We just installed the green roof on the Brooklyn Green Show House. Here are the material costs to build a green roof on a Brooklyn brownstone.
Total Roof area 600 sq.ft.
Green Roof area 500 sq.ft.
This stage is about getting as much insulation and waterproofing on as possible. A green roof gives good cooling in the summer but not much insulation in the winter. Thus the added insulation. Lay first the Poly insulation, then EPDM rubber waterproofing membran and then the XEPS waterproof insulation. This also creates a cushion for the EPDM so it is not punctured. The EPDM has shown in studies to be an excellent root barrier, although we have a second one just in case.
1 1/2″ Poly ISO $750
EPDM and caulking $500
2″ Extruded Polystyrene (XEPS) $550
Total for roof prep: $1750
In order bottom to top.
Water retention mat $200
Drainage mat $300
Root barrier $80
Soil in burlap bags, compost, wood chips $500
Around the roof a 1′ border of decking $200
Green Roof Total: $1780
This comes out to $7/sq.ft. for a 3″ deep sedum green roof garden with excellent insulation and waterproofing membrane. If installed correctly this roof could last 50 years. Good installation and waterproofing is key. The energy savings during heating and cooling months will be noticeable.
Of course the ecological and lifestyle benefit of a green roof on a Brooklyn brownstone is obvious. Financially, viewed from the heating and cooling savings and the extended longevity of the roof it makes a lot of financial sense to install a green roof as well.
What is not included here is the labor, which is hard to gauge because we had a lot of students and interns who were eager to learn through experience. It took longer than a normal install because we took our time in the educational process. But the roof prep takes a couple days and then the green roof another couple days with a crew of four proffessionals.