I can’t count the number of times a homeowner has called me to fix a leaking flat or low-slope roof. If you’re a remodeler faced with this situation and you go to the lumberyard to buy materials, they’ll probably sell you 17-inch selvage roll roofing and a few cans of cold patch cement and send you on your way. But if you install a half-lap roof in a climate that gets much weather, chances are in a few years the homeowner will be calling you again. The world of commercial buildings is full of flat roofs, and obviously commercial roofers know how to make a flat roof last for longer than a few years, in any climate. But many of the roofs used on commercial buildings — torch-applied modified bitumen or ballasted systems, where the roof membrane is held in place with stone — are just not practical on residential jobs. Most roofs aren’t built for the extra weight of ballast, and it’s insanity to fire up a torch on the roof of a wood-frame building. As a roofing contractor with a reputation to protect, I wasn’t about to resort to roll roofing for residential flat roof repairs. So out of necessity, I began using EPDM for these jobs: It’s light, durable, and easy to install. And if installed correctly, the product is virtually failure-proof.

EPDM is a black, single-ply rubber roofing membrane. The letters stand for ethylene propylene diene monomer, which describes its chemical makeup. EPDM stands apart from — and above — other single-ply rubber membranes. You may see ads for "rubberized one-ply" roofing or other such names. These are typically types of modified bitumen,...

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