The hardest part of building a living roof, other than figuring out how to get all that monstrously heavy soil or sod up there, is designing a good edge detail that will contain the soil at the eaves and gable ends. A good living roof edge detail should contain the soil on the roof, while simultaneously allowing the excess rainwater to drain off, all without puncturing your liner, and allowing for some kind of gutter system. And it should look decent. That’s a lot of design details to weigh, but I think we developed a good set of plans. Check it out.
Plans for a Good Living Roof Edge Detail
The main components for our edge detail are the following:
- metal flashing, 8″ wide with a 1.25″ bend
- 5″ corner braces
- 5.5″ wide white oak boards (1″ thick)
- roll of galvanized steel flashing
- 1″ zinc-coated SPAX screws
- 3/4″ screws of your choosing
- 1″ galvanized roofing nails
As I mentioned above, you need to allow excess rainwater to easily leave your roof, all while holding the soil back at the edge. What we devised was a soil retaining board, in this case a 1″ thick white oak board, wrapped in steel, fastened to the roof deck about 1/2″ off the surface, with a gravel dam on the soil side to filter water. The retaining board is fastened in such a way that there are no punctures in the liner, and water should find its way into a gutter easily.
Note: the theory here is that the retaining board does not actually do that much work. Gravity does the overwhelming majority of work, holding the soil in position on the roof — the retaining board mostly keeps stuff from falling off at the very edge. In no way is this edge board responsible for holding all of the weight of the soil on the entire roof surface. (And for the record: the roof on Gobcobatron has little (if any) edge board to speak of, and the sod stays put quite well, thanks to gravity alone.)
Here’s a stunning technical drawing that I made up in Photoshop to demonstrate the different layers and components:
And here’s another look at the real life version:
And here’s a bit more of an explanation of the details:
- The 5.5″ inch wide white oak board (white oak is highly rot-resistant, hence our choice for that particular wood) is wrapped in metal. We used a roll of 8″ wide galvanized steel flashing (it’s more durable than aluminum). You could get pre-bent trim coil for the purpose, but we went the hard way. (A metal break would have went a long way here, too.) We fastened the metal with 1″ galvanized roofing nails (had to pre-drill for every one), spaced 3″ apart.
- We bought a pile of 5″ corner braces, and installed those to the now-wrapped oak board every 24″. We used a 1/2″ shim between the board and the corner braces to ensure there would be a gap. This gap is how water leaves the roof surface once the assembly is installed on the roof. We chose zinc-coated SPAX screws to install the corner braces – they look neat, and drive cleanly.
- We cut the EPDM pond liner along the edge of our roof decking with a pair of scissors.
- Next, we folded back the pond liner, and installed the 8″ wide flashing (with 1.25″ bend). We used 3/4″ screws to secure the metal to the decking. We positioned the metal so the 1.25″ bend was about an 1″ (or finger’s width) from the surface of the fascia. The gutter should tuck right behind the metal, so water can run right off the flashing, into the gutter, and into a cistern.
- We lifted the edge board into position, set back a couple inches from the edge of the decking, and screwed it into position.
- We tucked the pond liner over the corner braces, and under the 1/2 gap between decking and retaining board, and cut out the EPDM that interfered with the corner braces.
- Finally, we spread a layer of gravel against the retaining board to act as a filtration layer. (Some of the smaller gravel will fall through the 1/2″ gap, but that’s fine.)
Make sense? I hope so. The goal was to, at no point, allow water to go anywhere but straight down, into the gutter, without making contact with wood. The gravel should help keep soil out of the gutter, as well.
As for the gable ends… those are a bit easier. We used the following items to devise an edge:
- 8.5″ wide white oak boards, with a 30 degree taper cut at the bottom edge
- 5″ wide flashing, with a 1″ bend
- 3″ screws
- 3/4″ screws
In this case, the steps were fewer. We cut an angle at either end of the board to match the pitch of our roof. A 30 degree rip cut along the bottom edge adds a nice bit of flair to the design, as well as a little custom cut at the bottom ends (see image below to understand better).
We put a chalk line about 2″ from the top of the rafter, and installed the white oak board with 3″ screws, being sure that we didn’t pinch the EPDM pond liner between board and rafter. Next, we cut the pond liner, flashing it up the board, but not over. Finally, we used the 5″ wide flashing to trap the liner against the wood, and used 3/4″ screws to keep the metal snug against the wood. Very simple, and the metal + EPDM creates a double barrier against moisture here.
At the top of the gable, we took the opportunity to add a nice bit of extra flair, too.
And there you have it! That concludes this living roof edge detail design…. something that has consumed me for a long, long time. Information and specific details are very scant out there. This page has a few termination details of its own, but otherwise, there is little detail out there.
I think this is a fairly slick solution.