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Why bother with an unsightly and inefficient flat tar roof when you can look out the window at a teeming green garden? That’s why I’m turning part of my roof green. I’ll post more detail about what I’m growing and the DIY tray-based system I’m growing plants in, but before any of that can happen, the roof itself needs to be prepared to hold several inches of dirt without collapsing or flooding my upstairs. For that, I went with a multi-layer system: insulation, rigid roof board and a thermoplastic barrier. Read on for more about the installation and check out the gallery for shots of the roof-prep in action.

I hired a commercial roofing company to take my flat roof system and get it built up to accept my green roof trays. Prior to the roof crew coming, I’d prepared a series of 9-inch-high curbs, made out of 2-by-4s and scraps of the ZIP board I put over the Kama panels. These curbs would hide the edges of the tapered insulation, allow for a wrap around of the thermoplastic layer, hide the edges of my green roof trays, hold my metal caps, and be the top-most edge of my hemlock siding.

The guys apply the tapered insulation by screwing it to the metal in the Kama panels. Then they glue the Dens Deck to the insulation, glue the TPO to the Dens Deck, and finally use high-powered heat guns to weld together all the seams.

The final product makes for a highly durable system that can directly support green roof trays. The multi-layer system costs about $3 more per square foot than a standard flat roof but will really hold up to the abuse of a green roof.

Photo gallery

A finished roof that will soon be a green roof.
The Kama roof before going green: My finished roof with Kama-Eebs panels. I built up 9-inch “curbs” from 2-by-4s and scraps of ZIP board to make an edge for the garden. John B. Carnett
A stack of tapered roof insulation.
A stack of the tapered insulation that gets screwed to the Kama panels. The panels are made of a closed-cell foam core laminated to a glass-reinforced mat face. John B. Carnett
A box of flat metal washers.
These flat metal washers get screwed on to hold down the tapered insulation. John B. Carnett
A building roof with black insulation on top.
The roof with the first layer, the tapered insulation, in place. The slope goes from 6.5 inches to 1/4-inch to direct water to the scuppers, essentially drains that channel runoff to pipes. John B. Carnett
A person using a long-handled nozzle to put glue on a roof, while another person holds a white panel that will go on top of the glue.
Gluing down the deck: Once the tapered insulation panels are down, the next layer is DensDeck, a fiberglass-mat, gypsum-core roof board that gives it a moisture and mold barrier. John B. Carnett
A roll of thermoplastic membrane.
The final layer is TPO, a thermoplastic membrane that gets rolled out and glued on top of the DensDeck. John B. Carnett
A person using a paint roller to put adhesive onto thermoplastic membrane on a roof.
Rolling adhesive onto the TPO before it goes down. John B. Carnett
White thermoplastic membrane on a roof, overlaying the edges.
TPO rolled out and over the curbs, ready for trimming. John B. Carnett
Layers of a green roof, from right to left: Kama-Eebs panels, layered insulation, DensDeck roof board, thermoplastic membrane.
Showing all the layers of the green roof, from right to left: Kama-Eebs panels, layered insulation, DensDeck roof board, TPO membrane. John B. Carnett

John B. Carnett, PopSci‘s staff photographer, is using the latest green technology to build his dream home. Follow along as the project progresses on his Green Dream blog: popsci.com/green-dream.

Sustainability
architecture
evergreen
plants