Green Roof Trials Monitoring Report · GREEN ROOF TRIALS MONITORING REPORT CONTENTS Executive...

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1 Green Roof Trials Monitoring Report Prepared by Fifth Creek Studio For SA Government’s Building Innovation Fund and Aspen Development Fund No.1 2012

Transcript of Green Roof Trials Monitoring Report · GREEN ROOF TRIALS MONITORING REPORT CONTENTS Executive...

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Green Roof Trials

Monitoring Report

Prepared by

Fifth Creek Studio For SA Government’s Building Innovation Fund

and Aspen Development Fund No.1

2012

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GREEN ROOF TRIALS MONITORING REPORT

CONTENTS Executive summary 4 Background Building Innovation Fund 6 Site Location, orientation, overshadowing 8 Design Design criteria and development 9

Construction issues Installation 13 Monitoring methodology Green roof heat flow 15 Green roof system layers Understanding thermal behaviour in substrate Roof surface temperature Air temperature above green roof Role of water in the system Developing an R-Value – is it possible? Grating shading impact Plant characteristics Water quality Water use - irrigation Findings NABERS: Energy reduction and 28

greenhouse gas emissions Providing habitat Park Island and UHI effect

Estimated Capital Costs 29 Conclusions 30

Acknowledgements 31 Appendix – refer to separate documents

1. Determining and understanding thermal characteristics of green roofs in the City of Adelaide by Prof Roger Clay, et al, University of Adelaide

2. ANZ House Green roof trials stormwater quality, University of

South Australia 3. Report on Building Energy Impacts of “Living Wall” and “Green

Roof” Project prepared by behive Built Environment Sustainability

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Executive summary

Green roofs have been shown to benefit buildings through thermal insulation in many climates, but seeking to understand this process in Adelaide’s demanding hot, dry climate has created some interesting results. For instance this research has shown that the temperature above the green roofs does not fall in comparison to the control roof, which appears to be at odds with the industry’s general acceptance of a reduction in air temperature above a green roof. Our research is based on real life experience on a high rise building, with this finding perhaps indicating that the green roof’s evapotranspiration is not sufficient, and/or the height of this particular location experiences constant wind movement creating a flux that mixes the air temperatures. We have shown that the insulation value of a 125-300 mm thick profile is sufficient to reduce summer heat flow in Adelaide’s climate. The deeper the profile the larger the insulation value and the longer the time delay for peak temperatures. This is based on a dry substrate condition. The introduction of a 125 mm profile with an aluminium grating with a 150 mm air gap shows considerable insulation improvement over the extensive green roof of 125 mm profile. This profile provides the opportunity for retrofitting because of its light weight and good insulation values. When water is introduced into the green roof systems the insulation values reduce as temperatures within the profile layers rise, because water is a good thermal conductor. This is evident in the drainage layer immediately above the roof slab as temperatures rise in this layer. There is a strong argument now in a hot, dry climate to redesign the green roof profile to remove water from the profile during the hottest period of the day. The reverse could apply during the cool temperatures at night

when the profile is watered. Heat from the inside of the building can escape through infra-red radiation through the roof and green roof while the green roof profile is moist at night. The insulation value such as R-Value is difficult to calculate with the existing data, but a temperature reduction can be used for the various green roof profiles in Adelaide: 300 mm profile gives a 41% reduction in temperature in oC, 125 mm + grating gives 20.5% reduction, and 125 mm profile gives an 8% reduction. These figures can be used as a general guide or toolkit for Adelaide’s conditions. This design tool could be used for a Mediterranean climate and will be useful for pre-planning a building’s energy budget. The GreenStar rating in Australia for green roofs requires no irrigation after a three month installation and establishment stage. This unintentionally eliminates the opportunity to remove heat from the building using the moisture in the green roof. Given this current research this GreenStar rating requirement should be changed for a hot, dry climate to allow irrigation at controlled times such as at night time. This would reduce energy and GHG from the building. In stormwater quality the performance of the 125 mm extensive green roof was better than the 300 mm intensive system in terms of pollutant removal. This may be related to the reduced volume of soil that can leach pollutants. In terms of potential recycling of outflow water from green roofs, it can be reused for urban landscape irrigation and for non-potable purposes such as toilet flushing in buildings. Although not part of the project brief it was observed that a white aphid outbreak occurred 12 months after installation, and these insects were being farmed by ants. This suggests an airborne colonisation. Similarly, moths, bees and birds have used the green roof plots as part of their habitat.

