Spring 21 Building Methods Guide

Guide Selfbuild

THIS ISSUE: BUILDING METHODS

102

CONCRETE BUILDS

108

TIMBER FRAME

115

MODERN STRUCTURAL METHODS

121

OTHER BUILDING METHODS

100 OVERVIEW / 124 THERMAL BRIDGING 128 BUILDING THE DREAM SPR ING 2021 / S EL F BU IL D / 99

BUILDING METHODS GUIDE / OVERVIEW

Spoiled for choice Thanks to advances in technology, there’s more than one way to build a house. This guide shows you what’s on the menu for building your walls.

image: Freepik.com

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Guide Selfbuild

ven though blockwork remains the most popular way to build Irish homes, there are many building routes open to you as a self-builder. Advances in technology have significantly increased the number of methods to choose from, writes Ronan McKee, Director at FmK Architecture.

E

Ronan McKee, FmK Architecture Ltd & FmK ECOHomes, fmkni.com

Choosing your building method is one of the most important decisions you will make, and it is one to make at the very start of the design process. This is because how you will actually build your house will have a knock-on effect on the design, and vice versa.

For example, some products like ICF blocks and other manufactured materials will come in predetermined dimensions (length x height) and to save on costs, the wall or opening sizes, or floor to ceiling heights may be designed to work around these standard sizes so as to minimise cutting, waste and labour time on site.

It holds true that the more bespoke and complicated the shape, the more expensive it will be to build, but other design considerations such as solar orientation, layout for space and light, as well as aesthetics will also help guide your choice of build route. In addition to this if you are aiming for a low energy or passive house, you will need to choose compatible methods, materials/ products and techniques in order to reach your goal.

In other words, depending on your design, some structural or design constraints may make one method of building more expensive or cumbersome than another.

For instance, curved walls are tricky to build with blockwork or timber, but relatively straightforward with Insulating Concrete Formwork (ICF).

Cost is indeed a major factor but with stricter requirements in terms of energy efficiency, especially in

ROI, the difference between building with blockwork versus other methods is rapidly shrinking.

On the topic of energy efficiency, timber frame traditionally had the upper hand when it came to ensuring an airtight and well insulated build, as installation is the key to achieving a high level of energy efficiency, and blockwork can be more prone to human error than wall sections built off site. However, the gap in this is massively reducing due to greater thought process and detailing of junctions and thermal analysis by specialist practices and designers.

Indeed, all building methods can adapt to your plans and specifications. No one method is inherently better than the other.

It’s all about making sure the building method fits the design and whether you are deciding on a main contractor or direct labour (hiring the trades yourself) route. In addition to this it is paramount that you have all of the details worked out before you get to site.

Other factors that could influence your decision are the availability and expertise of tradesmen. For instance, block layers may be in plentiful supply, but if you are asking them to do the insulation and/or airtightness make sure they are trained to do so.

You may also make a decision based on the building materials’ credentials, including factors such as embodied energy to reduce your carbon footprint, vapour permeability and low VOC content for good indoor air quality, thermal mass for energy efficiency or simply

wanting to build with a natural, renewable material.

Whichever build route you choose, make sure you have robust construction drawings, based on a well thought out insulation, airtightness, ventilation and thermal detailing strategy devised by an architect or designer who is qualified or well trained in low energy or passive house design.

A good indicator of this is a

construction drawings) to check progress or any issues, as well as do quality control checks, will be invaluable. That’s because the devil really is in the detail when you are on site.

On that topic, a word of warning.

Don’t fall into the trap of listening to tradesmen who will try to persuade you to downgrade the construction drawings/details to a more basic

Certified Passive House Designer or Consultant.

This is then well aided by finding the right contractor or tradesmen to build it for you; there is no point bringing in a low energy minded joiner or plumber/electrician at the end of the project. Correct installation and attention to detail must be got right from the start.

Having a qualified building professional (often the same person who put together the

design. Their input may of course prove useful, but never change the construction drawings without consulting with your designer.

As with all aspects of selfbuilding, do your research and thoroughly double check references, getting at least three prices for everything. Once the design and details are set out and agreed, the contracts all signed, it should be plain sailing from there. In theory at least!

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BUILDING METHODS GUIDE / CONCRETE BUILDS

Concrete builds Building your walls out of concrete will usually take the form of the ever popular block build, but there are other options to consider.

What ise? concret

ent, ade up of cem Concrete is m ixture of m a n te of , egates water and aggr materials that enhance and crushed rock entials. Not to d/or eco cred an al its therm ch is cement hi ith mortar, w w ed te us nf co be sand. Concre ater, lime and for er ix m t mixed with w en m on site in a ce can be mixed ght on site in it can be brou s, he tc or can small ba ur to be po ed, ast a cement truck ec pr te si g in ild come to the bu c shape. in a specifi

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Concrete as a building material is often part and parcel of a selfbuild. In the majority of cases, it is the primary material you will use for your foundations. Your floors and screeds, window sills and lintels, and even perhaps your roof covering, might also be made of concrete.

Because masonry is so commonly used in Irish domestic building, almost every building contractor has tradesmen at his disposal who can do a professional job. Many masonry materials are manufactured locally and are readily available from local builders’ merchants. Meanwhile lenders, insurers and warranty providers are comfortable with extending credit or cover for concrete builds.

Concrete is a strong material that boasts excellent fire and acoustic properties. It’s long

lasting as it is not subject to rot, decay, moisture or UV damage, corrosion, or infestation, and it can be reused once crushed.

The trade off is that concrete is heavy and requires more foundations (i.e. more concrete) to support its weight. Concrete also doesn’t tolerate movement, an issue where the ground conditions are poor and a good foundation hard to achieve.

Especially relevant to low energy buildings, concrete and masonry in general absorb heat in hot conditions then release it back into the living space, acting like a whole-house storage radiator.

This is often a key design feature of a near zero energy house. And because masonry relies on using small units of construction, you have design flexibility.

However, concrete has a high embodied energy. In other words,

Guide Selfbuild

it takes a large amount of energy to produce cement. Manufacturers are addressing this challenge by increasing their use of renewable fuels, with the European cement industry aiming for carbon neutrality by 2050, and replacing cement in concrete mixes with waste byproducts.

Quarrying also has an environmental impact from the point of view of water use, an issue for slate manufacturers too, but the industry has been investing in sustainable extraction methods to mitigate the impact.

Cavity wall construction (blockwork)

The most traditional masonry build technique in Ireland continues to be what’s called a block build, or cavity wall construction.

It consists of two rows of blocks or bricks; the inner leaf is often built from regular or lightweight concrete blocks and will usually be built before the outer leaf, although they can be brought up at the same time.

Wall ties, added at regular intervals sloping downwards towards the

outer leaf, join the two leaves. The blocks are cemented together with mortar.

The inner leaf is the structural component, and thanks to the compressive strength of the concrete blocks, the wall itself becomes the main support for your building.

The cavity between the two layers was originally used to act as a buffer from the elements (to reduce the risk of moisture soaking through) but it is now also used to add insulation, either fully or partially.

Insulating the cavity is specialist work in that the insulation needs to be fully joined at all points and there can be no snots or mortar droppings in the cavity; either of these two scenarios would lead to thermal bridging (see p124). If the insulation is not tight against the internal leaf, a phenomenon known as thermal looping will also greatly reduce the insulating effect.

It’s customary to create weep holes at the base of the outer skin to allow water that might penetrate this veneer to escape outside rather than collect in the cavity between.

Cavity trays, with associated stop

Waste materials as cement substitutes The most common substitute for cement in the making of concrete in Ireland is a by product of iron manufacturing called GGBS, an acronym for Ground Granulated Blast Furnace Slag. A replacement rate of up to 70 per cent (so 30 per cent Portland cement in the cement mix that goes on to make concrete) is possible under I.S EN 206-1.

An Australian company, meanwhile, is substituting sawdust and other recycled timber, e.g. from discarded pallets, to its mix of cement to make eco-friendly concrete bricks and panels, among other products.

