EPDM Flat Roofing

This little turret feature on the outside of our house was not in the original design. It was just something I decided to do when I realized it could be done and it would look neat. The stonework has been done for a year, but I've been putting off building the flat roof (aka bath-tub roof) that must go inside of the balcony.

I don't know how they waterproofed flat roofs on castles five hundred years ago (maybe they just lived a damp existence), but for this castle-like part of the house, I chose EPDM. EPDM looks and smells like the truck inner tubes we used to sleigh ride on when I was a kid. EPDM is not really considered a DIY roofing technology. In fact, it's used pretty much exclusively in commercial applications. However, I did find some discussion on the internet from folks who had re-roofed their RV's or lined their ponds with EPDM.

Because the topology of the balcony is more like a bath tub than a roof, it was necessary to put drains in the roof. When the stonemason and I built the tower, we thought ahead and mortared in two pieces of sunlight resistant 3/4" pvc. The 3/4" pvc is laid horizontally through the wall, so I needed to turn a sharp 90, and seal the pipe through the EPDM. Naturally, I bought two bath tub drains to get all the pieces I needed (with pieces left over!).

EPDM can be glued to OSB or, as I chose, directly to polyiso insulation. I built up a floor (sorry, I'm using "floor" and "roof" interchagably) for the balcony with 2x4's and put 4" polyiso insulation on top of that such that the top of the polyiso was level with the floor drains. Of course, I slanted the floor (roof) so that water would flow to the drains. The sliver of wood that you see in the picture is there to fill a void and keep the water from pooling in the corner of the roof. (It was not possible to put the drains exactly in the corners.)

I bartered with my friends at North Coast Roofing in Huntington, WV to get a scrap piece of EPDM big enough to do the whole balcony without a seam. I cut the holes for the drains and test fit the sheet of rubber before uncorking the glue. This glue is some mystical stuff. (I'm not just talking about the colors you see after breathing the fumes for a few minutes.) The instructions say to coat both surfaces and let it dry until it is tacky. But by tacky, they mean "not sticky or stringy when touched with a dry finger." I got myself into a heap of trouble and wasted several hours by not following the directions exactly. (remember, technically this is not a DIY product... the manufacturer assumes you are a professional.) I got impatient and stuck the surfaces together while the glue was still "tacky to the touch." I reasoned that it would be easier to position the rubber if the glue was still a little wet. Bad idea. If the glue hasn't cured before the rubber is placed down, then the glue will probably never cure and you will have bubbles galore. That is what happened to me.

Disgusted with all of the wrinkles and bubbles, I tried pulling the rubber back up. Guess what, the rubber came back up... but it pulled the fiberglass backing right off of the polyiso! This glue is some tenacious stuff. I quit for the day and came back this morning to tackle the whole gommy mess again. With half a can of glue left, I tried gluing the rubber back down again. Actually, the rubber was stuck to the fiberglass facing, so I was really glueing the facing back on to the polyiso insulation. This time I followed the directions on the bucket of glue, letting it dry before sticking the rubber down. Miraculously, it worked. I'm definitely not ready to do this for a living, but now I think I could recognize a crappy rubber roof job if I saw one. (it would look like my first attempt!) Because there's nothing but dense foam insulation directly under the rubber roof, I need to put a sign on the balcony forbidding high heeled visitors from stepping on to the roof!

Using tap-con screws, special mastic, aluminum termination strips, and more of that insane glue, I ran the rubber up the insides of the balcony approximately 3.5" and secured it to the stone. This last picture shows the final job after I poured a gallon of water into the balcony as a test. Water gushed out the drains just as I had hoped. Now to find some spitting gargoyles to place on the outside of the tower right where the water exits!

My wife (wisely) implored to me to discard the drain plugs that came with these drains... lest our youngest son find them and make a birdbath for himself on top of our tower.