wall plates. Solid timber beams and columns (Figure 57) were used in conjunction with the Holz100 to enable longer spans.
Inspecting these I was able to
naturally confirm through inspection the lunar harvesting theory. They
Figure 59: The first floor bay windows (Author’s photograph)
had mistakenly used wrongly harvested timber in one room and cracks that were clearly evident in the columns did not appear anywhere else on site. The use of solid timber columns and beams meant that large openings were easily achievable, bringing in lots of natural light and the breathtaking views of the Austrian landscape. The house incorporated the local traditional copper guttering and roof finish (Figure 60) and had an in-situ concrete basement. Apart from these elements the house was entirely timber. It took Holz100 approximately twelve weeks to design
Figure 60: Traditional external finisheseaves detailing and copper guttering (Author’s photograph)
and construct a similar house; however this house is almost being treated as a side project and due to its scale was programmed to take longer to finish. The triumph of the house for me was the master bedroom suite which used Holz100 made from Arolla Pine.
As mentioned previously, this
scented pine has an incredibly soothing aroma and proved to be very a pleasant and relaxing environment to stand within. The feeling when you stepped into the house was overwhelming; it is hard to describe how or why but the smell and appearance of the timber had a very calming effect. You could feel nature embracing you in this building – much in the same way as the building embraces the natural qualities of wood. Figure 61: Internal view of house (www.thoma.at)
Figure 62: Construction of the Erwin Thoma House (Montgomerie’s photograph)
Figure 63: Fitting a single Holz100 panel (Montgomerie’s photograph)
5.1 Sägerei Sidler My second visit was to the Sidler Sawmills, (Sägerei Sidler AG) south of Zurich in a small village called Oberlunkhofen.
I had received very
positive communication from them and considered them to be an ideal case study for transferring back to Scotland. Sägerei Sidler is a small Brettstapel manufacturer with 9 staff
Figure 64: Sägerei Sidler Logo (www.sidler-holz.ch)
(www.sidler-holz.ch accessed August 2008). They specialise in ceiling and floor panels and are capable of working on every part of the construction process themselves, from accepting taking delivery of green timber to fitting out houses.
This sawmill sits on 0.65 hectares (1.6
acres) of land and includes a sawmill, construction shed, storage, seeping tanks, biomass plant and an administration block. It is a good example of what could be needed to start up a plant in Scotland considering Sidler has an output of 12,000 square metres of Brettstapel a year, approximately 70 houses.
Presently they are able to
Figure 65: The sawmill and production area (Author’s photograph)
manufacture Brettstapel up to 11.5 metres long, however with the imminent arrival of new machinery this will soon increase to 15 metres. Sägerei Sidler manufactures the more common horizontally doweled Brettstapel which contains no glue or nails. The firm is however working on developing new forms of Brettstapel and were able to coincide the first run of a new acoustic panel with my visit, guiding me through the complete manufacturing process. I was shown the milling process which turns the trees into posts and then witnessed these posts being made into a Brettstapel panel. From here I was able to see it being built up into a wall panel. The panels were being prepared to be sent for testing to the Swiss research institution, EMPA, who test them against all the necessary criteria in order for them to pass Swiss building standards. Figure 66: Brettstapel racking machine (Author’s photograph)
Figure 67: Completed Brettstapel panels (Author’s photograph)
Figure 68: The drilling and doweling machine (Author’s photograph)
5.11 Site Visits Throughout the course of the day at SĂ¤gerei Sidler, I visited examples of houses that they have worked on.
Firstly I was shown a new
development of houses, completely built with Brettstapel and solid timber (Figures 69, 70). The sawmill had worked on every part of this development including erection and so had had complete control over the final output. The first thing that struck me about this development was that no timber was exposed: I was told that the Swiss generally want their buildings to
Figure 69: The current residential project (www.sidler-holz.ch)
look expensive and sleek and Brettstapel does not conform to this ideal. This does not stop them specifying it however as they are well aware of its advantageous qualities. It is questionable how much impact covering Brettstapel in plasterboard and render has on its qualities.
The health benefits alone must be
greatly diminished, whilst the environmental and financial benefits must also be reduced. This is in complete contrast to the Austrian examples I saw where timber is exposed as much as much possible, if not completely. One advantage to covering Brettstapel however is that the lowest grade timber can be used and no finishing is required. This has
Figure 70: Internal view of Figure 103 during fit out (Authorâ€™s photograph)
cost and time benefits that can start to balance out the equation. The second site I visited was another housing project, but this time only the ceiling and floor slabs were Brettstapel (Figure 71). It is common in the Swiss building industry to construct houses with bricks and mortar and to have a solid timber floor. Here Brettstapel is used for its ability to span long distances as well as for its acoustic and heat properties. The Brettstapel used in this case had staggered posts so that under floor heating could be installed and a thin concrete screed could be poured on top. Essentially this was a timber/concrete composite floor panel (Figure 72). The roof in this house was also solid timber and again this would not be exposed.
Figure 71: A composite Brettstapel floor, prior to cement being poured (Authorâ€™s photograph)
Figure 72: Section through a composite floor (www.kaufmann-holzbau.de)
Despite using concrete with some of their products and covering the majority of it up, Sidler are aware of their impact on the environment and do their best to maintain a low carbon footprint; this is achieved by using 100% of every tree: Bark is combined with off-cuts and burnt on site in a wood chip boiler (Figure 73) producing heat and energy for the whole site and for sixteen surrounding houses. Excess timber from this process is also used in pulp production. In addition, any lengths of timber that are not thick enough for Brettstapel are taken away daily to be used for paper production (Figure 74). In this way, the company ensure they get a maximum return on the timber they buy and at the
Figure 73: Collection of bark chips for use in wood chip boiler (Authorâ€™s photograph)
same time are able to power themselves with clean, renewable energy thus reducing the embodied energy of their product.
Figure 74: Storage of timber off-cuts to be used for paper production (Authorâ€™s photograph)
Chapter 7 Conclusions
7.0 Introduction Brettstapel presents many positive opportunities to the UK on a social, financial and environmental level. Socially, it offers a low cost solution to providing a good quality of housing that could raise the standard of living in the UK. Using Brettstapel can offer a significant boost to the UK construction and forestry industries and subsequently to the national economy.
