Green Roofs + Vegetated Building Surfaces

GREEN ROOFS

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VEGETATED BUILDING SURFACES RESEARCH, ANALYSIS & PROPOSAL JARED POHL

Cover and Left: Nashville Music City Center Image source: author

CONTENTS INTRODUCTION: THE TOP OF THE BUIDLING

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ROOF GARDEN PROPOSAL: UTK COAD

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RESEARCH: ANNOTATED BIBLIOGRAPHY

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COOLER BUILDINGS STORMWATER MANAGEMENT IMPROVING QUALITY OF RUN-OFF EXTENDING THE LIFE OF THE ROOF MEMBRANE REDUCED HEATING & COOLING LOADS ENVIRONMENTAL IMPACT OF ROOF CONSTRUCTION OPPORTUNITY FOR URBAN WILDLIFE REFUGE ASSET TO URBAN AGRICULTURE ASSOCIATED COSTS AMENITY VALUE & INCREASED REAL ESTATE VALUE LIVING WALLS - VERTICAL SYSTEMS

CONSTRUCTION & SPECIFICATION

BIBLIOGRAPHY

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PRECEDENT ANALYSIS: ASLA HEADQUARTERS

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ARCH 593 STUDENT: JARED POHL ADVISOR: JAMES ROSE

University of Tennessee College of Architecture + Design Image source: author

THE TOP OF THE BUILDING

The research component of this text explores the many quantifiable positive effects that vegetated surfaces can have on an architectural space if selected properly. By applying the outlined tactics to the extreme environment of a roof, we are able to increase the usable space of our buildings in a way that is pleasant to occupy. The symbiotic nature of vegetation also has a profound affect on many forward thinking sustainable design topics.

Thus we make buildings environmentally friendly with healthier spaces, and we take advantage of an additional floor plate of square footage.

The design proposal is rooted in the spirit of modernism. It continues Le Corbusier’s conversation about roof gardens and is meant to realize the potential for Knoxville’s most prestigious modernist building, Bruce McCarty’s University of Tennessee College of Architecture and Design. The task of the proposal is to reclaim the flat roof, which in today’s practice is typically abandoned to the engineer, and create a garden with access to fresh air, sunlight and views of our campus. The roof has almost no identity associated with it, thus it inherently has a great opportunity for advancement through design.

A narrative of the basic elements of architecture, according to Simon Unwin (Analyzing Architecture, 37), includes a roof or canopy as an element that “divides a place from the forces of the sky, sheltering it from sun or rain. In so doing, a roof also implies a defined area of ground beneath it.” It is generally understood that a roof is the component of architecture that creates shelter, but it is precisely this generic understanding that this investigation explores.

Lets begin at the beginning. On the primitive hut we see a triangular geometry on top of a defined space, a pitched a roof.

Dating back to the primitive hut, the roof is a system of structural members leaning against each other for support and bound at the peak. This form harnesses the structural integrity of a series of members and works as a system to create shelter.

We move forward in history looking at the roof synchronically as the evolution of components and form. We still see that same basic form on top of most of our buildings, but it has become more intrinsic. The arch is developed as a series of segments that support one another. If the quantity of these segments increases around a revolved pattern we can create a dome.

For centuries we capped our buildings with triangular and dome roofs. But a revolutionary new building system arrives and now we can pour our roofs out of reenforced concrete. With the reenforced concrete roofs we need very little pitch. The roof garden, explored by Le Corbusier, challenges the preconceived notion of the roof.

“By suppressing the roof and replacing it by terraces, reinforced concrete is leading us to a new aesthetic of the plan, hitherto unknown.”

Le Corbusier (Towards A New Architecture, 63).

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ROOF GARDEN PROPOSAL THE UNIVERSITY OF TENNESSEE COLLEGE OF ARCHITECTURE + DESIGN

AERIAL DIAGRAM OF PROPOSAL 2

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SOLAR GARDEN STAIRWAY LOUNGE AREA LAWN RAISED SEATING OUTDOOR PIN-UP SPACE VIEWING PLATFORM ELEVATOR EXTERIOR STAIR

PLAN VIEW OF PROPOSED ROOF GARDEN

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PERSPECTIVE VIEW OF LAWN UNDER CANOPY

PERSPECTIVE VIEW OF OUTDOOR PIN-UP SPACE

PERSPECTIVE VIEW NEW CIRCULATION AND LIVING WALL 7

SEMI INTENSIVE

LIVING WALL

EXTENSIVE

BUILDING SECTION 8

INTENSIVE

EXTENSIVE

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SECTION CUT THROUGH COURTYARD 9

AERIAL DIAGRAM OF PROPOSAL 10

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RESEARCH

“Our health, both as human beings and as one of the millions of species in nature, depends upon the air that we breathe and the water that we drink, as well as on the uncontaminated quality of the soil from which our food is produced. In the coming decades the survival of humanity will depend on the quality of the natural environment and, crucially, on our ability to continue to carry out all our human activities – without further impairment and pollution of the natural environment. Simply stated, our health as human beings depends on the continued health of our natural environment.” Ken Yeang (Hart, page 14)

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Intensive Green Roof at Peggy Notebaert Nature Center, Chicago

Image source: author 13

Image source: Seward, page 50

Image source: Stever 14

COOLER BUILDINGS IN THE SUMMER A positive effect of green roofs is the lowering of temperatures in the areas surrounding the vegetation. After a rainfall, there are two separate processes occurring that result in the lower temperatures. The air and wind moving across the soil results in evaporation of water, and consumes the energy. Also the plants are discharging water vapor through photosynthesis and transpiration. The combined effects of the evaporation and transpiration are known as evapotranspiration. An inherent result of evapotranspiration is evaporative cooling.