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The building energy impact resulting from the 125 mm profile + grating in summer reduces the heat transfer through the roof by 4.2 W/m2 for a NABERS 5 Star rated commercial building using ‘chilled beam’ technology. This project has shown that green roof design needs to be carefully considered in a hot, dry climate. The use of a grating to shade the substrate and vegetation shows great potential, and especially when constructed around plant equipment it provides a light weight trafficable surface in addition to the environmental and energy saving benefits of the green roof system. Graeme Hopkins and Christine Goodwin Fifth Creek Studio August 2012

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Background Building Innovation Fund The South Australian Government’s Building Innovation Fund (BIF) aims to demonstrate innovative ways to reduce the carbon footprint of existing commercial buildings. The fund offers grants to owners of office buildings and some hotels and shopping centres for initiatives that demonstrate new and leading edge approaches to reducing a building's energy use and greenhouse gas emissions. The fund supports the commercial property sector agreement between the South Australian Government and the Property Council of Australia (South Australian Division) made under South Australia's climate change legislation.

On 30 July 2009 Aspen Development Fund No. 1 Ltd successfully applied for grants from the Building Innovation Fund to contribute to the cost of undertaking three projects. This report describes one of the approved projects from the grants program, the Capital works stream for implementing leading edge approaches in retrofitting commercial buildings.

Initial installation and monitoring of several green roof systems to the Darling Building (subsequently approved to be located instead on ANZ House) and, subject to consent by the Minister, relocation to another building or buildings owned by the Aspen Group within the Adelaide CBD.

Extracts from the BIF application for the green roof project provide background to the focus and anticipated benefits of this project.

Project summary (BIF application) Several green roof systems will be installed and monitored for environmental benefits including insulation, stormwater retention, cost effectiveness and visual amenity. They will be compared for their performance in this demanding climate to develop a bank of knowledge of the various systems' benefits. This will become a benchmark toolkit for green roofs in Adelaide. Project innovation and demonstration potential (BIF application) These green roof prototypes are to be located on an existing 4 storey building roof (now on the 22nd level roof of ANZ House) which is a unique testing situation, as the conditions will be simulated for the high rise nature of commercial buildings. The higher you go the more extreme the weather conditions are for the plant material on a green roof. Testing green roof systems on the ground, which has occurred in other states, does not give accurate results for high rise situations. This project will become a benchmark for Adelaide CBD conditions. The location of the prototypes is in the City Central Tower precinct, which provides a unique opportunity to assess how the green roofs respond to the changing wind patterns and velocities around a building complex. These green roof prototypes will be a strong visual demonstration of various systems to potential building owners, developers, architects and engineers. The demonstration quality of these roofs will be such that people will be able to observe their performance or to view them from surrounding buildings. The performance results will become the basis of green roof technology for Adelaide. This performance information will be quickly disseminated through the relevant professional bodies as there is a gap in the knowledge and best practice for this technology in Australia.

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The project’s greenhouse gas emissions abatement potential (BIF application) These green roof prototypes will be monitored with thermal sensoring and relative humidy readings. This information will be vital in assessing the impact on building performance as well as its contribution towards the heat island effect. This monitoring will be linked to another project that is currently being undertaken jointly by Flinders University and the Department of Planning and Local Government, where the City's heat island effect is being measured from satellite imagery through to ground monitoring in the Adelaide CBD.

This green roof prototype project is an ideal case study for the heat island project. The results of the larger heat island study can then be related to a specific building performance. When the findings of the two projects are combined this will provide a powerful tool for green building design. This will not only be a City planning tool but will enable quantative assessment for retrofitting existing buildings with green roofs and the potential climate change mitigation within the City.

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Site

Location The site selected for the green roof trials is located on the ANZ House rooftop at 10 Waymouth Street, Adelaide. The site is an area set down on the concrete roof between the fire water tank plinth and the building maintenance unit (BMU) plinth around the edge of the building. The concrete roof surface is covered with a waterproof asphalt membrane and the area is divided into three drainage basins with sumps to the stormwater outlets. Two basins contain the 4 test plots and the third basin is the control roof surface.

ANZ rooftop site before green roof installation

Western shade from screens and tank

Orientation This site is located on the eastern side of the building and is open to the northern aspect. This orientation allows for full sun in the morning and to midday. After midday there is some shading effect, especially in winter. The site receives a large solar exposure and is sheltered from the west winds, thus creating a hot micro climate. Overshadowing

The fire water tank and the two vertical screens on the western edge of the site provide shading and shelter from afternoon sun and drying west winds. This overshading does not reduce the extreme climate of the roof but provides a realistic example of complex micro climates that are encountered on roofs of multi-storey buildings.