It will also help to meet the governments zero carbon
housing targets and forestry targets, thus helping the country to meet and surpass its Kyoto commitments. In order for any of the above ideals to be realistic achievements, significant quantities of Brettstapel need to be produced and used throughout the UK. Through examination of the European case studies it has been shown that a relatively small sawmill is easily capable of producing in the region of 70 houses a year. It is unlikely that there would be demand enough for this in the first year, or even in the first five years of UK production, however with increased exposure and positive marketing this could soon become a realistic annual target. 7.1 The UK Construction Industry â€œBrettstapel has already made the transition from a peripheral enquiry on the part of ecological designers to a cost effective, elegant, benign material...â€? (Halliday 2008:142) The future of Brettstapel will however ultimately be determined by the amount of demand for it by all parties concerned in the construction industry, ranging from private clients through to local governments.
For these parties to want to specify
Brettstapel they need to be informed and convinced of its merits, in particular of its financial return.
It is unfortunate that the British
construction industry is so profoundly concerned with the cost, rather than quality of a building. This is a contrast to other European countries who value health, quality and whole life cycle performance in as high regard as cost.
The UK market is so restrictive at present that a price
difference of 1% is still considered a project winning margin (Campbell 2009). This could be the reason the UK timber construction industry is behind its European counterparts; the cost of building with brick and timber frame has been reduced so significantly by the influx of highly efficient volume house builders, that it is almost financially implausible for them to consider any other method. On the other hand however, exists the continued public demand for a generic, high volume output; this does
appear to be changing however as the demand for bespoke private housing is rising. Private house builders are driven by current legislation which presently does not include any specific quality standards and so they will not experiment with new technology or raise their standards unless ultimately the law makes them.
Ironically this is a contrast to the
legislation in place for social housing which demands a higher quality of building and spatial planning compared to the private sector: Social housing could therefore be a potential market for Brettstapel in the UK. The benefit Brettstapel also brings to a Housing Association is the low running costs post construction, something that is of little to no concern to high volume house builders (Campbell 2009). 7.2 Bringing Brettstapel to the UK â€œOne way forward is to import Brettstapel and other massive timber panel types directly from European and Scandinavian sources in order to gain direct experiences of the construction and design realities in the Scottish situationâ€? (Planterose 2007). Many of the questions preventing Brettstapel being used in the UK will be answered with the steady growth of suitable British precedents, because with these comes precise data on cost, construction, social and environmental impact; the school at Acharacle may prove to be a catalytic project and interested parties will eagerly await the outcome of the post occupancy evaluation in 2010. Precedents are slowly emerging in Scotland with schools and private houses leading the way.
Massive timber projects are also emerging
which whilst not specifically Brettstapel, also raise awareness of the materials benefits within the industry. It is likely that the private house type will dominate this market initially, at least until significant interest has been developed to make it otherwise. Unfortunately as these early precedents are realised, they will inevitably be built in association with European companies, utilising their timber, resources and labour and will therefore not be as much benefit to the UK as they should be. This will not change until UK Sitka spruce is tested in Brettstapel panels and can pass British certification and regulations. This should become a much simpler process when the British Standards become superseded by the European Codes in 2010 - Brettstapel currently conforms to Eurocode 5. (www.eurocodes.co.uk accessed January 2008). This would be an innovative use of Sitka spruce within a
UK sawmill and would also stop the construction industry being so reliant on exported timber. 7.21 Testing Brettstapel In order to test UK timber within a Brettstapel panel, the simplest way will be to identify a European manufacturer to whom Sitka spruce can be shipped and who will then this to construct Brettstapel panels. Throughout the course of this thesis, potential partners have been identified but the next step will be to get an institution in Britain to test the samples for conformity to British Standards and Regulations. These facilities do already exist at many universities and moves are currently been made to test Holz100 at a Scottish university.
are in line with how Brettstapel is tested on the continent: Universities in Graz, Vienna, Munich and Stuttgart have all participated in testing for massive timber and so knowledge may be gained through liaising with these institutions. 7.22 Developing a Market Should all the testing prove that it is technically feasible to produce UK Brettstapel successful (during the course of this research no explicit reason as to why it would not be has emerged) it will be possible to start manufacturing Brettstapel in Britain. This may be achieved in a variety of ways, the most productive method perhaps being through a consortium consisting of a sawmiller, housing association and architect. This would ideally work by expanding the existing facilities of a sawmill by purchasing the specialist plant necessary to manufacture Brettstapel. Inevitably this would require considerable investment, however by extending an existing sawmill, as apposed to creating a new one, a significant amount of unnecessary expenditure could be saved and the payback period of plant would be much less. By working closely with a housing association a small market could immediately exist within the UK; Brettstapel meets the demands of these associations more so than those of volume house builders who are reluctant to embrace innovation.
The biggest advantage of using a
housing association as an outlet is the ability to build multiple dwellings at one site as this will have initial financial benefits to complement the life cycle savings of the buildings. Involving an architect in developing a UK market is essential to be able to realise the full design potential of Brettstapel and get as much from it as possible in terms of energy savings. Page 61
The key to physically building Brettstapel buildings within the UK will be to train a British work force to construct a Brettstapel building to the same high standards as seen on the continent. This could be achieved by collaborating with a European company to train experienced builders and carpenters either on a British or European construction site. It has been suggested that due to the simplicity of Brettstapel, completing one build would be sufficient experience (Werner et al 2008). There are other ways of setting up Brettstapel production in the UK. The option does exist for an entirely new Brettstapel manufacturer to set up from scratch, however this would be extremely costly and the payback period could be very long.
Alternatively Sohm Holzbautechnik
have previously unsuccessfully attempted to sell a licence to a Welsh based company, effectively creating a franchise as Holz100 have done in Scotland.