Evaporative cooling uses energy to turn water from liquid into vapor, thus resulting in lower ambient temperatures.

The lack of vegetation limits the potential of evaporative cooling for conventional ballasted roofs. While these ballasted surfaces are consuming energy to evaporate water, they are at a severe disadvantage to planted systems because they do not store rainwater and they lack the transpiration abilities of living roofs. The foliage of a green roof blocks the UV radiation of the sun. “Increase in foliage density lowers the temperature at the soil and vegetation surfaces,” (Ouldboukhitine, 2630). The vegetation results in a lower air temperature on a roof. This lower air temp can result in higher efficiencies for cooling equipment, and higher efficiencies for PV systems (Castleton, 1586).

Green roofs are not static in there thermal conductivity. When moisture is introduced, which is required for the success of the living roof, the thermal conductivity is altered and becomes more conductive to heat loss/gain, (Ouldboukhitine, 2625). This increased thermal conductivity can be maximized in situations similar to a trombe wall. It is possible to saturate the growing surface at night when the outside temperature is lower, in order to pull undesired heat out of the building resulting in a lower temperature without the energy consumption required by an air conditioner.

Image source: Kohler, pg 1442

The efficiency of photo voltaic panels is increased when assembled on green roof. By reducing airborne pollutants and lowering the ambient temperatures around them, plants boost the efficiency of solar panels by 3% - 16%, (Weaver, 1). The shade created by the panel has a symbiotic affect, in that it allows broader leaf plants that require shade to survive in the shadow. Also, there is a “synergetic effect of planted roofs in combination with photo voltaic installations: increase in efficiency of PV plant, since the ambient air temperature on planted roofs – max. 35 C (up to 90 C in the case of asphalt roofs) – inhibits the modules heating up and thus prevents a drop in performance. Threeyear trials found that the gain in performance can amount to 4 percent,” (Kohler, 1442).

“Studies at Chicago City Hall have determined that the greening of the roof lowered the air temperature on the roof in summer to 85 F as compared to 110 F on a typical black-tar roof,” (Seward, 55).

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“Each type of green roof lowered roof temperatures during warm weather by 30 C – 35 C, compared to the black roof…The white roof, as expected, was cooler than the black roof but by a much smaller margin,” (Wilmeth, 1).

“When the roof is frozen, the insulation role of green roofs is effective, but their performance doesn’t differ significantly of those of conventional roofs in the presence of snow,” (Ouldboukhitine, 2625).

“The green roof has been as much as 32 degrees cooler than conventional black roofs on neighboring buildings,” (ASLA Green Roof Monitoring Results).

“The lack of heat buildup on a green roof has therefore been suggested to increase the efficiency of air-cooling and ventilation systems,” (Castleton, 1586).

“Temperatures on the ASLA roof differ by area – areas with thicker growth and better coverage are cooler,” (ASLA Green Roof Monitoring Results).

If implemented on a broad scale, they have the potential to reduce the urban heat-island effect.

Parks and green spaces in the city result in lower temperatures through evapotranspiration and shading from vegetation, (Snodgrass, 34).

Extensive Green Roof at Peggy Notebaert Nature Center, Chicago

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Image source: author

STORMWATER MANAGEMENT Conventional construction methods for buildings shed rainwater by directing it to downspouts and overflows. The thought process is that we need to get the water off the roof as soon as possible in order to save the building, when the realization is we’re causing major heath and infrastructure problems for ourselves at the ground level. One of the main causes for the lack of attention being paid is that the problem is out of sight, so it is also out of mind. Let’s identify the problems here. First, we are letting a very valuable natural resource slip through our fingers. The stormwater we’re trying to get rid of is freshwater that could be charging our water tables, irrigating our plants, and even supplying us with a plentiful and inexpensive water source for our laundry machines and toilets. As Snodgrass stated: “Without porous surfaces through which it can filter through soil and recharge groundwater, stormwater becomes a problem rather than the replenishing resource it should be” (Snodgrass, 27).

Second, we are fighting Mother Nature with civil engineering. Traditionally we have utilized combined sewer systems to transport our waste water and stormwater to the treatment facilities.

As our towns and cities expanded and grew in population, it was quickly realized that there was a massive underestimate for the amount of water that would need to be treated during storm events. The problem is that the rain is rushed down and away from our buildings as soon as possible, so instead of having our treatment plants clean and discharge water from a garden hose over a period of say 20 hours, we’re dumping Niagara Falls into them for 5 seconds.