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Design

Design criteria and development Four green roof systems were installed and monitored for environmental benefits including insulation, stormwater quality, water use, cost effectivenes, vegetation and visual amenity. They were compared for their performance in this demanding climate to develop a bank of knowledge of the various systems' benefits. Two proprietary systems that are the most commonly used in Adelaide and Australia were selected to represent two different substrate thicknesses. It is anticipated that the results of these trials will become a benchmark toolkit for green roofs in Adelaide. The design criteria or brief was for four green roof prototypes to be installed on the 22nd level roof of ANZ House, which could either be removed after the trial period, or stay as part of a long term experience if the building owners were agreeable. The four plots were to be divided into two different substrate depths of 300 mm and 150 mm. The 150 mm plots were to be further divided into halves, with the second half plots to be covered with an open mesh or grating above the plants. The reasoning behind this selection of substrate depths was that from experience we knew that 300 mm could be successful in the Adelaide climate, but there was little evidence that a 150 mm substrate would work successfully in this extreme climate and location. Two proprietary green roof systems commercially available in Australia were used and identified as System A and System B. The intention was not to compare these commercial systems, but rather to compare the profile depths. The intensive profile depth of 300 mm and the extensive profile depth of 150 mm were identified by the first letter of each type, giving the following identification to the plots.

Summary of green roof plots Ai – System A intensive profile Bi – System B intensive profile Ae – System A extensive profile Be – System B extensive profile Plus Ae and Be subdivided for mesh/grating C – control roof The concept for the grating came from two sources. The first was a National Parks and Wildlife Service project at Lincoln National Park in 2004 where Fifth Creek Studio designed a boardwalk constructed from metal grating over sand dunes. It was observed that the grating provided a sheltered micro climate under the walkway for germination of spinifex grass, whereas the grass regeneration on the open dune was less intense.

Grating used on sand dunes to assist vegetation growth with pedestrian access The second example drawn upon was the green roof on the American Society of Landscape Architects office in Washington (2005) which uses grating to provide a trafficable surface over the plants. It was again observed that a favourable micro climate benefited the plants’ growth. Using these observations, the idea of creating a sheltered micro climate between the grating and the vegetation on the green roof seemed like a sensible approach in such an extreme climate as Adelaide. If this approach is successful then it opens up a new market for lightweight green roofs for new and

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retrofitted buildings, but with the thermal and environmental benefits of a thicker roof. The design of the green roof plots had to take into consideration restrictions on access to the site, such as the size of the goods lift for delivery of components, and strict weight bearing and load distribution requirements once on the rooftop. The design saturated weight per m2 for the three types of green roofs is as follows: 300 mm profile (including soil, hydrocell, plants, mulch) 290 kg/m2 125 mm plus grating (soil, hydrocell, plants, mulch, grating) 124 kg/m2 125 mm profile (soil, hydrocell, plants, mulch) 117 kg/m2

As the green roof plots needed to be self-contained and eventually removable, aluminium trays were designed that could be bolted together onsite once the components had been carried up onto the rooftop. Aluminium was selected for its rigidity, relatively light weight, ability to withstand extreme environmental conditions and resistance to corrosion or rust.

Assembling aluminium trays and grating on site

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Construction issues

The green roof trays and all the materials for the trials needed to be transported from the basement carpark by goods lift and then carried up the final floor via the stair well, and through the plant room to the rooftop site. Installation was conducted at weekends to minimise any impact on the occupants of the building, and for easier use of the basement carpark for delivery, unloading and organisation of materials.

Basement delivery and lift access for materials

View from ANZ House rooftop

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Plant selection

Each green roof plot was planted with the same number, species and layout of Australian native plants. The tube stock plants were set out at 600 mm centres in four rows of each species. There were two ground cover species: Carpobrotus rossii (native pig-face) and Myoporum parvifolium (creeping boobialla); and two grasses: Dianella ‘Tasred’ (flax lily) and Lomandra ‘Nyalla’ (mat rush).

Left: Carpobrotus rossii Right: Myoporum parvifolium

Left: Dianella ‘Tasred’ Right: Lomandra ‘Nyalla’

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Installation

The green roof installations consisted of four plots, with two of these further subdivided into another two sections, giving a total of six plots. Two plots were intensive green roof profiles of 300 mm substrate or growing medium. The other four plots were extensive green roof profiles of 125 mm thick substrate. Two of these extensive plots had an aluminium grating installed 150 mm above the surface of substrate, giving an air gap of 150 mm. All green roof plots consisted of a prefabricated aluminium box frame measuring 2.8 m x 4.8 m bolted together. These box frames were fabricated from members measuring no longer than 2.8 m as this was the maximum length for the lift and access through the fire stair well. All materials that were needed for the installations were carried by hand to this rooftop location. Each box framework had 25 mm holes drilled into the bottom of one side and on the lower side for drainage. The aluminium framework was placed on the existing waterproof membrane on the roof slab and then a series of substrate layers were added to construct the green roof system. Green roof installation on 22nd level rooftop