A technology transfer agreement was in place as was the
offer to train a team to manufacture and erect Brettstapel (Burns 05.08.08). Whilst this was unsuccessful, it is a promising situation and shows European manufacturers are willing to expand and share their technology in the UK. Brettstapel is not a new technology; it is just new to the UK. It has already proved to be successful and versatile in Europe and there is no reason why this method of building can not be transferred to the UK. 7.3 Summary Brettstapel can be used to construct domestic, industrial and commercial timber buildings that have excellent environmental, insulating, aesthetic and energy efficiency advantages. Unlike timber frame construction, Brettstapel can span up to fifteen metres, sustain higher applied loadings and has great diversity as a construction material (Bradley 2008).
The ability to prefabricate buildings offsite and erect them
quickly is an added advantage to the construction industry, especially within the poor British climate, whilst the increased use of UK timber will have huge ecological benefits to the global environment and to the UK economy. Ultimately specifying Brettstapel within the UK construction industry will contribute towards a higher quality of construction; a higher standard of living; an improved environment and towards the increased health and well-being of future occupants.
Chapter 6 Case Study: Acharacle Primary School
Figure 75: Artists Impression of Acharacle School (Courtesy of Gaia Architects)
Client: Highland Council Architect: Gaia Architects Engineer: Sohm Holzbautechnik and Fairhurst Consulting Construction Time: January 2008 â€“ March 2009 Project Value: ÂŁ5.6million The first building to be constructed in the UK using Brettstapel is Acharacle Primary School. Situated on the north-west coast of Scotland, the school is being built to replace a collection of buildings that were no longer deemed suitable. The client, Highland Council, appointed Gaia Architects firstly to write the brief in April 2004 and then again in January 2005 to design the school. The building was originally designed as a traditionally built timber frame construction, but after receiving high tender returns, the architects suggested that Brettstapel might be a more cost effective alternative. This was a natural suggestion for Gaia after their earlier involvement in the European research project, Econo1, which had brought this method of construction to their attention.
For the many reasons discussed
earlier in this document, the client agreed to further investigation. The client and design team took a study trip to the Vorarlberg region of Austria where they were shown Brettstapel projects and manufacturers. After experiencing the product first hand and subsequently receiving more favourable tenders, the client agreed to adopt it in the Acharacle School. In ideal circumstances, the Brettstapel would have been manufactured in Scotland using local timber.
This could have involved one of two
scenarios, either setting up a Scottish outlet and buying bespoke
Refer to Appendix A for further information on the Econo project. Page 39
machinery to create an entirely new sawmill or, finding a sawmiller with the expertise, facilities and machinery necessary to manufacture it. The first scenario was recognised as being an unrealistic target given the cost and time involved.
The second scenario was considered more
feasible but after investigation was also deemed unachievable because no sawmillers had the specialist machinery required to manufacture it. To produce it manually would have had significant time and cost implications. It was decided that the most feasible option would be to have an international firm manufacture Brettstapel using imported Scottish timber and Gaia Architects had already made contact with several manufactures through the field trip. After finding a company that were happy to work on the project, Gaia Architects were disappointed to learn that they could not use Scottish timber. This was due to the fact that Scottish timber had not been specifically tested for use in Brettstapel and therefore it did not conform to any building regulations or construction quality standards. Sohm Holzbautechnik were appointed to the project in 2007.
appointment was made possible through the help of an Austrian Architect, Walter Unterainer, who had considerable experience with Brettstapel and had worked with this company during the course of his career.
The contract used was a JCT 98 contract with nominated sub-
contractors for the substructure and fit-out. Sohmâ€˜s appointment involved very little changes to the design of the school; this was mainly due to the versatility and structural capabilities of Brettstapel.
The original timber frame design remained virtually
unaltered meaning that the previously attained planning permission did not need amended.
The drawings required to develop the tender
package were drawn specifically for the timber superstructure by Gaia, with help from Walter Unterainner. All the details for this were drawn at 1:2 and 1:5 scales thus ensuring the architects had an excellent understanding of the construction. The technical details were calculated and drawn by Sohm who were able to send over the necessary data for Fairhurst Consulting engineers to issue a SER certificate for building warrant (this did however come in German and required translation). During the application for a building warrant, the two main issues Building Control were most concerned with were the surface spread of flame and the integrity of the structure under fire.
The first was Page 40
addressed through the addition of a suitable sprinkler system (see 5.13) meaning no potentially toxic coatings needed to be applied to the wood. The second concern was quickly resolved as Brettstapel panels already had a certified fire rating of F30, which was high enough to satisfy Building Control that the integrity of the structure would be sufficient. 6.1 Construction Construction was planned to be delivered in seven stages: substructure; community wing superstructure and fit out; entrance hall superstructure and fit out and classroom wing superstructure and fit out.
phase was scheduled to last five weeks and the remaining stages were scheduled to last a total of 48 weeks (Figures 77, 78).
Figure 76: Floor plan of Acharacle School (Courtesy of Gaia Architects)
Whilst the first and last phases were completed by local contractors, the erection of the floors, walls and roof was done completed by Sohm. Employing European labour was a significant feature of the project, having implications to both the cost and time. The cost was inevitably affected by having to accommodate the 9 Sohm labourers for three months but this was offset by speed they brought to the construction. It would not have been possible for British labourers to construct the structure as quickly with the same size of team - mainly due to their lack of experience with Brettstapel. By employing the Austrians a generally accepted superior service and higher quality of workmanship was brought to the project.
An initial program (Figure 77) was planned to increase efficiency during the build but unfortunately this was not adhered to.
Instead of each
phase being completed by Sohm and handed over to the subcontractors, the superstructure panels were erected, the mechanical and electrical fit out was started (so that services could be installed within partitions and floors) and then Sohm completed the internal linings for decoration by the subcontractors (Figure 78). This caused some logistical issues in terms of the programme which could have been reduced by integrating more of the services into the elements during prefabrication (Foster 07.01.09).
