Case study green roofs

Case Study

Joseph Glesta #663728

#156: South Geology Roof Green Roof Design

This paper will review the information pertaining to the theorized creation

and design of a green roof to be placed on the old Geology south building #156.

The creation of this project will be based largely upon information ascertained from previous experiments gathered throughout educational sessions during the course: Green roof and Green walls. The intention of this project is to provide an overall analysis of the details required to create a functional, feasible and holistically designed green roof. The roof will be designed to help manage storm water, extend the life of the roof system, add an aesthetically pleasing landscape to a barren roof, help reduce the urban heat island effect and reduce the energy demands of the building by providing better insulation. An analysis of the current site will be demonstrated in order to examine the feasibility of such a project.

Suitability of the current Roof: The roof of building 156 is a suitable location for a green roof due to its sun exposure, its weight loading capacity and the roof’s need for replacement and/or repairs. The necessity for a new roof system is due to the current roof’s poor condition, which requires replacement due to water ponding and irregular roof slope, which inhibits proper drainage (Fig.1).

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Green Roofs and Walls

Water Tank and Pump

Areas of ponding caused by lack of proper drainage and the slope of the roof.

Sloping and drooping of certain areas indicate degradation of the roofs original design and function.

Figure 1: Picture of the roof site, showing areas of ponding, and the current condition that the roof is in.

The roof's waterproofing layer needs replacement and the slope of the roof require readjustment due to inadequate drainage

Current Roof Characteristics The approximate measurements of this roof are 12 meters wide by 43 meters long (Fig 2.) (Google Earth 2014). The roof also has six drainage points that are not entirely functional. This is because the slope of the roof, does not allow the water to naturally progress towards these drainage points and facilitate appropriate runoff during storm events. The length and width of the roof are of adequate size to create a fully functional space for both plant life and pedestrian use. This is because the roof has support columns throughout its mid section, which are able to withstand a higher load bearing capacity, (400kg/m2) allowing for human use and larger capacity for footpath infrastructure, seating/recreation space and vegetation. The roof has a load bearing capacity of 300kg/m2 for the majority of its area, and has a higher load bearing capacity within the area of its support columns as aforementioned (Fig. 3).

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Drainage points

Figure 2: Illustrated aerial perspective of roof site. This is a digital recreation of the roof on south geology building 156. The length of the roof is 43 meters long and the width is 12 meters wide. This representation shows the available space for the potential green roof. The grey boxes represent space that cannot be used and/or are allocated for different purposes.

North -­‐-­‐>

Key

Area that cannot be altered Load bearing capacity 400kg/m2

Load bearing capacity 300 kg/m2

Area of counter levering weight load distribution

Figure 3: This illustration depicts the Absolute load bearing capacity zones on the roof of the old geology south building 156. Different colours represent varying load bearing ability. The orange circles specifically represent the support columns for the roof, where there is a higher load bearing ability.

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Site Analysis: Old Geology South- Building 156 Table 1: This table identifies the key components of a site analysis, in order to asses the feasibility of a green roof (adapted from the Melbourne Growing Green Guide). The data provided by this site analysis comes from: on site inspection, engineering specifications and statistics provided by the Australian bureau of statistics predicted forecasts.

Properties

Results The seasons fluctuate in temperature for Melbourne leading to variability in daily highs and lows. This will be taken into account regarding irrigation requirements and plant type (Australian Bureau of Statistics 2011).

Seasonal Consideration and Climate

Rainfall

The green roof will require irrigation due to the lower amount of rainfall during the hotter months, caused by higher evapotranspiration rates (Australian Bureau of Statistics 2011).

Local environment Weight Load Capacity Drainage Irrigation

Existing

structure and size Access

Wind

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A nearby ash tree poses a threat, as its seeds may germinate the green roof. Pests and animals, such as possums may use the tree to climb onto the roof, which may cause vegetation damage. Therefore a removal of the higher branches that overhang the roof would be advised.