Mostly still at the development stage is Ferrock, which uses steel dust and fly ash to make a cement alternative, capturing CO2 during the curing process. The availability of the waste materials is a barrier to further development. The patent is held by the University of Arizona.

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BUILDING METHODS GUIDE / CONCRETE BUILDS

ends and weep holes, must be used above structural openings and above all external wall penetrations.

Though concrete blocks are a relatively recent development from the 1920s, it is only since the 1950s that they completely replaced bricks as the inner leaf of the cavity walling. Bricks are more expensive, and therefore not as readily used because many self-builders nowadays plaster or clad (with stone, for example) their external walls anyway.

The size of the cavity within the blocks has increased over the years to add more insulation; nowadays 150mm cavities are commonplace if you insulate with EPS beads but this can be reduced if you used high spec boards.

The size of the cavity will depend on the type of insulation you choose (how good its thermal properties are), whether you full fill or not, and what overall U-value or thermal performance you want to achieve (there is a minimum specified in the building regulations).

Insulation methods

The two most common and cost effective ways to insulate your block build is to either pump the cavity with EPS beads, or install PIR or phenolic rigid boards as the wall is built up. You can also use closed cell spray foam insulation to full fill the cavity, but it’s a more expensive option than the other cavity filling methods.

Insulating externally is also more expensive and therefore not common on new builds, unless it is an intrinsic part of the building method (see Single skin construction below). However for existing buildings it has become a go-to for solid masonry, and some older cavity wall types of construction.

Whether or not you also insulate the internal wall, the one facing inside the house, usually with insulated plasterboard, will depend on your insulation strategy.

Structural concrete blocks are 10 4 / SE LF B U ILD / S P R I NG 2021

therefore usually surfaced with plaster, sand and cement mortar, or covered with (often insulated) plasterboard to produce the internal wall finish Graphite EPS beads required and add a layer of airtightness.

Synthetic fibres incorporated into the sand and cement finish can increase the strength of a block wall considerably.

Your energy assessor will evaluate your options; this is specialist work that takes into account your insulation strategy as a whole – for the entire dwelling, so that there are no weak links.

Types of blocks

There are three main types of concrete blocks. High density ones made from cement and an aggregate; lower density ones made using cement and industrial

Board insulation in cavity wall

Guide Selfbuild

but it is, of course, still a wet trade involving the use of small construction units, just like any other masonry system.

Cast concrete

wastes/fly ash as the aggregate; and lightweight blocks (including autoclaved aerated blocks) that are easy to lift and use, simple to cut, have good thermal properties and can be made of up to 80 per cent recycled materials.

The standard size of a block is 440mm x 215mm x 100mm but larger sizes are also available, both solid and hollow. It takes ten standard sized concrete blocks to build one square metre of wall.

Blocks are usually laid vertically (standing on their long thin edge) but can be laid on flat. This latter method makes for a very strong, solid concrete wall in situations where it’s not possible to cast one from poured concrete.

The advantage of concrete blocks is that, being larger they go up faster than bricks. Some blocks, especially concrete types, also absorb less water than brickwork.

Concrete blocks that have a hollow centre can be reinforced with steel and sections filled with concrete where required, to make the structure very strong. A variant of the concrete block that is gaining popularity is the clay block which is more thermally efficient.

This has hollow cavities within it to improve its insulating properties and can be used to build a single skin wall in certain circumstances.

Once on site, blocks have to be carefully stored, out of the wet,

on site ready for use; a chipped brick or fractured block is no use to anyone. Weather is another consideration and new work will have to be protected from frost and heavy rain.

Single skin construction

Single skin construction includes prefabricated concrete external wall units, which used to be the sole remit of commercial buildings.

Precast units are quick and easy to install and are brought to site as needed so there’s no problem with storage. They provide a very good thermal mass but they are also on the more expensive end of the scale and are still rare on selfbuilds. Non load bearing concrete precast wall units can be used for up to eight storeys or fixed to a steel frame.

An Irish single skin construction system uses 200mm wide blocks that are quickly installed using thin bed mortar, then finished externally with EPS insulation, followed by several other layers to complete the watertight and airtight system.

The inside of these lightweight blocks is completed with dot-anddab plasterboard. It is claimed that this system can cost up to 20 per cent less than timber frame

Concrete can also be poured on site to create walls, a prominent example being ICF (see next page).

Another reason to pour your walls is if you want a specific kind of architectural detail, e.g. by using sandblasted wood boards as your formwork to make an imprint on the concrete. This can be done internally and/or externally.

Of course foundations and floors are also cast in situ, from the subfloor which is made of concrete along with the screed, although the latter can be made of a cement mixture. The mix for a polished concrete floor will have been determined in advance with your supplier. These processes require hiring a cement truck to do the pour on site.

What about flooring?

The most common option

nowadays for upper storeys is to use concrete hollow core or wide slabs, craned into place on site. A concrete upper floor is considered more suited to underfloor heating, as a screed covers the piping, which may mean that you will need to use radiators if your upper floor is solely made of timber although nowadays timber solutions are also robust. Remember that a concrete floor will be heavy and will require adequate support from the foundations, i.e. more concrete.

Another option, especially in the case where accessibility is an issue, is the concrete beam and block method whereby concrete blocks are supported on reinforced concrete beams. The joints are grouted and a screed is then applied on top. The strength of the beam and block method allows wider spans of flooring to be constructed without needing extra support.

It is important to research this area prior to construction and select the type of flooring that is most suited to your needs and to select a supplier to consult them on your design. They will be able to

Information compiled from articles by Andrew Stanway.

Additional information: cembureau.eu

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The Greenest energy Is the energy We Don’t use The built environment is a significant consumer of energy and therefore must be a focus for energy saving efforts.

Renewable energy technologies cannot work alone to conserve our energy consumption and must not be inefficiently implemented to bridge the gap of our building’s performance. Therefore, we cannot consider them as a substitute for enabling more efficient building performance.

Low energy buildings concentrate on minimising heat loss rather than increasing consumption to bridge the performance gap.

Renewable energy technologies and low energy buildings share the same desired environmental outcome however the systematic approach is wrong. Our efforts should be on improving our buildings performance with the intention to fully utilise the potential of renewable energy technologies thereafter.

It is our responsibility as contributors of the built environment to resolve a more sustainable and socially responsible way of building.

We are taking pride in our buildings, our intentions and our impact.

pbsltd.uk e. info@pbsltd.uk | t. 0330 133 2511

PASSIVE BUILDING STRUCTURES 10 6 / SE LF B U ILD / S P R I NG 2021

Guide Selfbuild

advise which method is most cost effective for your requirements, e.g. to support upper floors, requirement for open spans, etc.

The supplier will normally turn around an order very quickly once as-built measurements can be taken on site. Builders may also wish to incorporate balconies and stairs when ordering precast units which will also be manufactured to exact dimensions.

Insulating Concrete Formwork

Insulating Concrete Formwork (ICF) is a wall building method that consists of large, hollow, lightweight polystyrene blocks that lock together to create a mould that is then filled with concrete to make structural walls. It can be used to make roofs too.

The ICF blocks fit snugly together vertically and horizontally and the two leaves are kept in position by various patented metal, plastic or polystyrene spacers.

Blocks can be cut on site with a hot wire or a handsaw, but this will be done sparingly as the house will have been designed around the block measurements to minimise waste (in time and materials).

Specialised components such as lintels can be ordered with the package. Many companies have flooring systems that allow you to cast both walls and middle floors at the same time.

ICF has all of the benefits of concrete builds, and in addition is intrinsically airtight and virtually thermal bridge-free – a big advantage over other construction methods. U-values can be as good as 0.11W/sqmK but you will have to pay extra to add layers of insulation.

It’s quick to erect, can involve DIY help with oversight, is not overly susceptible to bad weather and offers flexible designs in that curved walls are relatively easy to achieve. As soon as it’s complete, it’s watertight and once it’s roofed, follow-on trades can get cracking much earlier than with other building systems. Manufacturers claim that self-builders can save up to three months on their schedule using this method.