The system consisted of a layer of LDPE sheet over the waterproofing membrane to protect it from damage and then a 25 mm thick plastic drainage cell layer, overlaid with a geotextile layer, then the growing medium and finally a thin 15 mm layer of 7 mm aggregate mulch. At a point half the depth of the growing medium a subsoil drip irrigation system was installed. In three of the six plots a layer of 75 mm Hydrocell RG30 flake was laid over the geotextile layer as a water retention layer, and the remaining substrate was a lightweight soil. The remaining three plots used a proprietary growing medium that contained recycled brick and other inorganic products as well as a lightweight soil mix. All the plots were monitored for water supply and received the same amount of water for every irrigation application. The irrigation was kept to a minimum to reduce any runoff from over watering and to prevent saturating the substrate.

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All materials carried to the roof manually

Installation of green roof layers

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Monitoring methodology

The methodology for this project was to install a series of green roof plots of different thicknesses and monitor them for temperature within the substrate and air temperatures, humidity above the beds and infra-red surface temperature, with comparison to a control space on the original roof surface. This methodology was developed so that the monitoring process could be replicated at a later time or in a different building location for comparison with these current baseline results. Part of the argument for the project was based on the concept that proprietary green roofs currently being used are designed for generic climates that do not have extremely high temperatures (above 40oC) and very low humidity levels (down to 4% relative humidity) as typically occur in Adelaide’s summer months. Therefore identifying an appropriate green roof system and thickness for this climate would provide a base of knowledge for future installation and research. Monitoring irrigation and plant growth

During the monitoring period it was realised that there was a considerable amount of data from which an R-Value or an R equivalent insulation value could potentially be developed. It was considered that this could become an important tool in the design and acceptance of green roofs in this hot, dry climate. The approved project budget allowed a broad spread of monitoring to occur, thus large amounts of data were collected, enabling further research and analysis that was not originally proposed. The green roof plots were monitored for water supply and received the same amount of water for every irrigation application. The irrigation was kept to a minimum to reduce any runoff from over watering and to prevent saturating the substrate. It was used only in the hot summer months. A water quality testing project was developed by a University of South Australia PhD student, consisting of a half pipe with syringe access installed at the geotextile level in the substrate to collect and analyse excess water runoff.

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Green roof heat flow

To understand how heat flows through a

green roof some basic knowledge of heat

transfer is needed: conduction, convection,

evaporation and radiation.

Conduction - The simplest way of moving heat from a hot molecule to a cold one. This is the kind of heat transfer that occurs through a solid material;

Convection - Moving heat to or from a surface by way of a flowing gas or liquid. The rate of heat transfer increases with flow rate;

Radiation - Electro-magnetic heat transfer from all warmer surfaces to all cooler surfaces. Heat radiation can be reflected, absorbed, or transmitted through a surface;

Evaporation – A form of mass heat transfer because heat is removed by taking away hot material. For green roofs this material is water. A characteristic of this type of heat transfer is that material can be cooler than the surrounding air, making the wet surface a little cooler than the ambient air temperature; and

Thermal mass – The ability to store heat in something heavy, like soil or growing medium.

With this basic understanding of heat transfer, these principles can be applied to the many layers that make up a green roof system. See the diagram below.

Green roof system layers

Plant leaf layer – Solar radiation, reflected solar radiation, long-wave radiation heat transfer to sky, convection heat transfer with ambient air, evaporation, conduction heat transfer through roof system;

Stem gap – Shaded by foliage, evaporation, conduction heat transfer through roof system;

Growing medium (substrate) – Thermal mass heat absorbed or released, evaporation, conduction heat transfer through roof system;

Drainage layer – Conduction heat transfer (water), thermal mass heat absorbed or released; and

Waterproofing and roof structure – Conduction heat transfer, thermal mass heat absorbed or released.

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The plant leaf layer and stem gap is a dynamic zone of instantaneously changing temperature, evaporation, and solar radiation and reflection which makes it very difficult to calculate or measure. These two zones have so far proved impossible to calculate for heat flow and insulation value, such as an R-Value, but this is still a work in progress requiring additional measured data to achieve a realistic value. The growing medium or substrate layer heat flow and insulation value can be calculated if the material conductivity and thickness is known. The moisture content of the substrate is an important component, as water is a good thermal conductor. Understanding thermal behaviour in

substrate

To fully understand thermal properties in the substrate of the green roof plots refer to the attachment, Determining and understanding thermal characteristics of green roofs in the City of Adelaide (Clay et al.). The key lessons identified by Clay are:

In an arid climate, green roofs with a substrate depth of between 125 and 300 mm can be very effective in reducing the amplitude of the daily temperature variation on the surface of a roof. This can be up to a factor of ten times in reduction;

Vegetation on the green roof surface works effectively to reduce the amplitude of the temperature variation within the substrate and makes the area attractive to people;

A walkway mesh above the green roof allows access for people but also makes a significant impact on the thermal performance of the roof; and

The role of water in the substrate requires further clarification but it may offer a controllable variable to change the

thermal properties of the beds on demand.