This causes massive overflows of raw sewage into fresh water sources such as rivers, creaks and streams and destroys environments. Our decision to continue bandaging our combined sewer systems is wasting resources and money.

Of the 65 precipitation events that occurred during the monitoring period in Washington, DC, only 15 were capable of breaching the green roof at the ASLA headquarters. 55 of these events, or 77% of the time, there was zero runoff. The stormwater management infrastructure was only required 23% of the time, (Glass, 5).

GRAPHIC BY AUTHOR, BASED ON DATA FROM ASLA REPORT 17

“In 2004, the EPA reported 850,000,000,000 gallons of untreated sewage and stormwater in 32 states and DC every year. These Combined Sewer Overflows (CSO discharge) are a result of the increased strain put on antiquated stormwater management infrastructure.

In NYC alone there are 460 CSO discharges every year, which result in 27,000,000,000 gallons of untreated dumping (Snodgrass, 27).”

In order to have our civil engineers design and build an infrastructure that will separate the remaining combined sewer systems in America, the EPA estimated (in 2005) that it would cost about $55 billion. The infrastructure problem of combined sewers comes with a hefty price tag of an EPA estimated $55 billion (2005 dollars) of capital improvements, (Glass, 5). The EPA isn’t going to wait around for things to break down either. They initiated the: EPA Clean Water Act: 2007 Energy Independence and Security Act, Section 438 (Snodgrass, 41) Approach 1: Infiltration, evapotranspiration, harvesting and reuse of rainfall prevent runoff.

Approach 2: Maintain pre development rate, volume, duration and temperature of runoff (EPA 2009b) We need to put the green back into the built environment. If we make the roof permeable again we’ll attenuate the peak flows that enter the stormwater management systems. By slowing and moderating the amount of water that enters the sewers, we can ensure that our systems don’t spill sewage into our downstream neighbor’s water supply.

Here’s how we do it. Living roof vegetation minimizes the runoff and intensity of heavy rain events by releasing rainwater in a slower, more evenly dispersed fashion. This also reduces the amount of water on the ground through evapotranspiration (evaporation and transpiration). (Snodgrass, 28).

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“The amount of water lost by [evapotranspiration] is a combination of the amount of water lost by the plant transpiration and the amount of water lost by soil evaporation,” (Ouldboukhitine, 84). “[of six green roof designs] the most effective green roof captured about four times as much water as the least effective, which did little better than the conventional roofs. Substrates with large planting-medium retention cups, low drainage-hole area in the drainage layer, and a high proportion of perlite in the planting mix correlated with high water retention,” –Mark Simmons, Ph.D. (Wilmeth, 1).

We can also drastically reduce the amount of stormwater to about 25%. The study period for the green roof at the ASLA headquarters in Washington, DC went way longer than was expected. The study was focusing on the quality of the runoff leaving the roof. The monitoring period for run-off quality was longer than expected, because 75% of the rainfall never left the green roof. It was released back into the atmosphere through evapotranspiration, (Glass, 2).

“The total volume of runoff leaving the roof was reduced by 74% (9,725 of 37,237 gallons),” (Glass, 6).

“The roof retained more water during the growing season. In Sept. 2006 – the heaviest month of rainfall – the roof retained 79.5 % of the 5.56 inches of rain. In November 2006, the roof retained 58.9 % of 4.35 inches that fell during the month as the plants were dormant,” (ASLA Green Roof Monitoring Results).

The Scum Line of Second Creek in Knoxville, TN Image source: author

IMPROVING RUN-OFF QUALITY Water is pouring of the roof tops, squirting out of downspouts and turning the street into a river. With the sheetflow of storm water goes all the gas, oil, dirt, dust, heavy metals, heat, cigarette butts and garbage that laced the streets. The urban canal finds a low point in the topography and drops off at the stream or river.

All the pollutants, grime and chemicals from a single urban tributary join the countless other tributaries of similar conditions. The hot murky nastiness of the built environment wreaks havoc on the riparian ecosystems, creating dead zones and leaving traces of trash everywhere.

Green roofs help minimize the transmission of pollution by reducing the amount of runoff at street level. Green roofs are classified as a form of Low Impact Development (Univ of Ark) which is a soft engineering of stormwater management,

verse the hard engineering tactics of pipes and holding tanks that is currently employed.

Green roofs, in combination with bioswales and water treatment parks at street level, will reduce the contamination levels of our waterways and restore them as ecological habitats. Because of the reduction in quantity of stormwater runoff, green roofs prevent “flooding, erosion of stream banks, increased sediment loads, higher water temperatures in the summer months (5-12 deg.

F), (Snodgrass, 26).

“Address the change in storm water quantity and quality by applying run-off factors for pollutants to the different roof types [ballast, extensive, intensive] to calculate the potential reduction of pollutants released to water due to the reduction in the run-off,” (Kosareo, 2607).

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The tested water samples at the ASLA headquarters were less available than the team had hoped for, because there were so few instances which any runoff water was even available to test. Of those samples that were tested, “most of the parameters measured were within the allowed freshwater chronic concentration values promulgated by the EPA,” (Glass, 10).