Figure 77: The planned program for Acharacle Primary School (Courtesy of Gaia Architects)
Figure 78: The actual program for Acharacle Primary School (Courtesy of Gaia Architects)
Despite only one of the Austrian work force being able to speak fluent English, the language barrier was not as problematic as one might have suspected. This was in part due to the organisation and hierarchy of the work force. crane
Even the need for frequent communication between the
unproblematic as the majority of it was done by commonly understood hand signals. The main problem that had to be overcome was the Austrianâ€™s relaxed attitude towards British health and safety standards which are not as Page 42
strictly enforced on the continent. During the early weeks of the project the site agent and clerk of works had to explain to them the high British standards for site health and safety â€“ fortunately they were quick learners and willingly complied. All the panels were manufactured in a nine week period in Austria and shipped over on standard articulated trucks.
Considerable time was
spent planning the haulage routes which meant that there were no special requirements: the trucks were able to use the same roads as standard logging haulage trucks which meant the remote location of the site was never a problem to deliver to. 6.11 Foundations On site, the foundations were laid by the appointed contractors, McGregor Construction who were responsible for the substructure of the School.
Mass excavation of the land was carried out to achieve the
desired footprint. As the new school had been designed to allow for the existing school to remain in use throughout the construction period, the site designated for the new build was on a slope.
This meant the
ground floor slabs needed to be stepped to minimise the amount of excavation required (Figure 79).
The foundations for the school comprised 800mm wide and 200mm
Figure 80: The classroom wing foundations (Authors Photograph)
Figure 79: South elevation of Acharacle School
deep concrete strip foundations, onto which was laid a double skin of blockwork, in-filled with a general concrete mix. Air bricks were placed at 1800 intervals in the top course of the blockwork for solum ventilation and the ground was filled with compacted hardcore up to the base of the upper course of blockwork (Figure 81). Once the foundations were laid the first stage of the build was completed allowing the Austrian work force to commence with their section of the superstructure construction.
Figure 81: Foundation detailing (Authorâ€™s photograph)
Figure 82: Floor Construction Details [1:10] (Courtesy of Gaia Architects) 6.12 Phase 2: Floor Structure Page 44
Almost 100 floor panels were completely manufactured in Austria to British building standards. Their size was influenced by the restrictions in the factory where they made and by the size of truck that they could be transported in. The weight of each panel was also dictated by the crane being used in the factory and on site. The floor is built up with three layers: the “first fix”, the prefabricated airtight panels; the “second fix”, additional insulation and support for; the “third fix”, the final floor finish (Figure 82). The first two layers are
Figure 83: Wall plates fixed to foundations (Author’s photograph)
consistent throughout the build whilst the floor finish varies throughout. The floor panels are filled with cellulose insulation prior to installation to increase the U-value of the floor. In preparation for the delivery of the floor panels, timber wall plates were secured with 12mm threaded rod to the blockwork (Figure 83). The wall plates were 2 lengths of timber, 60mm deep and 230mm wide and of varying lengths imported from Austria at the request of Sohm. They come in lengths of up to 12m long. Although this length is not easily achieved with Scottish timber, smaller lengths would not have affected the design - they would merely have increased the amount of
Figure 84: The ratchet used to pull floor panels together (Author’s photograph)
labour involved and therefore proportionally the time taken to lay them. 6.121 Floor Installation The floor panels arrived on large haulage trucks and were immediately unloaded onto the awaiting substructure. This operation was executed in an extremely efficient manner, with every member of the team working on one floor panel. The panels were guided into position by hand and then forcefully connected with a ratchet (Figure 84), thus ensuring that the workforce worked to the smallest of tolerances. The panels were then screwed at pre-marked points that corresponded to the foundations and wall plates below. Before the next panel was laid,
Figure 85: Fixing the floor panel to the base and adding insulation (Author’s photograph)
50mm of mineral fibre insulation was stapled to the side of the preceding panel to avoided cold bridging (Figure 85). Where pop-ups/service holes were involved, the relevant floor panels had sections incorporated into them that lined up precisely with pop-ups on site. There were supplied with timber covers to later conceal them (Figure 86). One floor panel took approximately 5 minutes to lift into place and secure. As each section of floor was laid, it was promptly covered with a heavy duty bituminous membrane until the walls were ready to be put up. 6.122 Floor Construction Sequence Page 45
Figure 86: Sections cut out of floor panel for pop-ups (Author’s photograph)
1. Panel is attached to the crane…
2. and lifted over the foundations
3. Pop-ups are fed through before…
4. panel is lowered into place
5. Panel is levered into position or…
6. hammered into position
7. A ratchet forces panels closer together
8. The Panel is screwed to wall plates
9. Mineral fibre is stapled to each side
10. It is covered with heavy membrane
Figures 87-96: Floor construction sequence (Author’s photographs)
Figure 97: Wall and Roof Details [1:10] (Courtesy of Gaia Architects) Page 47
6.13 Phase 3: Walls and Roof The longest and most labour intensive phase of the build was the erection of the walls and roof.
Again this was completed by the
Austrian workforce and a local crane operator. The walls arrived as prefabricated panels - the primary element within them was 100mm thick Brettstapel, made up with 60x100mm spruce posts joined by diagonal beech dowels. The Brettstapel, which forms the internal surface through-out most of the school2, is the only load bearing element of the wall panels. Ironically it is considerably smaller than studs used to frame out the insulation. The internal walls of the
Figure 98: The connection between an internal wall and floor panel (Author’s photograph)
school vary between single leafs of Brettstapel to full panels, similar to the external. The walls are secured to the floor panels with 160x60mm timber sole plates. During the erection the wall panels were temporarily braced until complete rooms are erected and structurally stable (Figure 99). Most of the panels were pre-fabricated with smaller windows and frames in place, however the larger glazing panels were installed after erection to minimise damage.
The glazing was all prefabricated in Austria by
Sohm’s nominated sub-contractor and installed by Sohm on site. Behind all the Brettstapel is wood-fibre insulation. This was originally specified as Warmcell insulation but Sohm suggested this change as they
Figure 99: The first wall to be erected, with temporary bracing (Author’s photograph)
often use it with Brettstapel construction and were aware of the benefits it would bring to the school without incurring a cost increase. Crucially, due to its hygroscopic nature wood-fibre enables a complete breathing wall construction to be fabricated which allows indoor moisture to be drawn through the walls to the outer face (Foster 07.01.09). The 280mm of insulation required in the walls to achieve a U-value of 0.125 W/m2K is sandwiched between fir based plywood and sheathing board. This meant that 280mm studs were necessary to support tie th e structure together.