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As can be seen in figure 3, the weight loading capacity varies from 300kg/m – 400kg/m This can be further augmented to support higher weight loads, through counter levering beams across the span of the support columns and the sides.

There are 6 drainage points located throughout the roof as can be seen in Figure. 2. These drainage points may need to be expanded and or altered to work better with a future design.

The roof has a water pump and water tank reserve (1600L) on it, which is currently in use by the building.

This pump could potentially be used to help, flush water through the irrigation system when needed. A water storage tank is also recommended to naturally obtain water, and can be placed on a high load bearing area such as the stairwell.

The current roof is 12 m x 43 m. However, only a portion of this roof will be used to facilitate a green roof, as the rest of the roof should be partitioned off so that pedestrians cannot access it, due to safety concerns, maintenance of existing infrastructure and aesthetics.

There will be access to a crane in the upcoming months due to HVAC installation. This would mean that while the crane is being used to transport HVAC materials on the roof, it could also be used to bring up supplies for a green roof, which would reduce cost by limiting the amount of times a crane must be used to haul materials.

Because the roof is 5 stories up, the wind is much more volatile due to exposure; windshields are advisable in order to ensure adequate safety and protection to vegetation and pedestrians.

Substrate selection The fundamental aspects of a green roof are important to perfect in order to create an optimal/functional roof and living environment. The foremost important aspect of a green roof lies within its substrate (Fig 4.), which acts as a growing bed for plants, insulation for the roof and as a rainfall/storm water management system via its ability to absorb water and retain it for plant use.

Figure 4: Illustration of substrate, with labels of each layer. This is an example of what will be used on the green roof of the old geology south building, 156.

The best-suited substrate for this green roof will be Scoria with an

additional mixture of Bio-Char at 40%. The reason for using scoria is due to its low bulk density weight, which is very important especially in lower weight loading roofs such as building 156 (Table. 2). It is also being used because scoria’s water holding capacity (WHC) is 40%, which is higher then other substrate mixtures and allows for a greater variety of plant life (Farrell et al.

2013).

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Green Roofs and Walls

Properties of Scoria mixed w/ Bio Char Table 2: This table displays the properties of Scoria mixed with Bio Char at 40%. These results conclude that scoria is able to retain much more water when mixed with Bio char and therefore creates a higher

Properties Water Holding Capacity (WHC) Wilting Point (Soil Moisture content where water can no longer be attained) Air Filled Porosity (AFP) Plant Available Water (PAW) Saturated Bulk Density (BDS) Dry Bulk Density (BDD)

Results 79.11% (.37) Occurs at 20% of WHC 11.38 (.82) 8.4 % of WHC (% of WHC at Permanent wilting point = 1.5 MPa 1.2 (0.02) .061 (0.006)

PAW, ensuring better water retention for both storm water management and plant use

The reason for mixing bio-char with scoria is to increase plant available

water (PAW). This means the amount of available water that can be used by a plant through its root system absorbing the moisture, as opposed to the WHC, which is the substrates capacity to hold moisture. This is important because even though scoria may have a high WHC, it does not mean that all of that water is available to the plant to use. Therefore, an addition to the substrate is required to ensure adequate PAW. That is why the use of Bio-Char, when mixed at 40% with scoria, is optimal, and increases the substrates overall WHC, by ensuring that the water is kept within the pores of the organic material, making it accessible for plant use (Beck et al. 201, Farrell et al. 20131). This additional mixture of BioChar allows the substrate to retain more water, which in turns reduces storm water runoff and increases PAW. This mixture of Bio-Char and Scoria is necessary for this green roof because it is able to absorb and retain water better, which is very important in environments prone to drought and high temperatures such as Melbourne. This substrate mixture will be installed on the green roof at different depths according to plant needs, however the maximum depth will be 190mm as weight restriction (300 - 400kg/m2), maintenance load capacity (100kg/m2) and plant type dictate the feasible weight load allowed on the roof. This weight restriction and substrate

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depth calculation is a result of estimates based upon FLL guidelines (2008) that indicate the required substrate depth for each plant type. Furthermore, additional calculations were used to ensure the roof has the ability to hold live weights (Substrate with plants). The following table (Table 3.) shows the substrate depth allowed upon building 156, which has varied weight-loading capacities ranging from 300Kg/m2 to 400Kg/m2.

