A lot of numbers are being thrown around for the cost of green roofs. If you buy a modular grown off site system it can be $45 per square foot. I’ve even heard of systems costing $200/sq.ft.
If you install it yourself with the bare minimum of materials off the shelf it can be $5 per square foot.
The real price for most people is of course somewhere in between.
Consideration number one is what kind of roof exists to start with.
Lets say you need to put a roof system on what is there. Lets say you want insulation (you’d be really stupid not to). Lets say your roof can handle 6 inches of soil. Lets say you want to grow in place (much cheaper).
Here is the layering you’d need and the price per square foot for each item:
1.5″ PolyISO insulation – $0.80
65 mil EPDM rubber – $0.50
EPDM tape, glue – $0.20
3″ XEPS insulation – $2.00
Drainage mat – $0.73
Root Barrier – $0.12
6″ growing medium – $0.33
Sedum and small plants – $1.00
Total: $5.68
Now this is bare bones pricing not including shipping, taxes or waste. But you get the idea: if you are an experience green roof installer in New York and Brooklyn you can get the material costs down this low.
The next question is, why NOT to install a green roof at these prices!