This does make the section slightly confusing to
view as it appears that these studs, almost three times as thick as Brettstapel, are the structural element. Figure 100: An almost complete office within the school (Author’s photograph)
In some cases, boards are to be mounted at eye level so that work may be pinned onto the wall without damaging Brettstapel. Page 48
In order to obtain the air tight values specified in the design, Sohm used a sealant tape between all the joints on the external face of the sheathing boards (Figure 101). The prefabricated panels themselves are completely air tight and the superstructure is calculated to have an air permeability index (API) of 0.27m3/hr/m2@50Pa, which falls within the targets set for Passivhaus standards. The external finish for the school is a horizontal larch cladding, sourced and manufactured locally and is secured on to walls with 40mm battens. The larch is finished with organic paints of varying colours, a theme continued throughout the school.
Figure 101: Sealant tape between sheathing boards (Author’s photograph)
The colours were chosen by a
specialist consultant to “evoke differing feelings, increase stimulation and aid learning within the building” (Foster 07.01.09). Due to the fact that timber is exposed almost entirely throughout the school it was necessary to install a robust sprinkler system to pass fire safety standards. The Brettstapel itself has a 30 minute fire rating and as previously mentioned, because it is a solid and air tight structure it only chars on the surface. However, the sprinklers avoid the need to coat the surface with a fire resistant material to reduce the surface spread of flame thus satisfying British Building Standards. The Brettstapel structure within the roof panels varies in depth between 140-220mm; it is also given a variety of finishes to suit different uses. In the class rooms the Brettstapel has been given an acoustic finish and elsewhere a 4mm shadow gap has been incorporated between the posts
Figure 102: The main hall, with sprinkler system in place (Author’s photograph)
for an alternative aesthetic appearance. The build up above the Brettstapel in the roof again includes 280mm of wood fibre insulation between timber joists.
Between the Brettstapel
and insulation layer is a vapour barrier, above which sits the copper roof on 100mm battens.
The copper theme has been continued into the
rainwater pipes, referencing traditional Austria building methods. The school does make use of the wet climate in Acharacle by collecting the rainwater for reuse in the toilets. This is one of many energy saving features designed into the school.
Figure 34: Constructing the roof (Sam Foster’s photograph)
6.131 Wall Erection Sequence
1. Wall panels are erected one by one
2. Temporary bracing supports each wall
3. High level windows are fitted above
4. Outer walls of the hall are erected
5. Interior partition walls are attached to craneâ€Ś
6. and lifted into place
7. (left) interior Brettstapel walls are fitted 8. (above) All interior walls are in-place ready for the roof construction. Figures 103-110: Wall Construction Sequence (Sam Fosterâ€™s photographs)
6.132 Roof Erection Sequence
1. Brettstapel panels are craned into place
2. The deck the roof is laid and…
3. the panels are screwed down.
4. Roof light panels are added separately…
5…and placed above the corridors.
6. Wiring is laid ahead of the M&E fit-out
7. The roof is made water tight…
8. Before the copper is ready to be cut
Figures 111-120: Roof Construction Sequence (Sam Foster’s photographs)
9. The copper roof is cut and laid in-situe
10. The school nearing completion in 2009 Page 51
6.2 Environmental Strategies The school has been designed from the outset to include a variety of environmental strategies to reduce the running costs and improve the efficiency of the school. Of all these measures, the one that has been most prominent is the heating strategy. Although the school has been designed in accordance with Passivhaus standards it will not achieve official recognition as it does not have mechanical heat recovery system, currently a requirement for all Passivhaus design3.
The school however is predicted to only need
approximately half an hour heating on cold mornings to pre-heat the rooms before the pupils come in. The school will then be heated using the internal heat gains from the pupils, staff and electrical equipment as well as using solar gains. This method of heating has caused the school to be dubbed â€œthe Weetabix Schoolâ€? because essentially the energy consumed by children eating their breakfast will be responsible for heating it. By using Brettstapelâ€™s inherent moisture buffering capability and high thermal mass it is possible to reduce high temperature and moisture swings throughout the daily cycle within the school.
Figure 121: Section through classroom (Courtesy of Gaia Architects)
Whilst heating the school is complemented by the careful utilization of internal gains, a high tech solution has been employed for the cooling system to aid natural ventilation.
Each room has been fitted with
sensors to monitor the heat, carbon dioxide and humidity levels and if any of these exceed comfortable working conditions, the windows will automatically open: Low windows will let cool air in, whilst high windows opposite will draw warm air out (Figure 121). The windows will all have a manual override to ensure the user has full control of the environment.
When complete, the schools energy performance will be tested and monitored over a two year period. It is believed that it will achieve full Passivhaus targets, which if realised, will question the need for mechanical ventilation to be written into the Passivhaus requirements. Page 52
Furthermore, the school has been orientated to allow for south facing glazing in the principally occupied spaces, maximising solar gain. North facing glazing has been reduced to minimise heat loss. In order to meet the power requirements, the school will have a small wind turbine on site. This should meet all the demand for energy to heat the school as well as most of the demand for lighting. It is expected that the school will only require 7,000 kilowatt hours from the national grid per year (Foster 05.12.08). As well as all these energy saving features, health has been put at the forefront of the design where air quality is concerned.
structure and insulation is almost 100% timber, the design has reduced the levels of volatile organic compound gases to as close to zero as is possible. Taking into account the hygroscopic qualities of the structure and the natural ventilation strategies, the air quality will be of the highest possible standard, ensuring a safe and healthy indoor working environment.
Figures 122-125: Proposed internal views (Courtesy of Gaia Architects)
6.3 Acharacle Conclusions There is a lot of expectation riding on the new school. Its success will be measured on many levels: how it functions as a school; how it measures against the original budget and time scale and how much energy it consumes. A fundamental question will also be the merits of the decision to use Brettstapel. The answers to all of these questions, except the first, will ultimately have a significant impact on the future of Brettstapel buildings within the UK. The initial cost and delivery time of any building project is arguably the primary concern of a large majority of clients, contractors and investors in Britain today. It is often these factors that have the largest bearing on any project, and in many cases the design and quality can detrimentally suffer.