Substrate Depth for the roof of Building 156

Table 3: This Table shows the minimum and maximum amount of substrate depth determined by weight loading ability on building 156. These numbers were attained according to FLL guidelines 2008 which dictate various weight loads and minimum standards for a roof to meet in order to facilitate a live load. * Weight Loading kg/m2 = (saturated Bulk Density g/cm3) x substrate volume (cm3/m2)/1000. ‘ The resulting weight load that was leftover from these calculations is what is available for substrate.

Green Roof Vegetation Type

Dead Load Capacity Kg/m2 of roof

Weight Load of roof after deducting Maintenance load, People and plants 135.6 Kg/m2

*Load bearing capacity (300kg/m2) 110mm >

*Load bearing capacity (400kg/m2) < 196mm

125.4-­‐ 135.6 Kg/m2

104mm >

< 187mm

115.2 Kg/m2

98 mm >

< 179mm

Low Herbaceous Succulents and grasses Low Perennials and Shrubs up to 1.5 meters Shrubs up to 1.5 – 3 meters

(This is the weight that is used for substrate)

Resulting Substrate depth using Scoria/Bio Char mix (Millimeters)

Plant Selection Knowing the limitation of substrate depth allows a greater focus on plant selection, and narrows down the various plants that could potentially be used on the roof. The constraints that became evident after assessing substrate depth were limiting to overall plant selection. This was because certain plants require a minimum amount of substrate in order to survive, which inhibited plant selection by limiting the type of plants that could be used (especially plants larger then grasses). Plants were then chosen based on their ability to survive in substrate

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Green Roofs and Walls

less then 190mm deep and were further refined based on criteria that would create a holistic design that combined: drought resistance, aesthetic use, biodiversity, nativity to local environment, and if these plants had been used in Melbourne green roofs already. Based upon these criteria, plants were then selected (Table 4.) and analyzed according to their characteristics and applicable traits for the roof.

Selected Plants Table 4: This table lists the plants, their characteristics and reason for potentially using them. The majority of them are to be drought tolerant as the green roof will be sloped in order to drain excess water, and a two plant types will be used for active storm water management. information sourced from the Burnley Plant Guide and Yarraranges.com.au and site observation of green roofs in Melbourne.

Plant Lepidosperma gladiatum (Sword Rush) #1 on planting guide

Dianella admixta (Black Anther Flax Lilly) #2 on planting guide

Plant Characteristics -

Reason for Choice

Can withstand Full sun exposure and temperature fluctuations Drought tolerance Native

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Can withstand Full sun exposure and temperature fluctuations Drought tolerance Native

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Lomandra longifolia (Basket Grass) #3 on planting guide

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Can withstand Full sun exposure and temperature fluctuations Native Water retention

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Stypandra glauca (Nodding Blue Lilly) #4 on planting guide

Aloe Aborescens (Candelabra Aloe) #5 on planting guide

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Can withstand Full sun exposure and temperature fluctuations Drought tolerance Native to region

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Can withstand Full sun exposure and temperature fluctuations Drought tolerance

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Aesthetic Drought tolerant Within Substrate parameters Low maintenance Used within Melbourne Green roofs already.

Aesthetic Drought tolerant Within Substrate parameters Attracts Birds (creating a habitat) Low maintenance Used within Melbourne Green roofs already.

Aesthetic Storm water management Within Substrate parameters Low maintenance Used within Melbourne Green roofs already.