There are several different ICF systems, some of which can cope very well with concrete middle floors, internal walls and all kinds of design requirements. But making changes later (for example adding or moving doors, windows or services) can be difficult and expensive as compared to blockwork construction which is easy to alter. You’ll find yourself having to rely on ICF experts with specialist cutting tools and they don’t do this work cheaply.

Without a doubt, the most skilful part of ICF is the pour. Most companies will advise you on this well before you start your project and at your training days you’ll learn how to support the walls so they don’t sag or, even worse, burst as you load them with tonnes of

wet concrete.

You’ll be told how high you can build any given wall before it needs filling. Different companies have their own recommendations on this and you’ll need to hire a concrete pump, and your site will need to be accessible.

The concrete itself also has to be at exactly the right consistency (wetness) or it won’t flow into all the cavities of the formwork.

Some companies insist that you use a particular grade of concrete (aggregate size). Finally, if you are going multi-storey bear in mind that multiple visits of the delivery trucks will cost you.

In terms of finishes, the outer skin of the polystyrene blocks has to be clad (using built-in fixings or wall ties) with something – it can’t be left open to the elements. This outer skin can, though, be easily chased to make room for rainwater downpipes and even other utilities.

In many cases you will need proprietary fixings to finish the external and internal walls, and you can achieve whatever external appearance you want. You could, at this stage, add even more insulation, depending on the U-values you’re aiming to achieve, before your final cladding.

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BUILDING METHODS GUIDE / TIMBER FRAME

Timber frame

Timber is naturally breathable and eco friendly; we look at how homes are built with this material in Ireland.

Words: Julian Owen, author of Kit and Modern Timber Frame Homes, ISBN 9781 86126 9508, Crowood Press

“

Most of the countries in continental Europe are ahead of Ireland in terms of the use and diversity of timber frame houses...

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There are many ways of forming a frame with timber. The type that is built from scratch, on site, using wood from a builder’s merchant, is rare in Ireland but relatively common in the USA. A mixture of bureaucracy, the current lack of sufficiently well-trained carpenters and unfamiliarity with the techniques involved amongst other building trades make this more difficult here.

In fact in the USA and Canada, there is a long tradition of building in timber frame from abundant locally available raw material.

There are even a number of North American manufacturers who fabricate timber frames (post and beam construction, often using long length of timber) including windows, doors and cladding and export them as a kit for assembly in Europe as a watertight shell.

Cedar cladding is often used, as

well as structural softwood such as spruce or fir, with glazing often up to ridge height. These houses have a distinctive open plan style that shows off the high quality native timber to good effect.

Most of the countries in continental Europe are also ahead of Ireland in terms of the use and diversity of timber frame houses and in general terms are also more adventurous with design and technology. In a modernist tradition, German manufacturers often place a high priority on expressing the construction of a house in the design and making it an integral feature of the appearance. German post and beam construction tends to be prefabricated and exported to the UK to a very high standard of design and construction, making them relatively expensive.

But for the purpose of this

Guide Selfbuild

Open vs closed panel Open panel timber frames

There are two main approaches to assembling the structure of a timber frame building, and most systems that use studs, joists and rafters are a variation of one of these:

The platform frame method of assembly is generally used for the open panel system, because the short sections of timber needed lend themselves to prefabrication and transport to site – longer Platform Frame timber would require a special With this method, the ground floor lorry. walls and first floor structure is Internal walls that are not erected and the resulting platform carrying any load are usually is used as a base upon which supplied along with the rest of the to construct the next floor. This Fibre cement example by Cedral Thrutone Endurance frame, but can be improvised on means that the whole frame can site if necessary. If the internal be built on site from relatively wall is part of the structural short timber lengths. design of the frame, it must be manufactured as part of the kit.

Balloon Frame The panels support the roof The balloon frame method and are in an identical location is similar in principle to the within the structure to that of the platform, but the walls are built block work inner leaf of a masonry as a continuous structure, from cavity wall construction. The voids ground floor level up to the between the studs are filled with eaves. A benefit is that once insulation. made, the frame can be erected Because warm air from the to a watertight stage faster. The house carries moisture, the balloon frame cannot usually go internal lining of an outside wall higher than two storeys because usually has a vapour control there is no timber sufficiently long layer, such as a foil backing to the enough to reach further in one go. plasterboard, to stop air leaking into the inside of the panel. To disperse any vapour that does find its way in, the outer sheathing of

n Features of a

Dermot Byrne Photography, dermotbyrne.ie

article, we look at the Irish timber frame systems most commonly available on the market. These are kits that depend on factory prefabrication. This means the frames are certified and pre assembled to be as cost effective as possible.

It also means these structures are built to be fire resistant, rot and pest resistant and are very good at keeping noise out of the building.

Timber is a natural material that is vapour permeable, which when sustainably sourced, provides the benefit of being renewable.

The insulation, airtightness and ventilation strategy is essential to get right, as timber can decay, and you will have to follow through with the design you agree to as alterations on site will prove difficult.

The most widely available type of kit is the open panel. It is popular because it is easy to put together both when the prefabricated parts are made and when it is assembled on site. In the factory, softwood studs form the main structure, and a rigid board such as plywood provides bracing.

These are simply nailed together to form a strong, rigid panel, designed for easy delivery and assembly. The studs and the panels fixed to them are both crucial elements of the structure and if either is damaged or missing, the strength of the panel is reduced. The name ‘open panel’ derives from the fact that when the panels arrive on the site one side is open and un-boarded.

It is usually left open until the building is weathertight at which point services and insulation are put into position. It is closed over with a sheet of plasterboard or a gypsum-fibre board along with a vapour control layer to prevent condensation within the panel.

Assembly

OPEN Panel e Timber Fram

ion on site Fast construct material y an in Can be clad d rt – robust an po ns tra to Easy d ire pa re ly si ea damage erials use of the mat Cost effective ilders bu nds on selfSuitable for ha ible ss po n tio sula High level of in on tions Limited altera le site are possib Cedar shingle roof covering Paul Lindsay photography

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BUILDING METHODS GUIDE / TIMBER FRAME Features of a

el CLOSED Pan e Timber Framction

the external wall is covered with a breather membrane, that keeps out water (such as rain) but also allows vapour-laden air to pass through to the outside of the frame.

The timber structure of an open frame is never exposed and would not look very attractive even if this were possible. The outside cladding can be almost any building material, including bricks, softwood boarding, tiles and render. When brick cladding is used, only an expert eye will be able to spot that there is a timber frame concealed behind it.

ity of constru Very high qual in the factory ing assembled Most of build tion on site.

Very quick erec port g during trans Careful handlin after te si k needed on .

Very little wor ab sl or flo d an groundworks d on site ire qu re ur bo Low level of la n r improvisatio Little room fo on site

Closed Panel Timber Frames

If the framework of studs is enclosed on both sides it is called a closed panel system. The panels are factory-made in their entirety, including the insulation, electrical wiring and window and door linings. The main job required on site is to assemble them, after which the inside is ready for fitting out and decoration.

The idea is that once it is in

place, the wall will not have to be drilled or cut. If this happens, the panel is damaged and careful repair is needed. As a result a very high degree of pre-planning is necessary. The position of anything that is to be fixed onto the walls, or supported by them

in any way has to be built in when the panel is made.

Assembly once the panels have been delivered to site is quick, although relatively large lorries will be needed for transportation with cranes to lift the panels. Apart from the speed of erection and

higher quality control, another benefit is that the building is easy to make air tight. Once in position, the frame is then clad in whatever material is required, in a similar way to the open panel frame.

Green Oak Frame

OAK Frame n Constructio

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a cladding such as tiles, timber boards, render or brick.

Often referred to as ‘green’ oak, because when relatively freshly cut it is fairly easy to saw and shape. Once felled, the timber gradually begins to harden and become impervious to water. After about 18 months to two years, it has become so hard it is resistant to insects and difficult to cut or sink a nail into. As the green oak matures, it dries out and begins to shrink, twist slightly and even develops small splits. In an ordinary building this may be considered a disadvantage and no one should choose a green oak house unless they accept that this is part of the character of the material and key to its charm.

