Make a Sod Roof, the Old-fashioned Green Roof: The Return of the Sod Roof

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OK. Let's assume you properly calculated your new home's roof timbers, you squared everything with the building inspector and the structure is up and ready to be topped. Cover the roof framing with board sheathing or plywood and cover that, in turn, with 50-pound smooth-surfaced or mica-surfaced asphalt roll roofing.

The roll roofing is applied in horizontal strips, starting at the bottom of the slope and working up. The lower edge of each strip should overlap the sheet below by three inches, the lap itself should be sealed with salvage cement and galvanized roofing nails should be spaced every six inches along each lap and around the perimeter of the roof. Once you've worked your way — strip after overlapping strip-up each slope to the roof's peak, apply a generous layer of salvage cement to the entire surface. This sealer is also called double coverage or black plastic cement. Do NOT let a building supply salesman sell you roofing tar.

Allow the cement to dry for a couple of hours. Its top will crust over but the underneath will remain soft and flexible (creating a resilient bed for the sod).

Next, spread a continuous sheet of black, six-mil polyethylene plastic across the dried cement: The poly is available from any agricultural supply dealer and you must be sure to use black (which will last 50 years) instead of clear (which breaks down much sooner). You'll probably have to walk across the plastic as you smooth it down and — i f you do — walk carefully to avoid putting holes in the sheet.

Although not absolutely necessary, it's a good idea to apply another coating of cement and a second layer of black plastic over the first ... just for insurance. There's no need to coat the top of the final poly sheet, however: grass roots will grow through the cement and through the roll roofing, but they won't grow through the plastic.

You're Ready to Lay Sod

The ideal place to get your sod is right from the building site itself. You'll never miss it, there's no closer source of supply and—since sod can be stacked without damage for several months—it should keep in good shape from the time you start your house's foundation until you're ready to put the turf on the structure's top.

Anything from six to ten inches will do, but eight inches is the ideal thickness for roofing sod. The turf should be fairly "tight" and grass is better than weeds (although the latter will do) because grass has a finer root pattern. This tighter root pattern gives grass sod more holding power and insulating qualities (six inches of good turf is equivalent to about three and a ,half inches of fiberglass insulation). Forget any visions you have about growing a small forest on your roof, however, because the roots of trees and shrubs can penetrate the cement, plastic, roll roofing, and sheathing (clearing a path for rain to do the same).

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