In the case of Acharacle Primary School,
Brettstapel was initially significantly cheaper than timber frame and did have a shorter associated construction period. The client was also able to understand the long term cost and health benefits of using Brettstapel and in doing so took a slight risk to use this innovative system previously unproven in the UK. 6.31 Acharacle Costs There are several factors that have all had a significant bearing on the final cost of the project, which has risen since the start of the school. Initially, the it would have cost more had it been built with a timber frame system and would not have performed as well in the long term. The final cost of the school however has been negatively affected by the need to import Brettstapel from abroad. At the start of the design process it became apparent that the Brettstapel would need to be manufactured and imported from Austria thus incurring a cost increase. Many clients might have reversed their decision to utilise Brettstapel at this point, but this client and the
1.6 1.4 1.2
architect were adequately convinced of its many merits that they
continued to pursue it. Notably, at this point in the project the price
difference incurred was not excessive.
the distance the Brettstapel needed to travel by truck. Unfortunately (or Page 54
9 Ja n0
(Figure 126). The cost of oil also contributed to a price increase due to
against the euro was indeed responsible for a 25% rise in project cost
problems in recent months the unprecedented crash of the pound
Although this has been blamed for many
global financial situation.
Unfortunately, a significant price rise did occur due to the deteriorating
Figures 126: Pound verses Euro comparison (Authorâ€™s sketch sourced from www.xe.com)
fortunately depending on one’s point of view) these cost increases both became apparent very late into the project and so the price rises had to be accepted by the client.
Fortunately there was a big enough
contingency fund to prevent the project from being halted. 6.32 Time Scale The project time scale was positively affected both by the decision to use Brettstapel and the need for Austrian builders to construct it. The speed at which the Brettstapel was erected and the precision and discipline of the Austrian work force ensured this short build time was strictly adhered to. Overall the project was designed to take 52 weeks, although it is expected to finish 12 weeks behind schedule. The prefabricated panels allowed for the majority of work to be continued without delay in wet weather however because of the need for a crane, adverse wind did have an affect on the program. Moreover, in Acharacle the religious faith of the village meant that “permission” had to be sought from the Church elders before the construction team could work on Sundays to make up for any lost time. 6.33 Energy Costs In order to understand how efficient the energy usage in the school will be, it will be monitored for two years after completion.
primary school of Acharacle's size would consume 80,000 kilowatt hours of fuel for heating but the engineers working on the school initially estimated that the fuel consumption will only be approximately 10,000 kilowatt hours due to its energy saving design features. In the case of lighting requirements engineers estimate that the school will use 10,700 kilowatt hours of electricity compared with a similar sized school that would use 18,700 kilowatt hours.
Considering the power
generated by the wind turbine will be 13,700 kilowatt hours, Acharacle school is “predicted to need only 7,000 kilowatt hours of power compared to 98,700 for a similar traditionally built school” (Foster 05.12.08). As well as reducing the amount of energy required to run the building, the school will have a very desirable affect on the climate in terms of the sequestration of carbon.
The school has used approximately 1,100
kilograms of wood which has therefore locked in a total of 1,025,790 kilograms of carbon dioxide (Foster 16.01.09).
6.34 Construction As far as the structure goes, Brettstapel has been able to be used in the same way as timber, steel or concrete frames could have been and this school proves it that it is not an inferior substitute. Longs spans have been achieved and a complex design has been easily realised; all done using only timber. One criticism of the structure that could be raised concerns the size and subsequent volume of wooden studs used between the insulation batts. The 280mm thick insulation required 280mm studs to attach to the Brettstapel.
As their inclusion is unavoidable, there is the possible
opportunity to use these studs structurally as they are of a reasonable size to do so. Doing this, however, would almost deem the Brettstapel redundant. The architect is happy with this excessive use of wood and cites the moisture buffering and thermal properties, as well as the aesthetic and health benefits of Brettstapel as primary reasons.
He is also of the
opinion that increasing the use of timber in construction is not only good for the environment but will ultimately help to stimulate the UK timber industry (Foster 07.01.09). This would significantly increase the amount of carbon sequestration within UK forests giving added benefits and helping to achieve carbon reduction targets. 6.35 Summary What the school does prove is that for Brettstapel to be an economic success in the UK, it needs to be manufactured on British shores. The risks were apparent in sourcing Brettstapel from Austria and as a result the project did not have the initial financial benefits expected, nor was it of benefit to UK industries in the short term. If this building were to have been made in the UK using Sitka spruce not only could it have been cheaper, but the return from the timber would have been significantly higher compared to its current market value; this would have been of substantial benefit to the UK timber industry and to the UK economy. Such strategic benefits are not going to be achieved with scattered projects of a similar nature to Acharacle but if this school could be a catalyst for others to follow, then the supporting industries and economy would benefit. Ultimately the school acts as a valuable case study and precedent for those interested in Brettstapel technology.
The decision to use Brettstapel at Acharacle could be said to have been a brave one but it should not be as it is anything but a new technology. It is widely heralded as a successful technology in Europe - it is just the UK industry that needs to be convinced. Will this modest school in Acharacle convince people to take notice of Brettstapel? If the people judging it are concerned more with financial implications rather than environmental benefits then perhaps it will not. The true success of the building however, lies in its construction, in the details, in its huge energy savings, health benefits and ultimately the well-being of it occupants and the overwhelming feeling of being surrounded by solid wood.
