Rather than going with a commercially-supplied green roof, we wanted to do it from scratch, both to learn the mechanics of it and to save some money. We also hope to show that anyone can do this, in an effort to "green up" the city. The basic framework for the roof from a book called "Building Green" by Clarke Snell and Tim Callahan -- a fantastic resource for all sorts of alternative building techniques, as it's one of the rare books of this type to show more than just photos of the finished product.
The first few shots here are concern the demolition of the old garage -- not much in the way of special interest, save that it was a 25 year old building with framing sitting right on the soil -- not great in termite country. It took us the better part of a day to take it down.
Next we've got a shot of the guys building the foundation walls. We contracted this part out -- there was a lot of digging, and while I'm fond of working with concrete, it seemed more prudent (and time-efficient) to have the pros do it. The City insisted we hire an engineer, as this was the first legal green roof garage that they've issued a permit for in Toronto -- and the engineer we hired recommended a full 8" filled block foundation -- if we did it again, I might look to an alternative, possibly a gravel foundation with a ring beam sill. The extra money we would pay in engineering should easily make up for the additional cost of a full foundation wall, and the end product would be greener: less concrete, and water-permeable.
We built the walls on the newly cured slab and tilted them up before adding the roof joists. There is an extra top-plate on the north side to provide slope, and there was already a 1% slope between the tops of the foundation walls from north to south. All the roof joists are 2x10s, that are notched up to 5-1/2" outside the walls. Finally, nailed in some lookouts to get the overhang all around, the king rafters, end plates, and roof sheathing.
Final notes about the roof strata. On top of the roof, we've got an EPDM membrane -- basically thick rubber -- laid loosely over the sheathing and hanging over all 4 sides of the roof. eventually, we will have a thick wire mesh parapet bolted to the end plates and containing all the green stuff: soil, mulch, gravel, landscape cloth and root barrier. The temporary measure is to nail it down with plywood so it doesn't blow away. There is 1" of styrofoam on the membrane, routed every 8" on the bottom to allow for drainage. The styrofoam does double-duty as protector of the integrity of the membrane when we add gravel for drainage (so the membrane isn't pierced), and to protect it in its pre-gravel state from the sharp claws of romping squirrels. The styrofoam is not being used for insulation (which will be between the roof joists), so it being wet is not an issue -- as long as it is resilient enough to protect the membrane, it's doing its job.
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