The Potential for Retrofitting Green Roofs in the Central Business District

The 16th Annual European Real Estate Society Conference, Stockholm24-27 June 2009

Sara J Wilkinson, Dr Kimberley James & Prof Richard Reed

Overview • What is a green roof?• What are the benefits of green roofs?• What are the problems with green roofs?• What are the building attributes required for retrofitting green

roofs?• Research question & Research methodology• Research findings• Final thoughts

Why do we need to retrofit green roofs in the CBD?

1. The drive to increase sustainability of existing building stock 2. One option is to retrofit a green roof. 3. Australia needs to increase the adaptation of the existing commercial

property stock to reduce building related ghg (CSIRO, 2002). 4. City of Melbourne authority plans to be carbon neutral by 2020 (Arup, 2008). 5. 1,200 building adaptations to deliver the 24% greenhouse gas reductions to

existing buildings. 6. Some of these carbon emission reductions could be achieved through the

provision of green roofs. 7. By 1996 Germany had over 10 million sq. m. of green roofs: is Australia

missing an opportunity for sustainability?

What is a green roof?

• a roof that uses plants• aka eco-roofs, nature roofs or roof

greening systems• intensive or extensive• Intensive provide gardens for people• Depth of substrate varies• Hybrid – semi intensive• Critical success factor is keeping the

plants alive – is this an issue in Australia?

What is a green roof?

What are the benefits of green roofs?

What are the problems with green roofs?

Technology around for 20 years: why are there not more green roofs in our city centres? 1. Lack of awareness -developers, poor appreciation by government officials and

general public2. Few incentives support green roof - Basel, Switzerland*3. Higher construction costs - double standard roof. 4. Market does not recognise or account for the benefits of green roofs, and rather than

adopting a life cycle assessment the economic case only is considered. 5. Adopting new methods and techniques 6. No long-term documented examples 7. Claims of lower maintenance costs appear reasonable – no evidence 8. When green roofs are adopted within building codes and technical standards -

confidence will be enhanced.9. Possible some undesirable birds or invertebrates might make green roofs their

homes. 10. Technical data limitations - the range of benefits achieved varies according to a

building’s location, climate and construction type.

What are the building attributes required for retrofitting green roofs?

Research questionsWhat is the extent of the potential to retrofit green roofs within the city of Melbourne central business district (CBD)?

• The aim to undertake a comprehensive audit and examine the CBD commercial building stock to identify the number of buildings which contained the attributes or characteristics required for green roof adaptation.

• Melbourne is fairly representative of a major global city in a developed

country

Research methodology• Database – CLUE, PRISM, Heritage, PCA, Google Maps, visual survey• The criteria listed below are typically taken into consideration when

determining whether a roof is suitable for retrofitting with a green roof: – Position of the building– Location of the building– Orientation of the roof– Height above ground– Roof pitch– Weight limitations of the building– Preferred planting– Sustainability of components– Levels of maintenance.

City of Melbourne

CBD

Research findings

Research findings

Research findings

Research findings

Research findings

Research findings

Research findings

Research findings

Research findings

Research findings

1. Only 15% of the 526 buildings were considered suitable for green roof retrofit

2. Only 3.1% are north facing, are not overshadowed and suitable for green roof adaptation.

3. Low secondary locations offer highest potential for green roof retrofits.

4. Ungraded stock and B grade stock are least likely to be overshadowed.5. Concrete framed stock is more suited to extensive green roof retrofit.6. The highest amount of stock which is not overshadowed is in private

sector ownership.

Final thoughts • Social, economic and environmental arguments are convincing • Barriers to uptake exist • On a physical assessment potential for retrofit is very limited • Most likely to be low secondary locations, ungraded or B grade buildings,

privately owned, concrete framed and not overshadowed • Only 78 appear to be suitable • This limitation is compounded as most physically adaptable stock is

privately owned • Limitation 1 - three of the nine criteria for green roofs were not

considered as they outside the scope of this research which was to establish the physical potential to retrofit. This is a minor limitation.

• Limitation 2 - no structural calculations were undertaken to assess roof loads because of the time and costs. Structural suitability has been assessed on whether the building frame and roof is constructed of concrete and also based on a retrofit with an extensive (i.e. lighter weight) green roof.