The data from Dr. Glass’ tests shows that there were consistently more total suspended solids (TSS) and total dissolved solids (TDS) in the runoff that was collected, than there was in the rainwater. Although the concentrations were higher, it is important to remember that there was a drastic reduction in the overall amount of runoff generated. So “when combined with the measured volume reduction, a significant reduction…can be expected from a green roof.”

(Glass, 18).

A reduction in the frequency and the amount of stormwater at the street level will reduce the flow of contaminants downstream. This does not address the problem of runoff contaminants accumulating, but that can be mitigated through LID (bio-swales and stormwater treatment parks.

“Once you have a full canopy developed that’s three to four years old, and it’s matured, you’re looking at probably a 95 percent reduction in the solar load.”

David R. Tilley University of Maryland Department of Environmental Science and Technology (Millard, page 56)

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EXTENDING THE LIFE OF THE ROOF MEMBRANE The plants and soil of green roofs have an insulating quality. They prevent UV rays from hitting the roofing membrane, (Snodgrass, 31).

Heat is transferred through radiation by UV rays. By creating a canopy, a vegetated roof shades the soil and reduces the transmission of radiated heat waves that come from the sun’s rays. The plant cover drastically reduces the amplitude of the temperature fluctuation and reduces the thermal stress exhibited on the roofing membrane. This reduction prevents degradation of the membrane and results in a longer life cycle for the roof.

Roofing membranes that are replaced every 15-20-25 in conventional construction, are able function longer. “Intensive planted green

roofs in Portland have been leak free since construction in 1975, (Snodgrass, 31).

“For most extensive green roofs the expected life span of the roof system is expected to be 25 years…research shows that green roofs can protect the roof membrane upward of 50 years, (Kosareo, 2608).

“The roof membrane peak temperatures were reduced by the green roofs and delayed from around 2 pm to 7 pm,” (Castleton, 1584).

“Green roofs protect the roof membranes from extreme temperatures during hot days and high temperature fluctuations by reducing thermal stress,” (Ouldboukhitine, 78)

REDUCE HEATING & COOLING LOADS

Roof to wall ratio – The higher the ratio, the more significant the impact can be (Snodgrass, 32).

A living roof is a “dynamic system,” where many combinations can achieve a variety of results (Snodgrass, 32). i.e. moisture and air content, biomass, etc.

Insulation properties of the living roof reduce the heat flow through the roof (Snodgrass, 32).

“Planted roofs suffered less heat gain during the day; hence this effect was much less. By measuring the air temperature at various heights above the green roof it was found that after sunset the ambient air temperature above the vegetation was reduced significantly and continued to cool the ambient air throughout the night,” (Castleton, 1583).

Image source: author 21

(steel deck with thermal insulation above) “By measurement they found that the heat gain through the green roof was reduced by an average of 70-90% in the summer and heat loss by 10-30% in the winter,” (Castleton, 1583).

DOE EnergyPlus – Program developed to model “radiative heat exchange, convective heat transfer, soil heat conductance and storage, and moisture effects” of green roofs [ecoroof option], (Castleton, 1586).

“For most commercial buildings, the additional loads associated with an extensive green roof (typically about 120-150 kg/m2) do not require any additional strengthening,” (Castleton, 1587).

“Older buildings with poor existing insulation are deemed to benefit most from a green roof as current building regulations require such high levels of insulation that green roofs are seen to hardly affect annual building energy consumption,” (Castleton, 1582).

Green roofs using rubber crumbs as the drainage layer recorded higher energy consumption levels than similar green roofs that used volcanic gravel as the drainage layer.

The study recorded lower internal temperatures on the structures that used the rubber crumbs, because they consumed more energy, (Pérez, 457).

Green roofs manage solar radiation more efficiently because of the reflective properties of the vegetation, (Ouldboukhitine, 2624).

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Castleton suggests the possibility of the reduction in ambient temperatures on the roof can extend the seasonal efficiency of ‘free cooling’ for load dominant buildings. It may even be possible to use the thermal consistency of the growing medium to implement some sort of geothermal system.

“The presence of a green roof on a building improves thermal comfort since it lowers the soil temperature, (Ouldboukhitine, 2630).

An “engineering analysis showed that the green roof created a 10 % reduction in building energy use during winter months,” (ASLA Green Roof Monitoring Results).

“The temperatures of the different layers of a double-skin façade are generally lower if plants are used instead of blinds in the interior space…the plants surface temperature never exceeds 35 C, while in blinds it can exceed 55 C. The installation of plants inside a double skin façade reduces energy consumption by air conditioning systems by up to 20%,” (Pérez, 4856).

A green wall covered in ivy “reduced the peakcooling load transferred through the west-facing wall by 28% on a clear summer day,” (Pérez, 4586).

“Protecting the building from the cold wind with vegetation (green roofs and walls), reduces the heating demand by 25%,” (Pérez, 4857).

LOWER ENVIRONMENTAL IMPACT OF ROOF

Life Cycle Assessment (LCA) compares the environmental aspects and potential impacts associated with constructing, maintaining, and disposing of a 1115m^2 roof (Kosareo, 2607).

The fact of the matter is that the embodied energy in the production of our conventional low-slope roof membranes can maximized (doubled or tripled) by providing a significant layer of protection (green roof).