Temperature monitoring instruments

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Roof surface temperature

As shown in the diagrams below for 17 November 2011, at the same time of day there are considerable differences in the concrete roof slab baseline surface temperature for the different profiles. This does not allow for delay in the insulation in the depth of substrate. The deeper the substrate the longer the delay in time for heat flow to travel through the substrate, therefore the shallower substrate shows instant lower baseline temperature for the top of the slab than thicker substrates. More specifically, the distance for heat to travel through the substrate is equal to the square root of time taken. It is interesting to note that over the whole day the 300 mm profile is up to two times more efficient in insulation that the 125 mm plus the grating, or five times better than just the 125 mm profile. Monitoring data in summer shown in the diagram indicates that the concrete roof under the green roof systems can be up to 49% cooler than the control roof surface: 26oC under the 125 mm plus grating green roof compared to 51oC for the control roof surface.

The performance of the 125 mm profile plus grating over the plants exceeded expectations, with an increased insulation value compared to the 125 mm profile without the grating. It appears that the grating provides shading and reduced wind turbulence to lower the surface temperature, thus helping the insulation of the profile. At this height there appears to be no period of calm wind so the protected micro climate becomes important to the temperature profile through this green roof. Also the plant growth was healthier and denser than in the open plots, which might also account for the lower temperatures through evapotranspiration. The grating plays an important role in the insulation and health of the green roof. There is considerable insulation value for the green roof system, not just the substrate itself but the plants and shaded air spaces.

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Air temperature above green roof

The current data shows that the air temperature above the green roof was no different to the air above the control roof. This is surprising, as information from various green roof studies elsewhere in the world and from within the industry generally accepts that the air above the green roof is cooler because of evapotranspiration. In this hot, dry climate a simple explanation could be that the drought resistant plants actually stop transpiration during the heat of the day, thereby reducing the evapotranspiration to a level that does not reduce the ambient air temperature. Another possible explanation is that, given the height of this green roof trial on the 22nd floor, it was observed that there is not any time during the day when the wind is calm. As a result temperature is mixed into the air flux immediately at leaf layer. The air temperature immediately above the green roof does not change, which seems to be characteristic of the hot, dry climate and/or wind movement high up on a multi-storey building. Role of water in the system As discussed by Clay, moisture content of the substrate is important for the insulation value of the substrate, as water is a good thermal conductor. This is also seen in the cross section diagram below showing temperature data for the green roof system, with a rise in temperature at the drainage layer which contains water. Therefore water in the green roof system lowers the insulation value, thus creating a weakness in the green roof system for insulation.

Temperature of water layer in green roof

profile

This suggests that green roof profile design needs to take into consideration water in the profile and to remove it from the profile during the heat of the day so that the green roof can function at its best for insulation value in a low moisture content profile. On the other hand, moisture content could be very useful in removing heat from the building through the green roof system, especially at night time. Clay says, ‘In central business districts, buildings may be high with a relatively small surface area in their roof compared to their wall area. However, walls may still face other walls and heat is then simply reflected (or re-emitted) back and forth with rather little cooling. Radiative emission from roof surfaces then becomes a significant thermal control factor’. This could be managed by using the irrigation only at night in combination with drought resistant plants that do not transpire during the heat of the day.

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There is an opportunity to redesign the green roof profile and its moisture content for hot, dry climates for better insulation performance, and also the opportunity to remove heat from the building at night via the green roof. Developing an R-Value – is it possible? During the data collection stage of the trial, the amount of data being collected indicated that it might be possible to develop an R-Value for the green roof systems. This was further investigated as an additional objective within the project. The process involved looking at the green roof system as a whole – soil/substrate + plants – and then adding this to the roof structure to estimate the potential cooling load reduction. Then this process must be applied to the control roof and the difference between the two will give the potential cooling load per m2 of roof area. The issue is that the R-Value for soil and plants needs to be known. As discussed in the earlier Green roof heat flow section, the plant and stem zone or layers is a dynamic zone of constant change, so it is difficult to develop an R-Value. Now with a better understanding of the issues, future monitoring can be directed to collect the necessary data for this dynamic zone. Work carried out by Clay estimates the substrate values based on heat flow, specific gravity and moisture content. He identified that the insulation value changes with the moisture content, as water is a good thermal conductor. Given the above, Clay developed an approximate R-Value for the 300 mm green roof substrate of 0.6m2K/watt. He has also produced a rough insulation ratio guide for the three green roof plots: ratio of 1 for 125 mm profile, ratio of 2.5 for the 125 mm plus grating and air space profile, and ratio of 5 for the 300 mm profile. Given that the 300 mm is R 0.6, then the 125 mm + grating is R 0.3, and the 125 mm is R 0.12.