Andrew O’Brien Architects

There is a very strong element of nostalgia that attaches to traditional timber buildings and those genuine examples that have survived are greatly prized. However, there are many companies that have studied traditional methods of construction and do their best to replicate them.

One advantage the new buildings have over the real thing is that they comply with modern standards. A much higher level of insulation is possible and they also allow modern layouts and room sizes.

These buildings are not the cheapest in n Features of a comparison to the other types of frame and require a relatively generous budget.

The modern oak framed house takes the practices and principles of carpenters pearance ap l from the middle ages and re-interprets na tio di Authentic tra nstruction them using twenty first century factory co ity al qu h Hig as part d se prefabrication methods. Chunky es pr ex Structure is beams, columns and rafters are of the design s for finishe assembled with slotted and dowelled rally – no need tive Weathers natu va er es pr joints just like the traditional frames.

- no Very durable s se ca t os The building is clad either by filling the m in needed gaps between the posts with insulated n plan’ design pe ‘o to d ite Su panels, or covering the whole structure with

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Log construction Colloquially known as ‘log cabins’ this system has its origins in what was probably the earliest form of timber construction. Most kits originate mainly from Scandinavia, particularly Norway and occasionally North America.

The basic concept of logs piled up on top of each other to form walls with dovetailed joints chopped out at the corners to interlock has been developed into a more sophisticated version. Chunky sections of timber are shaped by machine so that tongue and groove joints along their length interlock as they are stacked up to form the inner leaf of the wall.

The logs can be flat, oval or round to imitate true logs. Timber alone is usually not a good enough insulator to satisfy current regulations, so there is then a layer of insulation, usually faced with timber boards on the outside. Alternatively, the structural wall can be insulated internally and dry lined. Either way, log construction is more energy efficient than ordinary timber frame, because the bulky timbers absorb and store more heat than the relatively lightweight timber studs and posts.

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Boyd Cody Architects

Weighing the options

Kieran McCarthy KMC Homes

Kieran McCarthy ponders the benefits and setbacks of the most common building methods in use in Ireland today: blockwork, timber frame and ICF. For you to make an informed building frame decision, you need to evaluate your project in terms of budget, complexity, structure and program. Keep in mind, of course, that whichever method you choose to build your home, it will be designed, as a prerequisite, to be building regulations compliant for strength, durability, airtightness, insulation and so on.

Very broadly, blockwork is the most cost effective but complex and tedious to execute in that there is a myriad of moving parts to watch, including setting-out and detailing, as well as cold bridging and the material’s sensitivity to wet, windy or subzero weather. You also have to manage the delivery from a large heavy truck

and lifting onto loading bays for the masons, with scaffolding needing adjustment, all of which comes with complex health and safety obligations.

Timber frame costs a little more but is a considerably quicker method and will offer many benefits as many of the headaches are dealt with by the timber frame company. But as the house is factory built, there is no room for measurement error (key decisions must be made early, e.g. exact window sizes, kitchen layout) and considerable care on site must be given to the correct ventilation and insulation techniques which are unique to timber.

Key areas to watch here are setting out of the blockwork base so the panels can slot in, the fact that the sections will arrive flat-pack on an articulated

There are of course variants on each of these themes and other alternatives, and it is an area you will need to thoroughly research early on in the process. kmchomes.ie

truck, and that they normally are erected on site using a mobile crane (heavy winds will affect crainage) supplied and operated by the timber frame company.

ICF will also likely cost more and is a little more like blockwork in terms of the daily setting-out requirement, but the insulation forms are lightweight and relatively simple to install, making it suitable for hard to reach sites. ICF can also easily be adapted for use as retaining walls. Fixing steel is a little more tedious and the concrete is poured using a concrete pump which needs site access; there is also a significant bracing process required to ensure no movement of the form structure when the concrete is being poured, a task best left to the experts.

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BUILDING METHODS GUIDE / TIMBER FRAME

Kit suppliers The content of a kit varies significantly between different suppliers. Some provide the frame for the walls, floors and roof and no more. Others offer everything that is part of the construction that is made of timber, including windows, doors, staircases and skirting boards. These extra items included in a kit package should be carefully scrutinised. Sometimes, in exchange for the convenience of not having to choose or source the items, there may be a significant mark up compared to the cost of supply by a builder’s merchant.

Some firms do not actually make the timber frame themselves.

They ‘add value’ to the basic product, which consists of timber and boarding, by offering design and management services or the convenience and relative predictability of building a predesigned house that has been refined and perfected over the many times that it has been made and built.

On first enquiry most kit suppliers will confirm that they will readily customise their designs to suit a client’s requirements.

However for some of them, this may mean that

they will move a few internal walls around but be reluctant to make any significant changes in the overall dimensions or appearance.

Others, particularly at the higher end of the market, will happily design a unique house for an individual family.

Programming the project

The majority of the work constructing a timber frame is by specialist tradesmen with much of it being carried out in factory controlled conditions. In some cases such as with a green oak frame, the entire structure will e ill often us have been already kit suppliers w e e m us fra so r al be ay m Ti aterials but m m n assembled in ic tio ol la en su ph in as PIR or breathable aterials such the factory as a ts m n uc tio od la pr su n in tio modern many insula ct fa ‘dummy run’ to in ur e yo ar e of boards. Ther ill form part eliminate any n in all of which w io , at m er fro id se ns oo co to ch eds careful ne ch problems that may hi w d . an strategy specification ur airtightness otherwise occur l or ra tu na e us tandem with yo that mostly es e ur th unexpectedly on ct ru as e st m or e timber fra Eco builds, e site. Erection of a , will often us ar ls ia at er th s at m ild le bu renewab or hemp ructure. Straw s to work kit for a small very supporting st ber as the basi tim e us lly straightforward ca pi t). ty ki ill a w ot en (n DIY driv built on site e m house may only fra a l e fil from to clay or lim asters such as take three days, a l ra Breathable pl ed with natu larger frame may take have to be us products. n tio la su in

Eco builds

1 1 2 / SE L F B U IL D / S P R I N G 2021

a couple of weeks. Generally a house built with a timber kit will be finished more quickly on site than an equivalent sized traditionally built masonry cavity wall structure, although there is usually a long lead-in time between ordering the kit and delivery onto site, typically three months or more.

The crucial point in the programme is the arrival on site and erection of the kit. The necessary preliminary works must have been completed and the base must meet the tolerances and standard of construction specified by the suppliers – level, square and of the correct dimensions.

This is crucial. If the base is not ready the erecting crew will return to the factory and extra costs will be incurred to cover the abortive visit and for the storage of the components.

Site set up materials and delivery

Once a delivery date has been agreed with the frame supplier, the onus is on the main contractor and client to get the substructure ready on site to receive the frame.

For a larger project or if there is very limited space on the site for

Guide Selfbuild

storage, delivery may be in two or three stages, but usually most of the kit will arrive on one day, with some other items such as roof trusses or chipboard following later. It is possible that some of the peripheral items bought from the kit supplier, such as plasterboard or insulation will come directly from the manufacturer and it may be necessary to arrange delivery separately with these companies. Everyone on the main contractor team must be aware of all the delivery dates and their importance, so that the necessary

work is complete and ready when the erectors arrive on site.

Always check early on that vehicle access to the site is adequate for the delivery lorries.

To be ready for the frame to be delivered and erected: l Date, timing and content of deliveries agreed and confirmed in writing. l Substructure, walls and ground floor (if concrete) ready and built within the tolerances specified by the kit supplier. l Space within the site for temporary storage of the larger components. l Tarpaulins available to protect loose timber items. l Secure, dry storage, available e.g. portacabin or container l Locations of any cranes on the site worked out and agreed. l A clear, unobstructed route wide enough for the delivery lorry prepared. l Someone to be present on site responsible for co-ordinating with the kit supplier. l A full set of drawings, specifications and fixing schedules available on site. l Scaffolding must be ordered and coordinated with the kit supplier’s build programme.

and has the agreement of the supplier, a specialist team from the supplier should be used to erect the frame. The skills required are over and above those of a typical carpenter on a building site, because the frame has been made to very fine tolerances and each system has its own idiosyncrasies that must be respected. If the frame is erected by the supplier, it also provides a single point of responsibility should any problems develop.