Aesthetic Drought tolerant Within Substrate parameters Low maintenance Used within Melbourne Green roofs already.

Aesthetic Drought tolerant Within Substrate parameters

Anigozanthos cultivars (Kangaroo Paw) #6 on planting guide

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Native/exotic

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Low maintenance Used within Melbourne Green roofs already.

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Can withstand Full sun exposure and temperature fluctuations Drought tolerance Native to region

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Aesthetic Drought tolerant Within Substrate parameters Attracts Birds (creating a habitat) Low maintenance Used within Melbourne Green roofs already.

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Bulbine bulbosa (Bulbine lilly) #7 on planting guide

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Can withstand Full sun exposure and temperature fluctuations Water retaining Native to region

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Agave multifilifera (Shaggy head agave) #8 on planting guide

Austrostipa scabra (Spear-grass) #9 on planting guide

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Can withstand Full sun exposure and temperature fluctuations Drought tolerance Native/Exotic

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Can withstand Full sun exposure and temperature fluctuations Drought tolerance Native

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Aesthetic Storm water management Within Substrate parameters Low maintenance Ground cover Used within Melbourne Green roofs already.

Aesthetic Drought tolerant Within Substrate parameters Low maintenance Used within Melbourne Green roofs already.

Aesthetic Drought tolerant Within Substrate parameters Low maintenance Used within Melbourne Green roofs already.

After this process was completed the plants were then allocated within a design plan to conceptualize aesthetics, storm water management and diversity in seasonal flowering (fig. 5). The design then dictated that the roof will have to have different sloped plant beds to accommodate plant water retention requirements and drainage needs. However, the roof will require some irrigation in order to ensure that plant life remains lush all year round, especially in the dryer, hotter season of summer where evapotranspiration rates increase exponentially. In order to facilitate this irrigation use, a large water tank is suggested to be placed on top of a load bearing structure such as the stairwell roof and use a gravity pump to help irrigate the landscape, thus reducing energy and water demands. This can be used in conjunction with the pre existing water

Â

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pump on the roof to help maintain regular irrigation schedules when needed. The irrigation of plants will commence during evenings through drip lines, as this is the best time for water absorption for plants and requires very little maintenance (Farrell et al. 2014: Lectures).

Planter #8 Load bearing planter

Plant Bed #1,2,9 Drought tolerant

bed

Plant Bed # 3,7 Storm water retention bed

Plant Bed # 6,4 Drought tolerant bed

Planter #8 Load bearing planter

Roof coverage #5 Ornamental drought tolerant ground cover

North

Figure 5: This rendering depicts an aerial representation of the proposed green roof. Various planting beds are used for variations in climate. Storm water retaining beds cluster the borders of the drought tolerant beds in order to absorb more moisture, which is provided by the slope of each b ed creating increased runoff. Load bearing planters are placed in position around support columns which provide better load bearing capacity for large plants that will act as focal points within the green roof. The overall coverage of the roof is covered in ornamental succulents, which seem to do very well in Melbourne’s climate and in green roofs throughout the city.

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Storm Water Management

As can be seen in Figure 5, the design for the green roof ensures that water is

captured within the substrate and is diverted to the water retaining grow beds. The reason for this is the slope of the various plant beds. The proposed green roof will be bisected down the middle along a horizontal plane spanning the length of the roof along the east/west axis (Figure 6.). This bisection will be the point from where the footpath subdivides the beds and acts as the highest point on the green roof in built upon the support columns for maximum load bearing capacity.

EAST 1.4 meters: Footpath 1.1 meters: Drought tolerant bed .6 meters: Ornamental .3 meters: Water retaining bed

WEST Cross section of roof slope

Figure 6: These illustrations depict the various elevations that can be used to manage storm water runoff by creating areas of higher flow and reduced flow for higher water retention in different growing beds. The Water retaining bed will have a slightly inversed slope to capture more water, however an additional underlying drainage point will be placed under the water retaining bed so there will not be over saturation. This system will ensure seasonal fluctuations will not interfere with aesthetics, and also ensure that the roof will require lower maintenance and have higher water retention during storm events.