These are still only estimates and this does not include any value for the plant and stem space in the total system. Looking at the current data, from another point of view using surface temperatures, then a percentage reduction could be used as an equivalent value. If the control roof surface is 51oC and the 300 mm profile baseline temperature is 30oC then there is a 21oC reduction, or 41%. These figures can be used with the insulation ratios (Clay) for peak outside summer temperatures, as follows:

300 mm profile (ratio 5) equals 41% reduction in surface temperature compared to the control roof in oC;

125 mm plus grating and air gap profile (ratio 2.5) equals 20.5% reduction in surface temperature; and

125 mm profile (ratio 1) equals 8.2% reduction in surface temperature.

The above percentages are for the roof surface temperature that service engineers can use for the insulation value for these green roof system profiles in Adelaide’s hot, dry climate. For example, using the ANZ House concrete slab roof and assuming an R-Value for roof insulation of R3.5, a 150 mm slab of R0.1, plus inside surface of R 0.16, gives a total R-Value of 3.76. Control roof U x (to – ti) = 0.26 x (34o – 23o) = 0.26 x 11o = 2.86 W/m2 300 mm green roof U x (to(temp. in drainage layer) – ti) = 0.26 x (30o – 23o) = 0.26 x 7o =1.82W/m2 In other words, a 300 mm green roof will reduce the instantaneous heat gain by about 63% or 1.04W/m2 compared with the control roof.

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It should be noted that in a multi-storey building this may not result in an overall drop in heat gain because only the top couple of floors will be affected. However, a green roof could be very important for low rise buildings to considerably reduce the heat gain.

Design tool for insulation values for peak

summer surface temperature in oC

300 mm profile (ratio 5) equals 41%

temperature reduction in oC;

125 mm plus grating and air gap profile (ration 2.5) equals 20.5% temperature reduction in oC; and

125 mm profile (ratio 1) equals 8.2%

temperature reduction in oC.

Grating shading impact

The development of an extensive green roof with a grating over the vegetation provides a light weight green roof with high insulation values as well as a trafficable surface. This could be used around plant rooms on building roofs, giving maintenance staff access to equipment as well as the benefits of the green roof. The performance of the grating over the plants exceeded expectations, with an increased insulation value compared to the 125 mm profile without the grating. It appears that the grating provides shading and reduced wind turbulence to lower the surface temperature, thus helping the insulation of the profile. At this height there appears to be no period of calm wind so the protected micro climate becomes important to the temperature profile through this green roof. Also the plant growth was healthier and denser than in the open plots, which might also account for the lower temperatures through evapotranspiration. The aluminium grating adds weight to the profile, but not

significantly - about 7 kg per m2. This is less weight than a ground cover plant.

Aluminium grating with plants growing through

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Plant characteristics

On 4 June 2011 each green roof plot was planted with the same number, species and layout of Australian native plants. The plants were all tube stock size and set out at 600 mm centres and in four rows of each species. There were two ground cover species: Carpobrotus rossii (native pig-face) and Myoporum parvifolium (creeping boobialla); and two grasses: Dianella ‘Tasred’ (flax lily) and Lomandra ‘Nyalla’ (mat rush).

Planting tube stock according to planting plan

The ground cover foliage was about 75 mm diameter and the grasses were about 50 mm diameter by 300 mm high. They were selected as proven species on current green roofs in Adelaide and they are drought resistant waterwise plants, well suited for this exposed site. The plants were fertilised twice in 12 months.

Regular plant maintenance

The plants’ performance was monitored for growth and health every month, usually the first day or week of the month and recorded on site record sheets, as shown on the examples below.

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Examples of plant monitoring record sheets

from April 2012

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The most successful species was Carpobrotus rossii or native pigface, with this species growing to measure 1800 mm diameter on one of the plots. This species was also the only species to be attacked by insects, the white aphid during autumn 2012, which would suggest that the species was under stress. In particular, the pigface under the mesh was more affected, with a likely cause the reduced air movement creating a favourable environment for the white aphids to thrive. Spraying of white oil helped to control the aphids and the pigface regenerated. The grasses only grew to about 450 mm high, but grew considerably in their clumping diameter. The Dianella especially started to spread under the surface mulch to colonise the surrounding area. Plants under the grating were no higher than the plants in the open but were greener and healthier looking than the plants in the open. This would support the concept of a favourable micro climate under the grating. The fertiliser program was two applications of Osmocote ‘native garden’ in 12 months at the rate of 37g per m2.

