Thursday, September 18, 2008

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.


Blogger joel and stephanie said...


We recently did an EPDM roof on our 2nd story sleeping porch and also had some bubbles. We use water based adhesive that did not need to be dry to the touch ... but we did also have some bubbles. You may want to take some 1" blue foab board pieces and use them to cusion a floating deck over the EPDM to walk on. That is what we are doing and will cut the joists so the deck is level.


P.S. finished my first night of flooring. my back hurts

September 18, 2008 at 9:31 PM  
Anonymous anita and jack said...

When will you learn Thomas??? Always, read the instructions. The place looks great. I promise not to wear high heels when we come up for the tour.

September 19, 2008 at 2:44 PM  
Blogger oldmilwaukee said...

A&J, I usually read the instructions, but then I veer "off label". Sometimes, not for the better.

J&S, I might put some kind of reinforced astro-turf mat on the balcony and dare the kids to step somewhere else. :)

September 19, 2008 at 6:11 PM  
Anonymous Rman said...

Thanks for the blog about your incredible home. I could not stop reading until I looked at every one. You made a good choice using EPDM. I put an EPDM flat roof on a 2nd. floor balcony (13' X 13')at my house, built in 1984, and the original rubber is still functional. I believe it was 30 or 45 mil rubber. I have acquired a piece of 90 mil rubber, left over from a remodeling project, to replace it if the need arises. Be careful with your roof drains. You need to maintain them to make sure that they stay unclogged. Also, they may be undersized in case of torrential rains, especially until you get gutters on the house. You may want to provide scuppers, in case the drain capacity is exceeded. I used a commercial style cast iron drain, with a 4" outlet, and a half dome grate. The grate needs to be cleaned occasionally, or it can get clogged up.

September 24, 2008 at 8:16 PM  
Blogger oldmilwaukee said...


Thanks for taking time to post with your experiences. I am not sure how thick this rubber is, but I would guess about 60 mil or better. Glad to hear that it has lasted a long time for you.

I think you are correct that my drains are undersized. If I could do it over, I would make them bigger. The limiting factor is the little 3/4" pipe that we put in the stone wall. I am thinking about buying a temporary section of gutter to divert the main roof runoff until I get time to put proper gutters all the way around the house. If I don't get to it before the first good rain, I'm going to sit up there and be ready to bail! :)

September 25, 2008 at 8:39 AM  
Anonymous Anonymous said...

you might consider floating some synthetic decking (2 the long way then the layer you actually stand on the short way) as other similar applications where only flat soled workers had access to the roof of foam/ruber there were eventually some "stretches" that leaked because of the underlying softness of the foam.

Love your project! May I lobby for an open house when this is "completed" Of course we will bring house warming gifts. :)

September 29, 2008 at 7:31 AM  
Anonymous Liquid Rubber Videos said...

Liquid EPDM is best for any kind of roof repair since it can be used for any roof having any shape.

July 8, 2010 at 5:01 AM  
Anonymous bob said...

I had a tile shower leaking on a house I bought about 6 yrs ago. Had a contractor in and he used liquid epdm. 2 months later it was leaking. Stripped everything off and then thought, I see old boats that are 30 plus yrs old and still float.

So I bought fiberglass supplies and the contractor and I fiber glassed the entire shower stall 1/4 to 3/8 thick then placed the tile on top of that and finished it off. No more leaks. I'll never use epdm again. Fiberglass ROCKS for this.

I would have laid down a layer of fiber glass (cloth and resin) on your floor/roof building it up to 1/4 - 3/8 inch thick then to finish it I would have got some course sand and mixed that up with liquid resin (keeping it as thick as possible) and spread it on the floor to finish it off. You could also have laid down tile/grout over this or thin layer of stone with grout like I did in my shower stall.

Non slip and sealed once and for ever.

November 8, 2010 at 1:35 AM  
Blogger Richard said...

It really is hard to do a DIY EPDM flat roofing project if you don't have a professional to guide you on every step you do without screwing up. I had our old flat roofing in Miami, FL replaced, since the last owner of our house had their flat roof all messed up badly, and for a few years now, we still haven't detected anything wrong with the job.

November 18, 2010 at 11:46 PM  
Anonymous Brendan Gertner said...

Wow, your house totally looks like a castle! And I like your decision to go for EPDM as a waterproofing tool to easily channel the water on your balcony roofing. At my place in Vancouver, BC, I am totally vigilant for my roof's rigidity, due to seeing others' roof getting beaten up by the storm, that's why I am regularly having my roof checked by the Richmond roofing contractors before a major storm.

March 3, 2011 at 9:37 PM  
Anonymous Los Angeles Replacement Windows said...

It resulted in a great combination of modern and medieval. Excellent work.

@Rman, I had the similar experience wit the half dome grate. It does kind of requires a lot of tedious and regular cleaning, and a lot of getting used to.

March 6, 2011 at 10:00 PM  

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