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Green Roofs and Walls

The beds falling to either side of the footpath will gradually decline pitching

towards the drainage points. Sloping the plant beds in different angles to absorb the most amount of water has been shown to be an effective method in preventing storm water runoff (Van Woert et al. 2005). Putting this fact into consideration, the bottom of these sloped beds will fan out into the water retaining beds to absorb the runoff created by the sloped beds. These water-­‐retaining beds will act as water-­‐capturing eaves to help mitigate storm water runoff by having plants that will absorb high amounts of water. A common occurrence with sloped planted beds is that they tend to slump, meaning the substrate slides towards the base of the bed. In order to prevent slumping from the various slopes, wire mesh will be spread around the substrate and plants to suppress movement (Van Woert et al. 2005).

The proposed green roof will also host drought tolerant plants to help

maintain greenery throughout dry spells. These plants will be along a much steeper incline for faster runoff to ensure that they do not become over saturated. This means that irrigation will have to be used during the hotter/dryer months, but can be directly irrigated into the beds that require more irrigation, rather then blanketing the entire roof. This will reduce water demand by focusing irrigation directly into the storm water retaining beds, allowing the drought tolerant plants to survive, without additional irrigation needs. As much as the substrate is important in dictating the degree to which water is absorbed, it is the plants that do almost all of the work. This is because the plants are conduits of water uptake and therefore act as the sources of water retention (Mentens et al. 2006).

Quantifying Storm Water Management Design

Calculations based upon a framework of substrate depth/type, plant type

and rainfall have helped estimate the total days that irrigation would be needed in order to have a fully functioning system. Most of the plant types proposed have similar composition to dianella and therefore can be assessed along similar parameters. Using a spreadsheet provided by Professor Tim Fletcher (2014), an estimation of the water retention of the plants (dianella), days required to irrigate and number of days with potential runoff was concluded, which led to a synthesis of 12

the potential storm water management of the roof. The evidence provided that on average the dianella type plants, would require irrigation for around 50% of the year (estimates around 191-­‐209 days out of 365), while their water retention would be helpful in reducing runoff an estimate of 77-­‐80 days of the year.

Unfortunately there is no specific data for the plants chosen for their water retaining abilities on green roofs in Melbourne. However, because irrigation would be channeled through drought tolerant beds, runoff/seepage would facilitate indirect irrigation, allowing these plants to have adequate water during the days that irrigation would be needed. This would mean that water retention and storm water management would be plausible for a roof such as this and has the potential to capture 54-­‐75% more rain water then a conventional roof (Lou 2003; Mentens et al.

2006).

However, because a synthesis of each plant cannot be conducted due to the

specificity of each plants characteristics/traits, these numbers may be altered. This is because the majority of the grasses are much more drought tolerant then dianella and therefore have lower water retaining qualities. This is in contrast to other plants within the proposed plant guide that have higher water retaining characteristics, which creates a balance between seasonal fluctuations more readily then a singular species. Moreover, additional vegetation to a roof will always provide much more storm water management then a bare roof, and the combination of substrate depths greater then 100mm and plants that help absorb water will only increase the effectiveness of this system (Lou 2003; Van Woert et al. 2005; Beck et al. 2011).

Another factor, which dictates water retention, is the placement of the plant beds and the types of plants in the bed. As can be seen in the planting guide and elevation plans (figures 5 & 6), a series of beds with different slope and water retaining properties encourage retention of water and require less of it. This method would therefore alter the properties of water retention due to the plants capture and saturation rate.