Carpobrotus rosii in flower in December 2011

Lomandra ‘Nyalla’ in flower in June 2012

Myoporum parvifolium in flower in Dec 2011

Dianella growing strongly through grating

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Water quality

The University of South Australia’s SA Water Centre for Water Management and Reuse (CWMR) was engaged to monitor stormwater runoff from the four green roof plots and to compare this with a control section on the existing roof. The stormwater system for the ANZ House roof surface drainage is a Siphonic Drainage System, which created several challenges in developing a methodology for water sample collection, as described in the CWMR report provided in the Appendix. In summary: ‘The design of the ANZ House green roofs was based on a free drainage system and the designer intended to get rid of excess water from the system as soon as possible after rainfall events. Collecting water samples from the green roof beds was the main challenge in this study. Different methods were considered such as making small scale green roofs at the site, retrofitting beds and adding metal sheet around the beds to collect the water samples. However, none of these methods were feasible due to the building’s operational and maintenance requirements. The only possible way to capture enough water in the porous media was to use half round pipes buried in the soil media. Using the growing media, soil properties and considering the required volume of samples, the diameter and length of the required half round pipe was calculated as 50 mm and 700 mm, respectively. Holes were drilled at both ends of the half round pipe and lengths of hose were attached to facilitate water collection’.

Half round pipe buried in substrate

Hose for water sample collection In summary the findings of the water quality monitoring were: ‘ In this study for the first time in South Australia the water quality from the outflow of two different types of green roof systems were studied during a period of 9 months. Generally the trends of contaminant concentrations in both the intensive and extensive green roofs have decreased during this study period. A comparison between the two types of green roofs shows that except for some events for EC, TDS and Chloride, the concentration of parameters such as pH, Turbidity, Nitrate, Phosphorous, Potassium and Sodium in the intensive green roof outflow were higher than from the extensive green roofs. To examine the possibility of reusing runoff from the ANZ House green roofs in the building, available local, state and national Australian water quality guidelines were reviewed. The water quality of the collected samples with regard to the alternative reuse scenarios such as potable,

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non-potable and urban irrigation were examined. Results show that it is possible to recycle green roof outflow for urban irrigation and non-potable purposes but this source of water is not recommended for drinking purposes’ (CWMR report in Appendix). This research shows that green roofs offer additional benefits for the building’s water infrastructure, both on existing buildings and in the design of new buildings. Reuse of stormwater from green roofs can be incorporated into the building’s non-potable and urban irrigation systems, or discharged into existing stormwater systems when all reuse options have been satisfied. Water use – irrigation

All the trial plots were monitored for water supply using the same type of water meter. They all received the same amount of water for every irrigation application. The volume to each plot was carefully monitored and adjusted to allow for the different drip line irrigation systems that were installed for the two different proprietary green roof systems. The irrigation was kept to a minimum to reduce any runoff from over watering and to prevent saturating the substrate. As mentioned earlier this affects the thermal conductivity of the substrate. The irrigation was used only in the hot summer months. In fact the irrigation was only started on 6 December 2011 and was turned off on 4 May 2012. The water volume was noted every month, usually the first day or week of the month and recorded on site record sheets.

Minimal water runoff from green roof plots

with summer irrigation

The volume of water used per green roof plot in summer was an average of 70 Lt per watering session and in the height of summer there were three sessions per week, equalling 210 Lt per week. This equates to 15.6 Lt/m2/week or 2.2 Lt/m2/day in summer and nil in winter, autumn and spring. This is a waterwise green roof system, especially the 125 mm profile that will survive in Adelaide’s demanding climate with minimal irrigation only in the hot summer period.

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Examples of site water meter record sheets

from February and June 2012

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Findings NABERS: Energy reduction and greenhouse gas emissions Behive Built Environment Sustainability was engaged to develop a methodology and apply this to green roof monitoring data for ANZ House, a NABERS 5 Star rated commercial office building in the City Central precinct – City Central Tower 1 (CCT1). This methodology used monitoring data for summer only (winter heating was not considered) and it only used the green roof profile of 125 mm + 150 mm air gap with the aluminium grating over the plot. This gave a reduction in heat gain through the roof of 4.2 W/m2. The methodology and data are shown in the Appendix, with a summary below. Results related to 1 m2/year of living wall were:

Green Roof Electricity

Reduction in Energy 0.40 kWh

Reduction in Emissions 0.38 kg

Reduction in cost (est.) $0.052

Using the insulation design tool, the 300 mm green roof would be performing far better than the above green roof system, as it is twice the insulation value.