Recycled materials, such as rubber crumbs for the drainage layer, result in the same performance as conventional materials (PĂŠrez, 354), but require less embodied energy to

Intensive Green Roof at Millennium Park, Chicago

produce.

Using rubber crumbs is more environmentally friendly than using volcanic gravel. The same method can be applied for the actual growing medium used. The typical recipe for a growing medium contains a large portion of either expanded clay or expanded shale.

These can be obtained from recycled masonry.

An unwanted cube of bricks can be crushed and re-purposed as the growing medium for a green roof. This tactic takes advantage of the embodied energy already spent on the production of brick, while also finding a use for reclaimed and excess materials.

Image source: author 23

CREATING A PROTECTED WILDLIFE REFUGE

Living roofs provide an opportunity for biodiversity, which is important to remediate in urban areas. Habitat driven projects exist in London, such as the Black Redstart bird refuge, (Snodgrass, 36).

“If [the client] ecology, plants have pollen for good structure 52).

wants to establish an must be chosen that insects and birds and for spiders,” (Seward,

Vancouver’s Convention Center is a large example of green roof that hosts an ecology. The roof is in the downtown area of Vancouver and is 261,360 SF. It is a artificial habitat for plants, birds, mice and 250,000 bees in hives. (Seward, 53).

Image source: author

ASSET TO URBAN AGRICULTURE

Whittinghill et al’s study tested vegetable production against in-ground conditions, extensive green roof conditions, and raised planters on a roof.

“One of the biggest challenges facing inground urban agriculture is the availability of land,” (Whittinghill, 466). The economic value of urban land is high due to the potential for real estate development. This often squashes any opportunity for urban agriculture.

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Whittinghill’s study documented the production of vegetables over a period of 3 years (20092011). They found that by utilizing slow release fertilizers and irrigation, an extensive green roof “was as good as if not better than their performance in-ground,” (Whittinghill, 480).

Over the three growing seasons, it was actually the variation in weather that caused a noticeable impact on the production of the vegetables.

COST

The idea of cost needs to be expanded beyond the roof component. Think about the engineering requirements of stormwater detention for the site. (Snodgrass) “A reasonable estimate to retrofit extensive green roof would appear to be around 150 pounds / m2 (at 2010 prices),” (Castleton, 1588). This converts to $21.46 / SF. “We did a life-cycle cost analysis of a green roof versus a regular roof, it ended up being very close in the cost when you considered the extra life span the green roof gave to the roofing membrane. Actually, the green roof was a bit more favorable,” -Nathalie Shanstrom, Kestrel (Seward, 55).

“Roof plantings on 100-year-old buildings in Berlin prove that they can last for the full life of a structure. Recent estimates show that increased costs are incurred initially with roof planting, but in the long run, it is more economical than other forms of construction,” (Kohler, 1444). Kohler’s information is derived by estimating that the construction cost of an extensively planted roof is about 2-4 times as much as a conventionally ballasted roof.

The maintenance costs are about 2.5 times as much for a planted roof. The savings is calculated by the financial advantage of adding more living area via a roof garden, a reduction in heating/cooling costs due to the insulation properties of the green roof, and the reduction in charges based on the amount of rainwater discharge in Germany.

AMENITY VALUE / INCREASED REAL ESTATE VALUE “We wanted something that would be green a long as possible during the year and also comfortable under bare foot,” – Heidi Blau, AIA from FXFowle (Seward, 55).

One could argue along the same line of thought as Fredrick Law Olmstead that a park setting in the city increases the public health of the occupants .

People want to be around nature, if not for any other reason than the air is cleaner and the temperature is lower.

Hell, an outside table in the shade is the most desired area in the summer time. Why shouldn’t everyone have access to this!

Image source: author 25

LIVING VERTICAL SYSTEMS

“As vegetated roofs, green vertical systems can be differentiated as extensive and intensive systems,” (Pérez, 4855).

Green façade at Peggy Notebaert Nature Center, Chicago Deciduous green screens will block intense radiation in the summer months, but will go dormant in the autumn and winter. This natural sun shade prevents the harsh UV radiation in the summer, and permits solar heat gain in the winter.

Green Facade Traditional green façades have the vegetation growing directly on the building’s façade, such as ivy growing on brick. The plants degrade the building’s façade material.

Double-skin green façade (green curtain) – The vegetation is supported by a separate curtain wall, vertically offset from the building’s exterior wall.

Living Walls “Made of panels and/or geotextile felts, sometimes pre-cultivated, which are fixed to vertical support or on the wall structure,” (Pérez, 4855).

Image source: author

“The measurements of the ambient temperature and humidity confirm that the green façade creates a microclimate in the intermediate space, characterized by lower temperature and higher humidity. This fact verifies that the green façade acts as a wind barrier and shows the effect of evapotranspiration of plants,” (Pérez, 4859).

PERSPECTIVE VIEW NEW CIRCULATION AND LIVING WALL 26

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Detail of Extensive Green Roof by Diller Scofidio + Renfro and FXFowle

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CONSTRUCTION & SPECIFICATION

“Assembly over the water proofing membrane is called the overburden,” (Snodgrass, 51).

