45 or 60 ml EPDM under deck/porch floor?
I’ll be using an EPDM membrane under floated decking above an enclosed storage space. I can get a 45 mil sheet 10’x20′ from a local supplier or I can buy a 10’x50′ roll of 60 mil. They won’t cut the 60 mil to the 20′ length I need so I would have to buy the whole roll. Basically I’ll start with a sanded smooth Advantech subfloor and using 2x sleepers with compsite decking floated over the Advantech and EPDM. My question is 45 mil thick enough for this application or should I spring for the 60 mil and stow away the extra? The 60 mil would cost about $320 not including tax. The 45 mil would be about half that. Most of what I’m reading says 60 mil is the best choice and good insurance. I also thought that besides the 45 mil on the subfloor deck that I might could cut leftover strips and adhere them to the bottom of the sleepers in essence ending up with 90 mils between my woods. I guess I could use 2 layers of 60 mil and end up with 120 mils between my woods. Another question is reinforced vs. non-reinforced EPDM?
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I used a liquid waterproofer in my project two Michigan winters ago. No cracks or leaks yet.
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Thanks for the responses guys.
I've never used the liquid waterproofer but would like to sometime. With EPDM, spring for the .060, it's cheap insurance against leaks. The thinner stuff is good for fish ponds.
Glue strips of EPDM to the bottom of your sleepers, as you suggest. Helps limit abrasion.
Most people use 1/2" fiberboard (Homosote) between the subfloor and the EPDM, but it your Advantech is in good shape, won't be walked on too much, and you clean the surface extremely well I don't see the need for the fiberboard.
I've never used reinforced EPDM either, seems like overkill. The regular kind is very tough stuff.
Use the 60. As Mike say's it's cheap insurance. We've done a number of these installs, some close to 20 years ago with no leaks yet. I did use strips under the sleepers for better wear protection.
I use 60mil and strips under sleepers
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What would you expect the service life of an EPDM membrane under decking and sleepers if the porch would never be exposed to direct sunlight?
Jon Blakemore RappahannockINC.com Fredericksburg, VA
I think we could be talking lifetime. Depends on wear and traffic, and how well the seams and flashings are done. There are EPDM roofs forty years old on commercial work, so it tolerates the UV that long anyways. Shielded from UV by the deck it could be longer, but traffic making vibrations, and the actions of grit and ice as well as any potential errors by installers are the variables.Another concern that wanders around in the back of my mind is drips of something like the penofin oil for the wood deck on it. I ask myself can that stuff deteriorate the EPDM?. I don't have that answer. I have done my own short term tests, but that does not tell me if it shortens the life from 40 years to 20 years. All it says is that if I cup some deck oil into a puddle on EPDM for a week, and then pour it off, and play with the same scrap a year later, it is still waterproof.
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I have heard a loss rate of 1 mil per year to UV light. With no exposure, I would think you could get 60 to 80 years no problem. But that is just a guess.
I have heard a loss rate of 1 mil per year to UV light. With no exposure, I would think you could get 60 to 80 years no problem. But that is just a guess.
Even if the actual membrane lasted that long, the seam caulk and adhesive breaks down long before that. I don't know of any .060 EPDM roofs over 20 years old that haven't been coated and that usually only buys a few years before seam failure negates the coating. 15 years seems to be the approx fail age for .045. View Image
Thanks to all for the input.The two decks in question (one I mentioned on my home and one we did on a custom home in 2007) were done with one piece EPDM sheets. So any seam issues are a non issue with the roofs in question.We did put scraps of EPDM under the sleepers but I honestly cannot tell you the thickness (45 or 60). I will check a scrap left over to see if it's written on the back.
Jon Blakemore RappahannockINC.com Fredericksburg, VA
Another vote for 60-mil, and yes, glue strips of the stuff to the bottom of the sleepers.
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