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Additional Benefits of the Proposed Green Roof

Academic Literature and case studies from around the world have been able to quantify the positive effects of green roofs within cities. Examples of how green roofs are able to provide these positive benefits have been seen especially within the environmental sector. This is because cities often displace local flora and fauna, which disrupts natural habitats. Therefore, the reintegration of natural plant species through green roofs has helped provide habitats for local flora and fauna that may otherwise have been displaced (Torrance et al. 2010; Jim 2004).

Furthermore, this also helps create bio diversity by increasing the array of plants that may have been reduced and or destroyed from the area (Torrance et al.

2010). The green roof proposed for building 156, adheres to these principles by supplying local native plants that attract a variety of local fauna to them.

Other examples of the beneficial implications of green roofs on the environment come from green roofs ability to reduce UHI (Urban Heat Island Effect), improve storm water retention and increase green space by developing otherwise unusable space such as black pitch roofs (Kazmierczak & Carter 2010; Ansl & Appl 2012; Jim 2004). As can be seen from the proposed design, of the green roof, the replacement of the black pitch roof allows for natural reflection of heat and sun, which cools the area as opposed to absorbing the heat. Additionally, this roof has been designed to manage storm water by absorbing water through substrate and plant uptake. The green roof also integrates design features that enable year round productivity in the plants, which means that the roof would continue to support life and would extend the life of the roof by becoming a functional insulated surface. These positive side effects of green roofs are just some of the factors that support the necessity to install a green roof on an underutilized roof such as building 156. The potential to create a habitat on a dormant roof will only further spread awareness of the positive implications of green roofs in urban environments.

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Rendering of proposed Green roof: At site location

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Green Roofs and Walls

References Ansel, W. Appl, R. 2012, “Green Roof Policies - an international review of current practices and future trends”. International Green Roof Association (IGRA). Nürtingen Beck D.A., Johnson G.R. Spolek G.A. 2011 “Amending greenroof soil with biochar to affect runoff water quantity and quality.” Environmental Pollution,159, 2111-2118 Farrell C., Ang X.Q. & Rayner J.P. 2013 “Water-retention additives increase plant available water in green roof substrates”. Ecological Engineering, 52,112 - 118.

Jim, C. Y. 2004, “Green-space preservation and allocation for sustainable greening of compact cities.” Cities, 2 (4) pp. 311-320.

Kazmierczak, A. Carter, J. 2010, “Adaptation to climate change using green and blue infrastructure.” A database of case studies.

Liu, K. 2003. Engineering performance of rooftop gardens through field evaluation.

National Research Council Canada Institute for Research in Construction.

Ottawa, Ontario Mentens, J., Raes, D. and Hermy, M. 2006 “Green roofs as a tool for solving the rainwater runoff problem in the urbanized 21st century?”

Landscape and Urban Planning 77:217-226 Torrance, S. Bass, B. Maclvor, S. Mcglade, T. 2013, “Design Guidelines for Biodiverse Green Roofs”. Zoning bylaw and Environmental Planning.

Toronto City Planning Division. Toronto Van Woert, D. Nicholaus D. Rowe, B. Andresen, J. Clayton L. Rugh, R. Fernandez, T. Xiao, L. 2005 “Green Roof Stormwater Retention: Effects of Roof Surface, Slope, and Media Depth” Journal of Environmental Quality 34:1036-1044.

Websites Australian Bureau of Statistics: http://www.abs.gov.au Date Accessed, July 25th, 2014 Burnley Plant Guide: https://bpg.unimelb.edu.au Date Accessed, July 27th, 2014 Indigenous Flora and Fauna Association: http://www.iffa.org.au Date Accessed, July 22nd, 2014 Yarra Ranges: http://fe.yarraranges.vic.gov.au Date Accessed, July 27th, 2014 Google Earth: Google Earth downloadable extension Date accessed, july 25th, 2014

Lecturers & Lectures Dr. Claire Farrell-

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Green roof and Green wall lecture series, 2014 Dr. Tim FletcherHydrology and plant water retention, 2014 Mr. John RaynerGreen roof and Green wall lecture series, 2014

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