Primary and secondary overflows are still required for roof drainage (Snodgrass, 51).

Vegetation: For extensive roofs, the plantings should bind the medium together via a shallow root system.

They should (Snodgrass, 65): • Be easily established via a shallow, lateral root system.

• Have low nutrient & maintenance requirements.

• Resist damage from disease & insects.

• Have low windborne seeds • Be lightweight at mature state Sedums – 400+ species and thousands of variations. “Be weary of specifying plants raised in a nursery medium, high organic content is not desirable for an extensive green roof,” (Snodgrass, 65).

“Sedums are succulents, whereby they store water in their leaves, leaving them highly drought resistant. They are small plants that grow across the ground rather upwards, offering good coverage and roof membrane protection,” (Castleton, 1583).

• Sedums - Sempervivum, Talinum Jovibarba, Delosperma. (Snodgrass, 65) • Cacti – Opuntia. (Snodgrass, 65) • Cuttings – Installed at 25-50 pounds per 1000 SF. • Plugs – Allows for more ambitious planting designs. Tray size and root depth may vary (Snodgrass, 75).

For 85% coverage (Snodgrass, 77): • 2 plugs per SF – 12-18 months • 3 plugs per SF – 9-12 months • 4 plugs per SF – 6-9 months Seeds – Snodgrass recommends over sowing barren areas with perennial or annual seeds that are rapidly germinating, drought-tolerant species.

• Seeds – Arctotis acaulis, Arctotis hirsute, Dorotheasthus Bellidiformis, Eschscholzia californica, Phacelia campanularia, Portulaca pilosa, Talinum calycinum (Snodgrass, 77).

Pregrown vegetated mats (Snodgrass, 79) They are best for quickly establishing a vegetated roof. Used for high wind applications, or when it’s late in the planting season.

Most expensive way to plant a roof.

Some engineers doubt the efficacy of these systems, they function as independent units rather than a cohesive system.

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“The daily [evapotranspiration] with a grass tray (2.34 mm) is larger than that with a Sedum tray (1.42 mm),” (Ouldboukhitine, 84).

At the ASLA headquarters, Sedum album, Sedum reflexum, Sedum spurium, and Sedum sexangulare performed better than Sedum lanceolatum and Sedum stenopetalatum. (ASLA Green Roof Monitoring Results).

Grasses performed very well, especially Eragrosits spectabilis (purple lovegrass)(ASLA Green Roof Monitoring Results).

Perennials that performed well included Allium ceruum (Nodding Onion), Coreposis verticillata (Thread Leaved Tick Seed), Ascelepia tuberose (Butterfly Milkweed). (ASLA Green Roof Monitoring Results). Black-eyed Susans struggled.

Growing Medium: The depth of the medium is a result of determining the plantings, typical rainfall, aridity of the region, and the designed rainwater performance (Snodgrass, 59).

Germany – 3”, Mid Atlantic & New England – 3-4” minimum, Southwest US (desert) 8-12” minimum plus top dressing (Snodgrass, 59).

Medium can be too deep. An 18 month study in Seattle found that water wasn’t able to drain / evaporate between rain events. 8” was too deep (Snodgrass, 60).

Organic Matter - Decomposes quickly Organic matter establishes plant life, 20% needed when planted in late summer or autumn, only 10% needed for spring plantings (Snodgrass, 60).

“Established green roofs (extensive) are usually only comprised of about 2-5% organic matter by weight,” (Snodgrass, 61).

Extensive Composed of mineral aggregates and only a small amount of organic material (Snodgrass, 52).

Good & consistent drainage and aeration, structure that enables it to hold water for uptake by plants, ability to make nutrients accessible to plant roots through cation exchange capacity, resistance to decomposition & compression, lightweight, physical & chemical stability (Snodgrass, 54).

Pumice from the Pacific Northwest volcanos is good to use. Expanded clay, shale or slate allows water and air to flow while maintaining structural integrity. Expanded aggregates require high amounts of embodied energy (kiln fired) to produce (Snodgrass, 55). Is there an opportunity 30

to recycle brick or other masonry products for use in the growing medium. Pulverized bricks could be a substitute for the production of new kiln fired materials (jp).

Root Permeable Filter Layers: “A separation fabric, a nonwoven geo-tech material that lets water pass through, but not soil or growing media,” (Seward, 52).

Drainage Layer: “The possibility of using recycled rubber from tires as a drainage layer in green roofs, substituting the porous stone materials currently used (such as expanded clay, expanded shale, pumice, and natural puzolana). This solution would reduce the consumption of these natural materials which also require large amounts of energy in its transformation process to obtain their properties,” (Pérez, 347) “A drain mat, involves plastic or fiber channels that direct water filtering thought the soil horizontally to drains in the roof.

The other, granular drainage, is made from single-sieve aggregate, basically little stones that are all the same size,” (Seward, 52).

Image source: werthmann, pg 115

“Planted roofs require falls of at least 1-2 percent to drainage outlets,” (Kohler, 1444).

Root Barrier & Protection Layer: Possible synthetic sheets to prevent membrane damage that could be caused by root infiltration.