Accurate setting out of the position where the foundations are to be placed is essential as the kits are precision made with tight tolerances. ‘Setting out’, that is creating a precise template for the general builders to work to, usually indicated by pegs in the ground

with string run between them, is a crucial job. The joints need to be very tight and secure for their structural integrity – the result is a very rigid box, to an exact size.

The slab must be very level and absolutely square in plan, if not, the frame will settle once it is in place and not fit together properly.

Sometimes the plasterboard lining is designed as part of the bracing or racking to the walls, and if this is the case, the temporary support should remain in place until the lining of the internal face of the walls is complete. After the frame has been erected, the scaffolding has to be moved out slightly all around the outside of the house to allow space to either fix cladding or construct a skin of masonry. The breather membrane

Erection of the frame

Unless the general builder has extensive experience with the particular kit system being used

Kilbroney Timberframe, Valley Business Park, 48 Newtown Road, Rostrevor, Co. Down, N. Ireland. BT34 3BZ T: (028) 4173 9077 E: info@kilbroneytimberframe.com W: www.kilbroneytimberframe.com

SPRING 2021 / S EL F BU IL D / 113

BUILDING METHODS GUIDE / TIMBER FRAME

and roofing felt are fitted as soon as possible after the frame is up to help the frame to start drying out and provide a sheltered interior for other trades to start work inside.

Completion of the general builder’s work

Once the frame is in place and the erection team have left the site the general building tradesmen move in to complete the house. There is less room for the builder to improvise when working on a timber frame.

Moving an internal wall or drilling a large hole in a floor joist for a drainpipe are to be avoided, and all the manufacturer’s specifications with respect to fixings such as ties and straps should be followed exactly. Any departures from the specification and drawings for the kit must be approved by the supplier or a structural engineer.

Who Does What on Site (Typically) Main Contractor Design Build

Main Contractor Build Only

Direct labour (Managed Sub Contractors)

DIY Build

Site Preparation

Main Contractor

Main Contractor

Groundworks Contractor

You

Foundations

Main Contractor

Main Contractor

Groundworks Contractor

You

Drainage

Main Contractor

Main Contractor

Groundworks Contractor

You

Erection Kit Frame

Kit Supplier, usually paid

Kit Supplier usually

Kit Supplier

Kit Supplier

by Main Contractor

paid directly by Client

Main Contractor

Main Contractor

General building contractor or

You

Cladding of Kit Frame

specialist such as bricklayer You

External Windows and

Main Contractor

Main Contractor

General building contractor

Doors

or part of kit

or part of kit

or Joiner or part of kit

Internal floors

Main Contractor

Main Contractor or

General building contractor

part of kit

or Joiner or part of kit

Main Contractor

Main Contractor

Joiner

You

Main Contractor

Main Contractor

Plumber and Electrical

You, but regulations require

Contractors

some aspects by approved

Internal fixtures e.g.

You or part of kit

doors Plumbing and Electrical Work

contractors Decorations

Main Contractor

Main Contractor

Decorating Contractors

You

Landscaping

Main Contractor

Main Contractor

Landscape Contractors

You

11 4 / SE LF B U ILD / S P R I NG 2021

BUILDING METHODS GUIDE / MODERN METHODS

Modern structural methods With technology moving so fast, it’s no wonder there are plenty more options open to self-builders to build their home.

Most modern structural methods will involve a higher upfront cost to build the walls but will usually save on both labour and time on site. The energy efficiency of the building will also help to balance the cost comparison – with modern methods you usually get the guarantee of an airtight and well insulated home as part of the package.

Structural Insulated Panels (SIPs) This method of construction, which is timber panel rather than timber frame, has long been used in North America, but it is a comparatively recent innovation in Europe. Instead of using timber to form a frame, SIPs consist of timber-based boarding, sandwiching sheets of rigid foam insulation such as expanded polystyrene.

The two materials are firmly bonded together so that they effectively act as a single structural component. The resulting panels are said to be five to ten times stronger than conventional timber frame. In Europe, they are used mainly for internal and external walls, although they are increasingly replacing rafters because they provide a clear roof space that can be used for bedrooms. The first SIP houses in Europe were built from panels shipped from America, but there are now factories in the UK, Ireland and the rest of Europe.

The insulation is more effective in comparison with other systems and masonry construction. In addition to this, the walls to SIP houses are relatively thin, freeing up more space for use in the rooms of the house – a factor that could be important on a cramped site. The relatively airtight construction is a major contribution to energy efficiency by reducing the amount of warm air escaping in winter.

On site a crane is needed to manoeuvre the panels into place and assembly on site is a job that is best left to specialists, who slot them together and seal the joints.

The structure of an average sized house (e.g.150 sqm) can be assembled in two or three days.

Cost wise if you choose a standard design, it should compare well to other methods that achieve good airtightness and insulation standards.

However more common are bespoke designs which will inevitably come at a higher cost.

WINT SPRIN ER G 2021 2020 / S EL F BU IL D / 115 121

BUILDING METHODS GUIDE / MODERN METHODS

“

Cross laminated timber (CLT) is another innovation that’s come of out of timber R&D departments

Cross Laminated Timber house by architect Micah Jones.

Mass timber

Timber as a material is structural, vapour permeable and renewable when sustainably sourced. To make it even stronger, engineers have developed a steel alternative that is known as glulam, which can replace steel supports (RSJs and the like) in domestic builds.

This structural material is not only used as support beams, it can also become a whole house construction method (see page 128).

Cross laminated timber (CLT) is another innovation that’s come of out of timber R&D departments, consisting of planks of timber glued together and layered at right angles to produce a sandwich made up of three, five or seven layers which form solid timber panels 3.5m wide by up to 22m long. These huge sheets of CLT are then fed into an enormous CNC (computer numerical control) machine which uses precision engineering to cut the panels needed for your project.

Doors and windows are simply cut out like cookie dough and even drilling out ducts for plumbing and wiring can be done in the 11 6 / S E L F B U IL D / S P R I N G 2021

factory before the panels are finally stacked on the back of a lorry in the correct order for assembly on site. The structure is then usually externally insulated and clad.

Professional input at both the design and construction stages is essential for either of the methods, so as to produce a design that plays to the strengths

the material has to offer. CLT can create intricate roof forms, simple cantilevers and even lightweight structures placed on top of existing buildings.

In the case of CLT the erection of the panels is also a specialised process; they can weigh several tons and fixings must be accurate and correct for the structure to

work. The builder then completes the insulation, roof and cladding as well as all the internal work.

The waste, which is cut from the windows and doors in the factory, can be delivered to site along with the rest of the panels to be reused for anything from stairs to built-in or freestanding furniture.

More expensive upfront than more traditional alternatives, building with glulam or CLT is quick as well as fire resistant (as with logs, the timber chars). Also, with every surface structural and solid, there is no need to look for studs or insert plugs before screwing something onto the wall.

Guide Selfbuild

“

The big advantage of steel is its design flexibility.......

Steel

The big advantage of steel is its design flexibility, so if your house is a simple design, then steel probably doesn’t add up cost wise, but anything more adventurous than this and it’s worth investigating.

It is, for example, exceptionally easy (and thus comparatively cost effective) to create balconies and other structures that fall outside the building’s envelope. Steel frames are also a solution when working on uncertain ground, or when adding extra storeys to an existing building.

Warm frame construction, where the lightweight steel is enveloped in insulation in a way that ensures the dew point is outside the frame and thus minimises condensation, makes sure that nothing can rust.

The stick build method is what most people use (rather like a timber frame built from lengths of timber on site, only with light steel); there are also panelised systems, some of which can be pre-insulated and even have ties welded to the exterior surface to take brick or stonework. This type of system can be load-bearing, with the result that no rolled steel elements are

required at all and its strength means that concrete upper floors are simple, cost-effective to create and able to accept loads within a day or so of placing the concrete.

Good steel frame companies will take your design, do all the engineering calculations for you and deliver a steel package that

they, or others, can install. All the window and door openings are ready-made, and just about any level of pre-finishing complexity can be achieved to reduce work on site.

