The Green Dream Gets Ready for a Green Roof

Laying down the foundation for my rooftop garden

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 nine-inch-high curbs, made out of 2x4's 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.

[Click here to launch the gallery.

Kama Roof before Going Green
My finished roof with Kama-Eebs panels. I built up nine-inch "curbs" from 2x4s and scraps of ZIP board to make an edge for the garden.John B. Carnett
Layered Insulation for the Green Roof
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
Insulation Washers
These flat metal washers get screwed on to hold down the tapered insulation.John B. Carnett
Insulated Roof
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
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
Rolling Out the Final Layer
The final layer is TPO, a thermoplastic membrane that gets rolled out and glued on top of the DensDeck.John B. Carnett
Gluing Down the TPO
Rolling adhesive onto the TPO before it goes down.John B. Carnett
Ready for Trimming
TPO rolled out and over the curbs, ready for trimming.John B. Carnett
Green Roof Layers
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