The Target Center in Minneapolis used a recycled geo-tech material that functions to hold water.

(Seward, 53).

Water Proofing: Membrane suggestions for green roofs are listed by the NRCA. The FLL has guidelines for determining resistance of membranes to root damage (Snodgrass,90).

EFVM – Electric Field Vector Mapping is a leak-free detection system. Test for leaks in membrane before green roof is laid. Remains in place so that it can continue testing in the future.

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EFVM “uses a low-voltage current to create an electrical potential difference between the nonconductive waterproofing membrane and a conductive substrate,” (Seward, 52). Technicians can be highly accurate when locating leaks with this system.

“It is important to understand which material is used because while plants can’t consume PVC and TPO, asphalt-derivative products can become food for plants and bacteria. If asphalt is used, then an engineered-fabric root barrier must be added to prevent the roof’s living organisms from feeding off of (and in doing so, degrading) the roof’s waterproofing ,” (Seward, 51).

Roof Deck: Captured water is dead load. Minimum weight of extensive roof is a combined 13 psf. The standard extensive weight (between 3-4”) is 17-18 psf. Intensive roof systems weigh 35+ psf.

(Snodgrass, 88) “In most retrofit projects, such as [Chicago] city hall, we adapted the green roof system to the characteristics of the structure, varying the thickness of the growing medium bsed on available loading,” –David J. Yocca (Seward, 51) The green roof over Vancouver’s Convention Center doesn’t exceed 39.6 psf, (Seward, 53).

The green roof over the Target Center in Minneapolis doesn’t exceed 17.4 psf. Kestrel Design Group, (Seward, 53).

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SOME GROUPS & ORGANIZATIONS

Image source: author

Green Roofs for Healthy Cities North America (GRHC) – “Not-for-profit association working to promote the industry throughout North America.” http://www.greenroofs.org/ (06/03/2013) Fee: 160 USD Center for Environmental Innovation in Roofing (CEIR) – “Established by the National Roofing Contractors Association (NRCA), CEIR’s purpose is to establish a forum that will draw together the entire roofing industry into the common cause of promoting and increasing the knowledge base of environmentally friendly roof systems.” http://www.roofingcenter.org/ (06/03/2013) Fee: 160 USD International Green Roof Association (IGRA) – “is a global network, for the promotion and dissemination of information on Green Roof topics and Green Roof technology. Due to the status as multi-national, non-profit organisation, IGRA offers the platform and infrastructure for independent “pro Green Roof” lobby work with political decision makers and investors. IGRA members are national Green Roof organisations, Green Roof research institutes and Green Roof companies. IGRA also welcomes persons and Green Roof experts, who support the ecological Green Roof idea, to join the Green Roof network.” http://www.igra-world.com/about_us/index.php (06/03/2013) Fee: 80 EUR Chesapeake Bay Foundation (CBF) heavily invested in reducing stormwater runoff for the Chesapeake Bay watershed. Reduction in nitrogen is essential.

Rebroadcasting Sedums Image source: author 33

BIBLIOGRAPHY

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Rebroadcasting Sedums Image source: author

Castleton, H.F. and V. Stovin, S.B.M. Beck, J.B. Davison, Green roofs; building energy savings and the potential for retrofit, Energy and Buildings, Volume 42, Issue 10, October 2010, Pages 1582-1591, ISSN 0378-7788, http://dx.doi.org/10.1016/j. enbuild.2010.05.004. (http://www.sciencedirect.com/science/article/pii/S0378778810001453) Keywords: Green roof; Energy consumption; Structural capacity; Retrofit; Insulation Dvorak, Bruce, (2011) Comparative Analysis of Green Roof Guidelines and Standards In Europe and North America. Journal of Green Building: Spring 2011, Vol. 6, No. 2, pp. 170-191.

Claire Farrell, Xing Qi. Ang, John P. Rayner, Water-retention additives increase plant available water in green roof substrates, Ecological Engineering, Volume 52, March 2013, Pages 112-118, ISSN 0925-8574, http://dx.doi.org/10.1016/j. ecoleng.2012.12.098. (http://www.sciencedirect.com/science/article/pii/S0925857412004600) Keywords: Super absorbent polymer; Hydrophilic polymer; Polyacrylamide; Sanoplant; Soil conditioner; Substrate amendment Dunnett, Nigel, and Noël Kingsbury. Planting Green Roofs and Living Walls. Portland, Or.: Timber, 2004. Print.

Glass, Dr. Charles C. Green Roof Quality and Quantity Monitoring. Rep. Howard University & ETEC LLC, 26 July 2007. Web. 03 June 2013.

Hart, Sara. EcoArchitecture, the Work of Ken Yeang. UK: Wiley, 2011. Print.

Issa Jaffal, Salah-Eddine Ouldboukhitine, Rafik Belarbi, A comprehensive study of the impact of green roofs on building energy performance, Renewable Energy, Volume 43, July 2012, Pages 157-164, ISSN 0960-1481, http://dx.doi.org/10.1016/j. renene.2011.12.004. (http://www.sciencedirect.com/science/article/pii/S0960148111006604) Keywords: Green roof; Building energy efficiency; Cooling demand; Heating demand; Thermal comfort; Roof insulation Kohler, Manfred. “The Quantifiable Advantages of Planted Roofs,” DETAIL, Volume 51, Issue 12, 2011, Pages 1438-1446, ISSN 0011-9571.