There is a cost for this, but it could be the difference between building during the winter or not.

Steel framing doesn’t need

SPRIN G 2021 / S EL F BU IL D / 117

BUILDING METHODS GUIDE / MODERN METHODS

Hempbuild, hempbuild.ie

treating with chemicals in the production process or later, (unlike timber), because it can’t become infested by worm or fungus, so no potential exposure to the chemicals that are sometimes emitted from treated timber.

Steel also provides very accurate dimensions, hard to achieve with masonry skin, and provides the widest spans possible.

Steel roofs are also possible for specific shapes but in most instances trussed roofs (timber) are used as they are more cost effective.

Eco blocks

Engineered clay blocks and hemp blocks are structural materials that provide strength and insulation.

As vapour permeable materials they allow moisture to escape all the while retaining heat within the walls. These tested and certified methods aim to take the hassle out of building with natural materials by providing a clear way for certifiers to sign off on your project. Compressed earth blocks are also factory made and offer similar advantages.

Hemp is usually combined with lime, which acts as a binder, hardener and preservative from rodents, fungi and microorganisms. As a finished material in walls, eco blocks are hygroscopic, which means they can absorb and release moisture to create an even indoor humidity, unlike many alternatives. They also have quite a low air permeability, one of the most important criteria in meeting our current building regulations. See also alternative building methods page 121.

Structural systems that incorporate factory fitted insulation can include a mix of materials; these often include fibreglass and/ or cement to provide strength and come in boards or kits that are 11 8 / SE LF B U ILD / S P R I N G 2021

ated systems and prefabric l ne pa , or e th of Many e coming from road and thos exit Br ve ha w come from ab no ill ugh, the UK w ods is transiting thro I the flow of go N In . ith w d ossing cr t bu to conten ed inue unhinder nt co eck to Ch . ed fs ct expe d tarif result in adde the border may r how they will be dealing lie with your supp and what additional fees n io at tu si with the able, if any. may be applic

Clayblock, clayblock.ie

Hybrid systems

The cost of Brexit

Guide Selfbuild

market offering vapour permeable insulation within a premade timber panel. These lock in together to form the walls.

As proprietary systems (unique to each manufacturer), the exact build up of these wall sandwiches will vary; some will include membranes to help with airtightness and humidity transfer for example. The build up will need to be checked by your independent certifier, be it your architectural designer or engineer to verify compliance with the building regulations.

passivehousing.ie

quick and easy to install on site.

Expanded Polystyrene (EPS) is the insulation used as the casing for ICF construction (see page 107) and is often used in hybrid systems too as it is lightweight, widely available and easy to work with. Even though it is not the best performing insulation, making it thicker allows it to achieve excellent U-values.

Another hybrid system is a wall panels made of hemp and lime that comes prefabricated and assembled as other SIPs systems.

Similarly, straw panels made in a factory are also now on the

Articles by Micah Jones, Andrew Stanway, Julian Owen, and Astrid Madsen

SPONSORED CONTENT

Ceramic Houses An energy efficient, quick and cost effective method to build your home.

The Ceramic Houses are made of ceramic lightweight concrete wall panels, which include proprietary silicate materials that are naturally fire proof (A1 fire rating) and provide excellent acoustic properties (45dB).

The wall panels, along with the roof structure, are made off site. All of the holes for electrics and plumbing, including ventilation ducting, are predrilled in the structure, as instructed on the construction drawings, before they arrive on site.

You can get the house built from a selection of house plans that the company provides, or supply your own drawings.

You can also either choose a shell only (internal and external walls, upper storey floor and roof) package or a turnkey option which includes

the kitchen, windows, roof coverings and internal and external finishes.

In the case of a shell only package, know that the manufacturer works to a 5-7mm tolerance, so there is no worry that the windows and doors won’t fit.

Quick and cost effective

Once the raft foundation is in place, Ceramic Houses will need two to four days to erect the walls. You will need a crane on site for the duration to lift the walls in place and then lift the roof trusses.

For a shell only build, the selfbuilder can start on the first fix electric and plumbing straight away, while the external insulation and roof finish is getting done by Ceramic Houses.

The walls are then plastered with breathable plaster on the inside

The walls are naturally energy efficient (U-value 0.2W/sqmK for 280mm wall, 0.14 W/sqmK for 340mm wall) and vapour permeable (µ = 23.4). ceramichouse.ie

and acrylic render on the outside; for the shell only option this is the responsibility of the self-builder to arrange. It is in fact quick to finish the walls internally as they can be directly painted or lightly skimmed.

For the turnkey option, Ceramic Houses will finish the house in two to three months depending on the specification. Prices for the shell only option start at €296/sqm.

SPRING 2021 / S EL F BU IL D / 119

s r o o d t ou BELFAST

SelfBuild Live is back & moving outside

Same great exhibitors - Same great advice Safer environment!

25th - 27th June 2021 - TEC Belfast

BUILDING METHODS GUIDE / OTHER BUILDING METHODS

Other building methods

DIY earth building

Earth based building components are made of subsoil, which is the inert (free of organic matter) layer beneath the topsoil. It consists of a mixture of gravel, sand, silt and clay. If topsoil is used instead, the integrity of the finished product will be compromised.

Earth building varies from region to region as each has been tailored to the type of soil available locally. Mixes were either applied in situ or dried in the shape of bricks and blocks, from the common clay brick to CEBs (compressed earth blocks, essentially rammed earth bricks).

To protect from the elements, the floor needs to be well insulated and the roof needs to provide cover past the wall in the form of an overhang.

Cob and rammed earth are two examples that can be used for floor and wall construction. In both cases the proportions need to be correct and when done on a DIY basis the only way to determine the right mix is by making samples

“

A lot of the subsoil found in Ireland has a high clay content, which is what is required for cob construction

P Walker, University of Bath

SPRING 2021 / S EL F BU IL D / 121

BUILDING METHODS GUIDE / OTHER BUILDING METHODS

and test walls, and consult with an experienced cob or rammed earth builder. The process is therefore cost effective (the majority of materials being free) but labour intensive and requires a basic level of know-how, as well as requiring an engineer or other certifier who is able to sign off on the project for building regulations purposes.

A lot of the subsoil found in Ireland has a high clay content, which is what is required for cob construction (15 to 40 per cent of the mix). Subsoil and straw, which acts as a reinforcing mesh, are mixed together with water to get an elastic consistency – a tractor can be used to make large batches. A timber frame may be used as a supporting structure but the walls can be freestanding, with round shapes a common feature of such buildings. Lime renders are common on external walls.

The rammed earth technique, on the other hand, is better suited to subsoil that has a lower proportion of clay (usually less than 15 per cent) and higher amounts of sand and gravel. Its roots can be traced back to China (think Great Wall), the Middle East and North Africa, especially in regions where the clay content was low and timber scarce.

Rammed earth is stronger than cob and less prone to shrinkage as the mix is compacted and requires less water; shrinkage and subsequent

cracks being caused by water evaporation. The build technique requires shuttering and tamping down (ramming down) to get the earth to compress to roughly half its volume; cement is sometimes added in what’s referred to as stabilised rammed earth.

The thermal mass of such construction can keep a house warm; earth walls have additional health benefits by managing moisture, lowering humidity and creating a pleasant atmosphere.

It is in fact feasible to build to nearly zero energy buildings Patrick Bradley Architects, pb-architects.com

12 2 / SE LF B U ILD / S P R I NG 2021

(nZEB) performance levels, as is required in ROI but this can only be demonstrated by building and testing real buildings, and oftentimes adding layers of (breathable) insulation. There are efforts underway to certify these types of buildings to nZEB standards, e.g. from a European funded project called CobBauge.

Shipping containers

Contrary to popular belief, building with shipping containers is unlikely to save you money. A simple reason is that the building regulations require that your home be insulated to a high standard, which will add to the cost by externally insulating (most expensive way of insulating, also removes the aesthetic) or reduce already precious internal room sizes. Small prefabricated homes may be a more straightforward and comfortable alternative.

