Green roofs could enhance Hong Kong environment

Creating green roofs is at once an obvious yet modern idea; HK has only few green roofs as yet, but surely there are large areas of rooftops that could be greened, and so greatly enhance the city.

Here's some info I've been sent by Gene Wan - who has also sent me several books on green buildings, which I could lend people who might be able to make use of them. He lives in Seattle; has seen some green roofs there.

When designing a green roof, it is important for the roof designer to get in early on the general building design process. The green roof designer needs to know the dead load capacity of the roof above the roof deck, i.e. the weight the roof can support less the weight of the roof deck, the roof structure and any items hanging from the roof.

The weight of a green roof includes the weight of its components: waterproof membrane, retaining grid for growth medium, the growth medium at full depth and saturated, mature plants, irrigation systems and border materials. The main variables are the depth and type of growth medium and the plants used. The membrane materials and growth medium locking grids are changing with advances in technology.

Given a clean roof deck, green roofs slightly larger than Seattle Tilth's [i.e. about 90 square meters] can be installed in about 4 person-days. The timing of planting is important. Green roof construction can be paused after the membrane installation until the weather is conducive for new plants to take root.

Smaller green roofs for residential buildings usually weigh less per square foot than for larger buildings, and because of their lower height, are more prone to weeds. Because of their sheer numbers, however, residential green roofs have more environmental impact potential than large building green roofs.

Advantages of green roofs include:
- Possible water remediation of toxins in rainwater or roof irrigation water
- Reducing severe levels of storm runoff. To my surprise, this was the most beneficial effect of green roofs.
- Possible food production
- Noise reduction by up to 15 dB
- Reduced building cooling load by up to 30%
- Provide habitat for beneficial insects, birds and other wildlife
- Are more resistant to UV light and last longer than asphalt roof materials
- Collectively, green roofs reduce the heat island effect of large cities. I did some research and found a web page by the EPA that had some interesting information:
- Beautify an urban environment.

I may have given you Mr. Carey's website before but here it is again:
He has had an interesting career including teaching and designing green roofs in Florida and Kuwait.

He recommended the following book:
Planting green roofs and living walls
Nigel Dunnett and Noël Kingsbury.   
Portland, Or. : Timber Press, 2008. [2nd ed.]
ISBN:   9780881929119, 0881929115
The second edition includes green roof designing software.
You can view my videos about the Seattle Tilth green roof at:

I am planning more videos of other demonstration sites in the coming months.

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Martin Williams's picture

Another email from Gene:

I've stopped working on the latest videos and posted them at:

I believe this project more than others here, exemplifies the potential a green project has in attracting visitors.

Your colleagues may also be interested in an upcoming green roof project at the Van Dusen Gardens in Vancouver, British Columbia, Canada:
The Van Dusen Gardens is one of the most popular gardens in

I feel early green roof and sustainable building projects have more novelty than later projects and so have a larger potential to draw visitors. Further, I think I can safely say the Hong Kong Wetland Park is too commercial to be taken seriously by most Westerners, at least, as an environmental venture.

If anyone has questions about the Seattle Public Libraries green roof partnership project they can view the branch website:

Martin Williams's picture

Via google, just come across this page, which well worth a look I believe:

8 Great Green Roofs: A Brief Pictoral History of Compelling Green Roofs and Roofing Systems