Appendix A ECONO Project
ECONO Project In 2004, parties from Iceland, Norway, Sweden, Scotland and Finland set up a collaborative research project called ECONO, focusing on the development of ecological wooden houses. The aim of this project was to develop ecological and comfortable house types that could be turned into a competitive industrial product, and ultimately build physical examples (Arnqvist et al. 2007) Gaia Architects collaborated with North Woods Construction and Brian Burns Associates to develop an ecological structural system suitable for the Scottish environment and based their work around Brettstapel construction. Throughout the course of this project they travelled to Austria and Germany, liaising with manufactures and practicing architects. Their research initially highlighted the benefits Brettstapel construction could bring to Scotland. The large resources of low grade Scottish timber were ideal for use as Brettstapel and the rapid construction time was deemed to be an appealing trait well suited to the wet Scottish climate and poor workforce conditions. The project also noted the high carbon sequestration of Brettstapel was of high value as Scotland became more aware of it position within the global ecological context. The project however also identified potential problems affecting the development of Brettstapel within Scotland. The highly efficient timber frame construction industry was noted as having a 95% share of the Scottish housing market and overall it was deemed to be “exceptionally difficult in the short term for an alternative technology to compete…in this market area” (Planterose 2007). After assessing the potential for massive timber development in Scotland Gaia Architects developed a prototype house with Walter Unterainer, an Austria architect with experience of massive timber, in the hope it would be built in 2006. Unfortunately planning permission could not be attained and the house was never realised. The ECONO project concluded in Scotland in 2006 with seminar and live demonstration of massive timber construction which brought Brettstapel into the public domain. The project partners anticipated a built example would be realised within 2 years of the end of the project in December 2006; Acharacle Primary School will be completed March 2009.
Resources and Further Reading Arnqvist, Liddell, Planterose et al. 2007. ECONO. Eco House North. Oulu: Pohjois-Pohjanmaan Liitto ECONO Project. 2005. Econo. Presentation of the project. [Online] Available URL: http://www.econo.fi/english/project/index.php [Last Accessed January 2009]
Books, Journals and Publications Arnqvist, Liddell, Planterose et al., 2007. ECONO. Eco House North. Oulu: Pohjois-Pohjanmaan Liitto BS 5268-4.1:1990 Structural use of timber. Fire resistance of timber structures. Recommendations for calculating fire resistance of timber members BS 5268-4.2:1990 Structural use of timber. Fire resistance of timber structures. Recommendations for calculating fire resistance of timber stud walls and joisted floor constructions BS 476-20:1987 Fire tests on building materials and structures. Method for determination of the fire resistance of elements of construction (general principles) Bradley, F., 2008. An investigation into the technical viability of a Sitka spruce Brettstapel Timber Panel System. [Technology Strategy Board Grant Application] Davis Langdon Consultancy, 2003. Timber use for construction in the UK. [Online] Available URL: http://www.trada.co.uk/techinfo/library/view/FBE22DA3-E870-45F8-888C8AAB5BD6D884/Timber+use+for+construction+in+the+UK/index.pdf [Last Accessed January 2009] Department for Communities and Local Government, 2007a. Building A Greener Future: Towards Zero Carbon Development. London: Communities and Local Government Publications [Online] Available URL: http://www.communities.gov.uk/documents/planningandbuilding/pdf/153125.pdf
Department for Communities and Local Government, 2007b. Building a Greener Future: policy statement. London: Communities and Local Government Publications [Online] Available URL: http://www.communities.gov.uk/documents/planningandbuilding/pdf/building-greener.pdf
Forestry Commission, 2008. Forestry Statistics 2008. [Online] Available URL: http://www.forestry.gov.uk/forestry/infd-7aql5b [Last Accessed January 2009] Haller, P., 2008. Eminent Structural Engineer: Julius Natterer. Structural Engineering International, Volume 18, Number 2, May 2008, pp. 207-209. [Online] Available URL: http://nattererbcn.com/pics/structural.pdf [Last Accessed November 2008] Halliday. S., 2007. Sustainable Construction. Oxford: Butterworth-Heinemann Joanneum Research, no date, Stone Pine: Positive health effects of Stone Pine. A Joanneum Research Publication [Online] Available URL: http://www.zirbe.info/download/pine_folder.pdf [Last Accessed January 2008] Optiholz. 2007. Optiholz gedĂźbeltes Brettstapelmodul. [Manufactures Technical Information] SchĂśnenberg: Logus Systembau Palmer, S., 2000. Sustainable Homes: Timber Frame Housing. Unknown: Sustainable Homes Publication [Online] Available URL: http://www.sustainablehomes.co.uk/upload/publication/Timber %20Frame%20Housing.pdf [Last Accessed January 2009] Scottish Executive, 2006. The Scottish Forestry Strategy 2006. Edinburgh: Forestry Commission Scotland [Online] Available URL: http://www.forestry.gov.uk/forestry/INFD-6AGGZW [Last accessed January]
Stern, Sir N., 2006. The Economics of Climate Change: The Stern Review. London: HM Treasury Simonson, C., 2003. Past and Future Research on Whole Building Heat, Air and Moisture Transfer. Ph.D. Saskatchewan. University of Saskatchewan Available URL: http://www.kuleuven.ac.be /bwf/projects/annex41/protected/data/UofS%20Nov %202003%20Paper%20A41-T0-C-03-3.pdf [Last Accessed December 2008] Thoma Holz. No Date a. Holz100. [Manufacturers Product & Technical Information] Goldegg: Thoma Holz Research and Development Centre. Available on request from firstname.lastname@example.org Thoma Holz. No Date b. System Thoma Holz. [Marketing Package] Available on request from email@example.com UK Timber Frame Association (UKTFA), 2008. Timber Frame Construction UKTFA Annual Review