Guide Selfbuild

Patrick Bradley Architects, pb-architects.com

“

Sourcing the shipping containers will be a hurdle and the likelihood is that you will buy new ones, to avoid having to deal with possible contamination issues.

New materials Inquisitive minds have put natural materials to the test, in particular mushroom roots. Mycelium There are structural implications too – if you make openings for essentials like windows and doors it will cost in steel reinforcement.

Ditto if the containers are not directly stacked on top of one another. So usually best left for a garden room if you like the aesthetic. Sourcing the shipping containers will be another hurdle and the likelihood is that you will buy new ones, to avoid having to deal with possible contamination issues.

is a material we’ve covered in Selfbuild magazine before, in its use as an insulation material, but architectural practices in the USA are also developing structural panels made of the fast growing fungus. One project availed of

existing waste board material and used the mushroom to glue them back together. Another is creating engineered, interlocking panels.

Recycled plastic blocks, meanwhile, are also in the developmental phase, for use in retaining walls.

“

Inquisitive minds have put natural materials to the test, in particular mushroom roots.

Bamboo The timber you get from your

timber frame supplier and builder’s merchant will be softwood that is treated and graded for strength.

Bamboo, which is technically a grass, is treated in a similar fashion to build homes. Its compression and tensile strength are comparable to mild steel and concrete. Bamboo homes can be bought prefabricated but are rare in Ireland.

Information compiled by Astrid Madsen

SPRING 2021 / S EL F BU IL D / 123

BUILDING METHODS GUIDE / THERMAL BRIDGING

Hidden danger To reduce running costs, homes are built so that they retain as much heat as possible. This fabric first approach focuses on getting the insulation, airtightness and structural components to act as an effective buffer against the elements. After poor airtightness, one of the greatest enemies in the struggle to build a near zero energy building is what’s known as thermal or cold bridging.

Words: Mark Stephens MRIAI, markstephensarchitects.com

What’s invisible yet can cause enormous damage and discomfort to your building and the people living in it? Thermal bridges, which are places in your house where heat escapes, rather than where cold air infiltrates. These losses can only be detected after construction with the help of an infrared camera (see Thermal imaging on the next page).

You not only need to specify the right kind of materials, insulation and construction, you will need to identify where the thermal bridges could occur and put measures into place to avoid them. It typically happens at the junctions between plane building elements, e.g. at wall/roof and wall/floor junctions, and around openings, e.g. at window jambs and other areas where the continuity of the insulation is interrupted.

Heat loss happens both through such gaps but also through gaps between insulation. So as well as the details shown below, you will need to ensure that there are no gaps between your insulation sheets or batts as these gaps are also a cold bridge from the outside to the interior.

You can do this by installing them in layers, with the joints staggered. What you are trying to achieve in this instance is to eliminate any cold air circulating freely on the warm side of the insulation; the technical term for this is a Thermal Bypass.

Note that you will need the assistance of someone who is trained to produce thermal detailing in the construction drawings; it isn’t a DIY job. And in order to use these thermal bridge calculations in your BER/SAP report. The person who prepared them will need to be properly accredited – in ROI there is a Thermal Modellers Scheme where each member is accredited with the National Standards Authority of Ireland.

Construction stage Crucially, once you have detailed the measures to put in place at the 12 4 / SE LF B U ILD / S P R I NG 2021

design stage, you need to make sure that the instructions are followed through during construction.

It is no longer acceptable for a builder to say “ah, that’s the way we do it around here”; knowledge is power and it is up to you to ensure that your builder constructs your house without cold/thermal bridges.

The key aspect to remember in all of the following details is that for thermal insulation to be effective, it needs to be continuous. As with airtightness, the aim is to maintain a continuous envelope of insulation at junctions on the plans and elevations.

Last but not least, cold bridging will also happen through conductive materials such as blockwork, concrete slabs or steel, so when used in the build up and where they break the insulation envelope, you need to insulate around them – either on site or by buying the materials pre insulated.

Guide Selfbuild

Thermal imaging To measure how airtight your home is, you will need to carry out a blower door test, which is mandatory in both NI and ROI. The test is done at the end of the build to certify that it passes the airtightness requirements of the building regulations. If it fails the test, remedies can be costly as they will involve removing layers of finishes to get at the problem area to fix it.

This is why an airtightness test mid-build to test installation is progressing as it should, can be a good idea, to check problems before they are boarded up.

Thermal imaging is a visual way of identifying where air leakage is happening, and is often used in existing homes to identify problem areas.

When looking internally, colder colours such as blue indicate a lower temperature, i.e. where heat is escaping/cold air entering. In new builds thermal imaging will visually show that work has been carried out according to the thermal bridging specifications. The opposite is true when looking externally where the brighter reds, oranges and yellows indicate heat escaping. The scale is in degrees Celsius, with 20 degrees commonly considered a comfortable indoor air temperature.

The example here shows a lack of thermal bridging measures at the junction between wall and floor, and between the window and wall.

At floor level Subfloor

Between floor and wall

Thermal bridging can occur between the foundation and rising walls (blockwork underneath the ground that links up with the ground wall construction above).

The blocks used for your rising wall will need to be thermal blocks

to prevent a thermal break. These thermal blocks should be used in the inner leaf rising wall aligned with the floor insulation; this will reduce the thermal bridge through the inner leaf.

As well as the foundation detail you will also need to consider

creaghconcrete.co.uk - Spanthern Thermal Floor

The first stage to reduce the cold bridge at foundation level is the adoption of an insulated foundation system. The principle is similar to Insulating Concrete Formwork (ICF), where polystyrene is used as formwork for poured, mass concrete walls. Instead in this instance the polystyrene is used as formwork for the foundations. By adopting a system of this type you can reduce the U-value through the foundation down to 0.1 W/sqmK (the Passivhaus standard is less than 0.15 W/sqmK).

Even though you can achieve this with a conventional floor build up, insulated foundations offer the added benefit of reducing the volume of concrete required for the foundations and floor slab.

Without insulated foundations, a good subfloor detail would need to include a substantial thickness of insulation under the floor screed;

at the very minimum 150mm of rigid foil-backed PIR board. If building a cavity wall using partial fill insulation, make sure that the insulation in the wall continues below the floor by a minimum of 225mm.

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BUILDING METHODS GUIDE / THERMAL BRIDGING

Window specification to reduce thermal bridging An easy example to see a thermal bridge at work is in a single glazed window, where the heat in the house is transferred directly to the outside via the single pane of glass. On a cold day you will see the cold bridge as condensation appearing on the inner surface of the glass.

Thermal bridging increases heat loss through the fabric of the building and in some cases results in surface, or interstitial condensation, which can in turn lead to mould growth.

We can immediately see the benefit of using double or triple glazing over single (although despite great advances in glazing technology, a wall will always perform better than a window!) but in terms of thermal bridging the frame is also crucial.

For this the windows and doors must be “thermally broken�, that is there needs to be an element of low thermal conductivity between the inner and outer frames to prevent the temperature outside to transfer through the frame.

This problem is particularly prevalent in metal windows or curtain walling as these materials are better at transporting heat.

In a residential setting old aluminium windows are among the most notorious at letting heat through; when buying new ones, a resin thermal break will be present both in the casement and in the frame in order to prevent cold bridging. In timber or uPVC windows this is not required as their thermal conductivity is much lower.

With regards to the width of the spacer bars (space between the double or triple glazing frames) it will typically depend on the type of gas inserted between the glass.

12 6 / SE LF B U ILD / S P R I NG 2021

the junction of any floor screed to the external wall, where you should install perimeter insulation (often 25mm PIR insulation board which come in strips 150mm high, installed upright). Make sure that any insulation under the floor screed is tightly abutted to the blockwork wall.

You will also need to consider upper floors; if it is a concrete precast slab you are using, then you will need to ensure it sits on the wall without compromising the continuity of insulation in the cavity.