Kosareo, Lisa, and Robert Ries, Comparative environmental life cycle assessment of green roofs, Building and Environment, Volume 42, Issue 7, July 2007, Pages 2606-2613, ISSN 0360-1323, http://dx.doi.org/10.1016/j.buildenv.2006.06.019. (http://www.sciencedirect.com/science/article/pii/S0360132306001648) Millard, Bill. “Designing the Building-Landscape Interface,” Architect Magazine, July, 2011, Pages 56-61.

Meyer, Molly, and Michael Repkin. “Beyond Extensive and Intensive: Defining the Comprehensive Green Roof.” OMNI Ecosystems. N.p., 25 Feb. 2013. Web. 03 June 2013.

Ouldboukhitine, Salah-Eddine and Rafik Belarbi, Issa Jaffal, Abdelkrim Trabelsi, Assessment of green roof thermal behavior: A coupled heat and mass transfer model, Building and Environment, Volume 46, Issue 12, December 2011, Pages 2624-2631, ISSN 0360-1323, http://dx.doi.org/10.1016/j.buildenv.2011.06.021. (http://www.sciencedirect.com/science/article/pii/S0360132311002010) Keywords: Green roofs; Water balance; Evapotranspiration; Foliage density; Experimental validation Pérez, Gabriel and Anna Vila, Lídia Rincón, Cristian Solé, Luisa F. Cabeza, Use of rubber crumbs as drainage layer in green roofs as potential energy improvement material, Applied Energy, Volume 97, September 2012, Pages 347-354, ISSN 0306-2619, http:// dx.doi.org/10.1016/j.apenergy.2011.11.051. (http://www.sciencedirect.com/science/article/pii/S0306261911007562) Keywords: Green building; Building envelope; Green roof; Passive system; Energy efficiency; Rubber crumbs Pérez, Gabriel and Lídia Rincón, Anna Vila, Josep M. González, Luisa F. Cabeza, Green vertical systems for buildings as passive systems for energy savings, Applied Energy, Volume 88, Issue 12, December 2011, Pages 4854-4859, ISSN 0306-2619, http:// dx.doi.org/10.1016/j.apenergy.2011.06.032. (http://www.sciencedirect.com/science/article/pii/S030626191100420X) Keywords: Green systems; Passive systems; Energy savings; Building Seward, Aaron. “The Grass Ceiling.” Architect Nov. 2011: 51-55. Print. 100 n11 Snodgrass, Edmund C., and Linda McIntyre. The Green Roof Manual: A Professional Guide to Design, Installation, and Maintenance. Portland: Timber, 2010. Print.

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PRECEDENT STUDY ASLA HEADQUARTERS - WASHINGTON, D.C. MICHAEL VAN VALKENBURGH ASSOCIATES

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Rooftop Social on ASLA Headquarters - 3 months after planting.

Image source: werthmann, pg 51

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Extensive Green Roof Thriving Below Grating - 3 months after planting.

Image source: werthmann, pg 53

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STAIRWELL

ELEV.

ROOF ACCESS MECHANICAL EQUIPMENT

RENOVATIONS TO BUILDING Image source: author

INTENSIVE SEMI-INTENSIVE EXTENSIVE

PLANTING ZONES Image source: author

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WOOD DECKING ALUMINUM GRATE

WALKING SURFACE Image source: author

PUBLIC PRIVATE / SERVICE

CIRCULATION ZONES Image source: author

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ARTIFICIAL HORIZON

ARTIFICIAL HORIZON CONTROLLED VIEWS Image source: author

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Image source: werthmann, pg 111 42

North Wave Succulents; Plant Descriptions by Richard Hindle (MVVA) and Marcus de la fleur (CDF)

image source: werthmann, pg 101

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North Wave Perennials; Plant Descriptions by Richard Hindle (MVVA) and Marcus de la fleur (CDF)

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image source: werthmann, pg 102

North Wave Perennials; Plant Descriptions by Richard Hindle (MVVA) and Marcus de la fleur (CDF)

image source: werthmann, pg 103

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Terrace Succulents; Plant Descriptions by Richard Hindle (MVVA) and Marcus de la fleur (CDF) 46

image source: werthmann, pg 106

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The green roof is an example of how a single architectural system has the possibility to affect many aspects of the built and natural environment. This investigation explores how green roofs can potentially minimize the ecological impact of the built environment, insulate a building and provide opportunities to introduce new types of program.

This pamphlet is broken into two parts, a research exercise and a design proposal. The research explores the concept, status of the industry and designs of existing green roof projects. The proposal is an application of the research to the The University of Tennessee’s College of Architecture + Design.

The College of Architecture + Design’s facility was designed to be a pedagogical vehicle for architecture students, and this proposed project will work to continue that conversation. This exercise helped to develop an awareness of the new technologies and materials that are available for green roof systems and how they can be best applied in the design and construction industry.