2008. London: Emap Inform
Wood. For Good Ltd, 2003. The role of wood in reducing climate change. [Online] Available URL: http://www.trada.co.uk/techinfo/library/view/B335028E-47A8-49BC-A332408E8D0A9FF6/The+role+of+wood+in+reducing+climate+change.++A+summary+of+the+argu ments./index.pdf [Last Accessed January 2009] Personal Communications Bridgestock, M., (John Gilbert Architects), 2008. Discussion on massive timber within the Scottish market. [Conversation] (Personal Communication 11.11.08) Bridgestock, M., (John Gilbert Architects) matt@***.co.uk, 2009. Fire Retardant. . [email] Message to J. Henderson (firstname.lastname@example.org). Sent 07 January 2009, 14:04 Burns, B., (Brian Burns Associates) 2008. Introducing Brettstapel to Scotland. [Conversation] (Personal Communication 07.08.08) Campbell, G., (Dawn Homes) 2009. Discussion on the reception of Brettstapel by volume house builders. [Conversation] (Personal Communication 09.01.09) Foster, S., (Gaia Architects) sam@***.org, 2008. Acharacle Primary School â€“ Heating Calculations. [email] Message to J. Henderson (email@example.com). Sent 5 December 2008, 18:38 Foster, S., (Gaia Architects) sam@***.org, 2008. Acharacle Brettstapel CO2 Calculations. [email] Message to J. Henderson (firstname.lastname@example.org). Sent 16 December 2008, 16:16 Foster, S., (Gaia Architects) 2008,2009. Formal meetings discussing the subject matter of this document. [Conversations] (Personal Communication 9.06.08, 14.07.08, 15.08.08, 08.12.08, 07.01.09)
Gerber, L., (SĂ¤gerei Sidler) email@example.com, 2009. Brettstapel. [email] Message to J. Henderson (firstname.lastname@example.org). Sent 21 January 2009, 15:01 Liddell, H., (Gaia Architects) 2008. Formal meetings discussing the subject matter of this document. [Conversations] (Personal Communication 9.06.08, 14.07.08) Montgomerie. M., (Wood 100) mmontgomerie@***.com. 2009 Price Examples. [email] Message to J. Henderson (email@example.com). Sent 7 December 2008, 10:05 Page 67
Montgomerie. M., (Wood 100) 2009. Conversation on subject of Holz100. [Conversations] (Personal Communication 06.01.09) Wachinger, M., (Holz 100) 2008. Visit to Holz100 Headquarters in Goldegg, Austria. [Conversation] (Personal Communication 09.09.08) Werner, A. et al., (Sägerei Sidler) 2008. Visit to Sidler Sawmill in Oberlunkhofen, Switzerland. [Conversation] (Personal Communication 11.09.08) Referenced Websites DirectGov, 2008. Budget 2008 – protecting the environment. [Online] Available URL: http://www.direct.gov.uk/en/Nl1/Newsroom/Budget2008/DG_073094 [Last Accessed December 2009] E3, 2007. Holz. Haus. Hauptstadt. [Online] Available URL: http://www.e3berlin.de [Last Accessed January 2009] ECONO Project, 2005. Econo. Presentation of the project. [Online] Available URL: http://www.econo.fi/english/project/index.php [Last Accessed January 2009] EMPA, 2008. EMPA in Profile. [Online] Available URL: http://www.empa.ch/plugin/template/empa/2/*/---/l=2 [Last Accessed August 2008] Eurban, 2008. Leno building undergoes a seismic test. [Online] Available URL: http://eurban.co.uk/news_event.php [Last Accessed November 2008] Eurocodes Expert, 2008. Implementation programme. [Online] Available URL: http://www.eurocodes.co.uk/Content.aspx?ContentId=26 [Last Accessed January 2009] Friends of the Earth, 2006. UK motor industry failing to tackle climate change. [Online] Available URL: http://www.foe.co.uk/resource/press_releases/ uk_motor_industry_failing_25042006.html [Last Accessed December 2008] Kaufmann Holzbau, 2008. Dübelholz-Elemente. [Online] Available URL: http://www.kaufmannholzbau.de [Last Accessed January 2009] Longin, no date. Londyb im Vergleich. [Online] Available URL: http://www.longin.at [Last Accessed October 2008] Natural Building Technologies, 2008. Natural Insulations. [Online] Available URL: http://www.natural-building.co.uk/natural_insulations.htm [Last Accessed December 2008] PassivHaus UK, 2008. Basic Principals. [Online] Available URL: http://www.passivhaus.org.uk/index.jsp?id=668 [Last Accessed November 2008] Sägerei Sidler, no date. Optiholz. [Online] Available URL: http://www.sidler-holz.ch/ [Last Accessed January 2009]
Sohm Holzbautechnik, no date. Diagonal D端belholz. [Online] Available URL: http://www.sohm-holzbau.at/start.php?nav_expand=6&action=dd [Last Accessed January 2009] Tschopp, no date. Bresta Massiv. [Online] Available URL: http://www.tschopp-holzbau.ch/w_bresta/site/start.asp [Last Accessed August 2008] Thoma, 2008. Holz100. [Online] Available URL: http://thoma.at/html/english/index1.html [Last Accessed December 2008] University of Southern California, 2006. Simple and High Tech Structures. [Online] Available URL: http://arch.usc.edu/Calendar/Lectures/viewEvent.html?id=856 [Last Accessed November 2008] Waugh Thistleton Architects. Murray Grove [Online] Available URL: http://www.waughthistleton.co.uk/project.php?name=murray&img=1 [Last Accessed January 2009] Wood Awards, The, 2008. The Stadthaus [Online] Available URL: http://www.woodawards.com/the-stadthaus [Last Accessed January 2009] Zirbe, no date. Pinus Cembra. [Online] Available URL: http://www.zirbe.info/index.html [Last Accessed October 2008] Zwick Holzbau, no date. Brettstapel Elements. [Online] Available URL: http://www.zwickholzbau.de [Last Accessed December 2008] Useful Resources Brettstapel www.brettstapel.co.uk www.brettstapel.at www.brettstapel.eu www.holz-suttner.de www.kaufmann-holzbau.de www.longin.at www.merkle-holzbau.de www.natterer-bcn.com www.optiholz.ch www.sidler-holz.ch www.sohm-holzbau.at www.thoma.at www.tschopp-holzbau.ch www.zwick-holzbau.de Government Policies www.direct.gov.uk www.scotland.gov.uk
Massive Timber www.e3berlin.de www.econo.fi www.eurban.co.uk www.finnforrest.co.uk www.gaiagroup.org www.thoma.at www.waughthistleton.co.uk Timber www.alexschreyer.net/projects/timber-dictionary www.forestry.gov.uk www.holz.de www.timber-frame.org www.tonewood.ch www.trada.co.uk www.woodforgood.com www.wood100.com
Other www.eurocodes.co.uk http://www.google.co.uk/language_tools?hl=en http://uk.babelfish.yahoo.com/ Page 69