# recommended EPDM substrate



## jhubert (Nov 18, 2015)

I have a workshop that I've updated with new 2x12 decking with 2x4 purlins and sheet metal roof. Its a 1/12 pitch, roughly 42'x70', with the garage doors all on one gable end. Basically four bays just over 16' wide. I am seeing what I think is mold growth on the underside of the tin, plus the birds/bees are finding all the tiny openings and building homes so Im thinking of taking off the 2x4's and tin and laying down 7/16 zip wall and rolling one big sheet of epdm up and over it (unvented ridge). My dad owns a tractor trailer, and I have a machine/spreader bar to set it on the building...Could you guys recommend your favorite system to work with? Im told the popular thing nowadays is insulation on top of the ply and that those two items can be purchased already bonded. Also this space will only be heated on weekends if that would effect your choice. Any help is much appreciated. I sure dont want to do this roof again!


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## jhubert (Nov 18, 2015)

Anyone out there?


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## dDubya (Dec 21, 2012)

Is your ridge vented now? If not, could that be causing a moisture problem? I have an insulated garage and have to run a dehumidifier if I keep the door closed during the summer. You could always vent it later.

As for what's good under EPDM, we use 1.5" or thicker PolyISO, or 1/4" DensDeck normally.


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## jhubert (Nov 18, 2015)

it is currently a vented ridge tin roof, and Ive found that its low pitch plus some very stubborn bird species means your always maintaining it. I tried stuffing in the precut foam pcs to seal that area but the birds will pull it out to gain access. Between the moisture problems during thick frost nights, the black spot mold, and wildlife infiltration, I wish I wouldve done wayyyy more homework before this tin roof. This past saturday morning it was literally dripping off the purlins:thumbdown:


Does the PolyISO keep the rubber from sweating on the underside?


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## 1985gt (Dec 21, 2010)

It sounds like you have 2x12's as joists and 2x4 strapped across that then the metal roof attached to the 2x'4's? If that is the case condensation will form big time. 

You could if you wanted to salvage the materials is, pull the metal off, pull the 2x4's put plywood over the 2x12's cover that with felt and reinstall the metal. 

Or if you are wanting to insulate and do EPDM you can remove the 2x4's install plywood install ISO then glue down the EPDM. Condensation will not form under the EPDM.

The ISO has to be installed over a solid or semi solid decking, max span for ISO over 1" Is 4 3/8".


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## jhubert (Nov 18, 2015)

Thanks for the info...you are correct I have 2x12 joists on 20" centers (Odd I know) running 16' spans on a 1/12 pitch. I went with 20" centers because over the whole job I saved hundreds of dollars over 16"s and 24"s would've limited my span considerably. Does the 7/16 green zipwall sound sufficient to support the ISO and epdm? And is the ISO board a bit flexible to follow the imperfections in my joists?


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## 1985gt (Dec 21, 2010)

No need for the zipwall, standard 1/2" or thicker OSB or Plywood. The ISO will conform to most imperfections in the decking. You will need at least 8 fasteners and 3" plates for each 4x4 piece of ISO.


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## jhubert (Nov 18, 2015)

:thumbup1:


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