Around windows & doors Above the openings

At window and door penetrations you will need to consider the junctions in both plan and section drawings. At the top or head of the opening, there will be a lintel supporting the weight of the wall above. All gaps between two concrete lintels needs to be tightly filled with insulation or better yet with a purpose-made insulated cavity closer. In the case of steel

Guide Selfbuild

lintels, the steel plates should be separated to create the thermal break and the area between should be filled with insulation. Preinsulated steel lintels are ideal.

Below the openings

Window sills close the openings at the base. To avoid any issues, best again to go with a preinsulated product which in this case is the insulated sill, whose core consists of an insulation board. Insulated sills deal with thermal bridging but are also lightweight and therefore easier and safer to work with.

If you are instead using a concrete sill, it needs to be thermally separated from any interior concrete/plaster by a strip of insulation and proprietary

insulated supports can be used to support it.

If you are using partial fill insulation batts then you need to ensure that the insulation is firmly secured against the inner leaf of the cavity wall. The sill must not cross the cavity and should not rest on the inner leaf.

Around the openings

Cavity closers will deal with thermal bridging at the sides.

These are installed at a right angle to the insulation that is tight up against the inner leaf of the cavity wall.

At roof level

Weak points at roof level are typically at the eaves junction of

the roof to the external wall due to the requirement of closing the cavity to stop fire spread and also at the gable where the inner leaf rises from the warm rooms to the cold attic.

These are often dealt with proprietary fire-proof cavity closers which provide a continuous insulation barrier.

At balconies

A conventional balcony that extends from inside to outside is particularly prone to thermal bridge problems, as it consists of a slab that cantilevers from the house that is not separated thermally from the main building.

It is essential to create a thermal break; there are products

on the market that are devised to deal with thermal bridges at concrete-to-concrete, concrete-tosteel and steel-to-steel junctions.

The Passivhaus standard recommends using freestanding balconies that can double up as shading devices for non-northern facing windows on the ground floor, to prevent overheating in the summer.

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BUILDING METHODS GUIDE / BUILDING THE DREAM

Choosing how to build our house

Brian Corry

My wife, Karen, and I spent lots of time looking at the different building methods on display at the Selfbuild Live events. We were faced with some genuinely tricky choices but, like most self-building decisions, it boiled down to personal preference and our own individual priorities, writes self-builder Brian Corry who's on a mission to build himself an eco house.

Everyone knows the story of how the three little pigs built their homes out of straw, sticks and brick, and that the only one the big bad wolf didn’t blow down was the masonry structure. It is, of course, just a fairy tale but culture and tradition still hold sway in Ireland when it comes to choosing building methods.

Of course the availability of stone and brick versus the relative scarcity of wood meant previous generations didn’t really have much of a choice. But today, modern techniques even allow materials such as straw to be used.

On the menu

Traditions take time to change yet self-builders are, and always have been, by their very nature pioneers.

Our approach, therefore, was to keep an open mind. And so in addition to brick/block, we looked at timber frame (built off site), insulating concrete formwork (ICF), structural insulated panels (SIPS), cross laminated timber (CLT) and glulam (glued laminated timber).

Reassuringly, we knew that whichever system we chose it would do a good job. But we had other criteria which helped narrow down our options.

In 1840 the three little pigs would not have been concerned with airtightness but today we now know how big an impact it has on a home’s overall thermal performance.

This was very high on our priority list for we wanted a home 12 8 / SE LF B U ILD / S P R I NG 2021

that would lose a minimal amount of heat, and which in turn would significantly reduce the amount of heating we would need. Helpfully, most modern building methods lend themselves to achieving good airtightness – although it can a bit difficult with brick and block.

Self-building is a steep learning curve and a conversation with a timber frame supplier at Selfbuild Live Belfast got us to research the

topic of vapour permeability.

This particular supplier felt that homes needed to be both vapour permeable and airtight and used the example of wearing a bin liner versus wearing an all-weather jacket when going for a walk. A bin liner won’t let water, vapour or wind, either in or out, leaving you very sweaty but in contrast a “breathable” jacket will let the moisture vapour escape but keep

the wind and rain out.

After doing some further research we understood that modern ventilation systems, correctly sized and fitted, were capable of providing the required amount of fresh air however, we felt that it was desirable to also have a structure that allowed vapour to escape naturally whilst still being airtight, all of which started to push us towards wood.

Guide Selfbuild

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Traditions take time to change yet self-builders are, and always have been, by their very nature pioneers....

iDomus Engineered Timber Construction, idomus.ie

SPRING 2021 / S EL F BU IL D / 129

BUILDING METHODS GUIDE / BUILDING THE DREAM

Insofar as possible Karen and I were very keen to use materials that were both low carbon and natural – but a word of warning.

Once you start down the route of something like achieving vapour permeability then it will have a knock-on effect on many specification decisions.

For example, there is no point using a permeable structural material if non-permeable insulation is then used to wrap it, for it will act as a barrier to any vapour escaping. Fortunately, there are now quite a few natural insulation products like sheep’s wool, wood fibre insulation and rockwool to name just a few.

The glulam choice

From an ecological and carbon footprint point of view we were keen to use as much wood as possible and found the solution at Selfbuild Live Belfast. The House Building Element (HBE) glulam building method, devised and manufactured by a reputable German company, fit the ecological bill perfectly.

Glulam, which is engineered wood, is a structural material so it is capable of carrying large loads without the need for steel or other reinforcement. In addition, as it is solid timber, it gives the same solid feel as a concrete, brick or block built home.

The first floor is also solid timber which means that there is very little noise transfer from upstairs, and similarly it gives excellent sound attenuation between rooms, which we felt is important. From a fire rating perspective, it also scored well as it chars rather than burns due to the wood’s density.

Speed of build is often cited as one of the main advantages of modern building systems and this was a key advantage with HBE. The climate in Ireland is so changeable that having a building system that is not overly weather dependent can be a key advantage.

The HBE structure we were looking at could be built in the rain in two weeks. It also doesn’t require any 13 0 / SE LF B U ILD / S P R I NG 2021

large lifting machinery as each piece can easily be lifted by two people.

There is no cutting required on site as each piece, including the stairs, comes from the factory at the right size so essentially the whole thing interlocks and is screwed together on site. The wood fibre insulation is then screwed to the exterior followed by the cladding. Assembly does not require a large degree of skill, a straightforward task for any competent joiner.

The fact that you can drill and screw directly to the timber leads to considerable time saving at first fix stage, which is when the plumber and electrician run their cables and ducting. The walls can be quickly routed to carry the conduit for the sockets and the cables, and wires are clipped to the underside of the wooden first floor.

A key selling point for us with the solid timber walls was that it will make it very easy for us to hang pictures, attach brackets, etc. without having to use specialist attachments or in the case of timber frame, having to locate studs.

Similarly we plan to dryline the walls, whereby the plasterboard is simply screwed on and taped together ready for painting. This means we won’t have to wait for plaster to dry, further speeding up this stage of the process.

At the end of the day, the speed of build is down to the number of people you decide to employ. We allowed two weeks for the main structure and a further two weeks to get the house weathertight, i.e. roof on and windows and doors in.

The window openings come with a 2mm factory tolerance, so it is entirely feasible to order the windows in advance. We plan to start the first fix one month into the build, at the same time as we attach the insulation and cladding externally.

Cost comparison

So what does it cost compared to the alternatives we looked at? This was clearly a big consideration and

there is no hiding that building our house in solid timber was going to cost more upfront. That said, we will be saving money throughout the build due to speed and reduced labour costs.

Brick or block or a very standard timber frame would have been the cheapest way to go upfront, but we were aware that it would be both harder to achieve an airtight structure and ensure an unbroken insulated thermal envelope with no cold bridges.

A high quality, vapour permeable timber frame using similar eco materials or ICF would also have

worked out slightly cheaper, but we wanted both solid timber for its mass as well as vapour permeability.

Whilst we weren’t looking to build a passive certified house, we did want to build something that would require as little heat as possible, and that’s what we will achieve. The U-value of our roof is 0.14W/sqmK, the floor 0.15W/sqmK and the walls 0.16W/ sqmK. Together with triple glazed windows with a U-Value of 0.7W/ sqmK, the heat requirement will be minimal.

more indvdualty.

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