[charlieqin]

I am from Beijing,China. Not long ago,I worked with a developer who had a concept as follows:

Over a lake of 300 Mu of land a developer plans to build a 2 story structure (a trading market) and on the roof of the structure to save land for the local farmers, grain,vegetables,trees,flowers and etc can be grown or planted as they were in the past.The earth fill-in on the roof he asks should be as thick as 3 meters,good enough for any plantation when the project is completed.

Is this concept feasible or workable technically? Can the structure support the weight of the roof, to say nothing of water proof and etc?

Thank you.
Charles Qin:banana:
Beijing,China
www.partyapartyb.com (http://www.partyapartyb.com)

[mthd]

the 'green' roof concept is well established and the engineering challenges are certainly not insurmountable.

there are two kinds, generally referred to as intensive and extensive. an extensive roof uses a kind of plastic grid or tray with just a few inches of soil and water capacity in which certain types of grasses will grow. these are very effective at buffering the flow of water into storm systems, etc.

what you are referring to would be an intensive roof, which is essentially a normal roof with increased bearing capacity and several feet of soil dumped on top. 3 meters is very excessive and unusual - 1 meter would be more common. whether this could support long term farming is probably an unknown, but small scale gardens, parks, etc, are a feature on many urban roofs.

[BTinSF]

This is the new California Academy of Sciences in Golden Gate Park, designed by Renzo Piano. While the roof is designed mainly to be "green" and grow native grasses, flowers and other plants, I see no reason it couldn't grow food crops:

http://www.aia.org/aiarchitect/thisweek06/0609/0609pw_cas1_b.jpghttp://www.aia.org/aiarchitect/thisweek06/0609/0609pw_cas2_b.jpghttp://www.aia.org/aiarchitect/thisweek06/0609/0609pw_cas4_b.jpg
Project Name: California Academy of Sciences
Year: Current
Client: California Academy of Sciences
Location: San Francisco, CA, USA
Building Type: Educational
Greenroof Type: Extensive
Greenroof System: Custom
Roof Size: 160000 sq.ft.
Roof Slope: 65%
Access: Inaccessible, Public
Submitted by: Greenroofs.com & Rana Creek

Designers/Manufacturers of Record:
Greenroof Consultant: Rana Creek Living Architecture
Ecological Consultant: Paul Kephart, Rana Creek
Architect: Renzo Piano Building Workshop
Architect: Chong Partners Architecture
Engineering and Sustainability Consulting: Arup
Landscape Architecture: SWA Group
General Contractor: Webcor Builders

[BTinSF]

what you are referring to would be an intensive roof, which is essentially a normal roof with increased bearing capacity and several feet of soil dumped on top. 3 meters is very excessive and unusual - 1 meter would be more common. whether this could support long term farming is probably an unknown, but small scale gardens, parks, etc, are a feature on many urban roofs.

Do you happen to know how deep the soil is in Yerba Buena Park on top of Moscone Center?

This "garden" is actually the roof of the San Francisco convention center "Moscone Center":

http://www.yerbabuenagardens.com/img/gar-esplanade-30-19CD1.jpghttp://www.yerbabuenagardens.com/img/gar-08indian.jpghttp://www.yerbabuenagardens.com/img/gar-10-butterfly-garden.jpghttp://www.yerbabuenagardens.com/img/ybg_web_4.jpg

While again, here, everything is decorative, I don't see why it couldn't be edible crops.

[mthd]

i don't know offhand the soil depth at ybg - but i would suspect it's significantly less than a meter except in isolated locations...

the only thing i wonder about with heavy farming is whether isolated pieces of soil would become depleted in the minerals extracted by certain crops too fast. there's no adjacent soil to draw from so maybe you would have to rotate pretty heavily. i'm sure that household gardens wouldn't be a problem, but actual agriculture might be difficult.

[BTinSF]

i don't know offhand the soil depth at ybg - but i would suspect it's significantly less than a meter except in isolated locations...

the only thing i wonder about with heavy farming is whether isolated pieces of soil would become depleted in the minerals extracted by certain crops too fast. there's no adjacent soil to draw from so maybe you would have to rotate pretty heavily. i'm sure that household gardens wouldn't be a problem, but actual agriculture might be difficult.

If crop rotation and fertilizer couldn't solve the problem, you might have to replace the soil periodically.