Bees on Myoporum flowers

Providing habitat

Although monitoring the biodiversity of the green roof was not part of this project brief, it was difficult not to observe the impact that insects had on the plant material. For instance a white aphid outbreak occurred after one year of installation, suggesting that it is possible that this is an airborne colonisation. These white aphids were being farmed by ants in the green roof plots, so these ants have somehow found their way to the 22nd level of the building. It was observed that honey bees were using the white flowers of the Myoporum ground cover. This is consistent with other cities around the world such as Chicago where the presence of bees was capitalised upon. Bee hives were installed on the green roof of City Hall and the City now sells honey produced by bees on their green roof. Two species of moths were observed under the leaves during the day time. It could be that they have adapted to the new environment of the green roofs and they may well have already been present, drawn by the attraction of the neon ANZ sign. Also birds have been observed walking through the green roof vegetation looking for things to eat. This would include insects that are attracted to the night light of the signage. The pee-wee or magpie-lark (Grallina cyanoleuca) was a visiting species while we took monitoring measurements.

Pee-wee visiting the green roof trial plots

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Park Island and UHI effect

The monitoring of infra-red radiation over the green roofs produced some interesting results. As Clay states in his report (see Appendix) the infra-red temperature measures total infra-red emitted from the surface. From this monitoring it was found that the gravel surface was reflecting more solar infra-red in the day, whereas the overall surface temperature is increased with the vegetation covering. The vegetation absorbs more sunlight than gravel and is more pleasant for people, since it reduces glare from sunlight and has a low infra-red (heat) reflectivity. This would be similar to the control roof reflecting infra-red but absorbing IR in asphalt surfacing, giving a similar air temperature. If related to the possible Park Island effect within the city’s UHI it is difficult to measure, but the green roof has low glare and IR reflectivity to the neighbouring buildings. The Park Island effect has a limited distance of up to 200 metres, so if green roofs were placed within this distance to one another, or located close to existing green space, this would produce a reduction of ambient temperature. This could be linked with UHI studies of the city, such as that being undertaken by Flinders University. The results of this study are not yet available, so further research is required to develop a planning tool based on that study’s information when it becomes available.

Estimated Capital Costs

300 mm profile green roof costs based on 100 m2 components are: Green roof system (including 200 mm substrate) $250 m2 Irrigation (controller, connections, drip line) included Plants (tube stock, 52 no.) $ 38 m2 Mulch (15 mm thick of 7 mm aggregate) included Total $288 m2 125 mm plus aluminium grating profile green roof system costs: (60 mm soil, 40 mm hydrocell) $230 m2 Irrigation (controller, connections, drip line) included Plants (tube stock, 52 no.) $ 38 m2 Mulch (15 mm thick of 7 mm aggregate) included Aluminium grating $415 m2 Total $683 m2 125 mm profile green roof costs: (60 mm soil, 40 mm hydrocell) $230 m2 Irrigation (controller, connections, drip line) included Plants (tube stock, 52 no.) $ 38 m2 Mulch (15 mm thick of 7 mm aggregate) included Total $268 m2

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Conclusions

The table below summarises the three substrate profiles used in the green roof trials. It describes their attributes and compares them for various rating factors - temperature reduction to dollars, or weight to temperature reduction, whichever factor is the most critical.

Green roof factors

300 mm

profile

125 mm +

grating

125 mm

profile

Saturated weight 290 kg/m2 124 kg/m2 117 kg/m2

Insulation ratio 5 2.5 1

Surface temperature reduction 41% 20.5% 8.2%

Cost $288 m2 $683 m2 $268 m2

Rating tool

Temperature reduction/$/m2 7 33.3 32.6

Weight/temperature reduction factor 7 6 14

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Acknowledgements

This research project was made possible by the South Australian Government’s Building Innovation Fund and Aspen Developments as the industry partner. It was supported by Jones Lang LaSalle and Colonial First State Global Asset Management with provision of the roof space for this work. Fifth Creek Studio’s research was conducted in association with Professor Roger Clay and Neville Wild of the University of Adelaide (thermal monitoring), and Professor Simon Beecham and PhD candidate Mostafa Razzaghmanesh of the University of South Australia (water quality monitoring). We are grateful to A/Professor Veronica Soebarto of the University of Adelaide for her insights into R-Value calculations, to Fytogreen and Junglefy/ZinCo Australia for their cooperation in this research and to Artform Structures for their installation assistance.

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Appendix - refer to separate documents

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