How To Look At A House
McGarry and Madsen's home inspection blog for buyers of
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What is an EPDM roof?
Tuesday, October 9, 2018
EPDM is an acronym for Ethylene Propylene Diene Monomer. It is an elastic synthetic rubber, manufactured in large sheets, for installation on flat and low-slope roofs. EPDM is typically sold in rolls 10-feet wide and up to 100-feet long, that are laid out in overlapped rows with glued seams, forming one, unified single-ply waterproof membrane when completed. It’s available in both black and white.
Although EPDM is most often used for commercial buildings, we occasionally see it on flat and nearly-flat residential roofs, as an alternative to modified bitumen and 4-ply built up roofing. The whole assembly is glued to the roof surface in most of the residential applications we see, but it may also be secured using plastic cap fasteners or ballast. The perimeter is secured with metal strips screwed in place. EPDM is also popular as a liner for garden ponds.
Problems with an EPDM roof, when they occur, are usually related to poorly glued seams or foot traffic on the roof. Installers have to take extra care to make sure any debris is removed from the roof surface before the EPDM is laid down, to avoid punctures coming up through the material later on when the roof is walked on. Fortunately, any small punctures or tears that develop can be repaired with a small patch piece and glue, similar to repairing a hole in a tire inner-tube.
We occasionally see EPDM used when a deck is built over a low-slope roof. It’s important not bear the joists directly on the EPDM and to provide adequate drainage when a deck is added. A roof deck we inspected a few years ago overlooking the Gulf in Steinhatchee, Florida, ignored both of those basic principles, and ended up with stinky standing water that detracted from the spectacular gulf view at the railing. The holes drilled in the fascia board (shown in the second photo) appeared to be an after-the-fact fix that didn’t help at all.
One little-known advantage of EPDM: it does not leach any contaminants into the rainwater that flows over it and off the roof, unlike asphalt/bituminous roofing, and can be specified for “green” homes with rainwater catchment systems. The bright white color also qualifies EPDM as a “cool roof.” Go to our blog post What is a "cool roof”? to learn more about its advantages.
EPDM is advertised as having up to a 40-year life, but our experience has been that the material lasts 20 to 30 years in the Gainesville area. For more information about EPDM roofs we suggest visiting the EPDM Roofing Association website at www.epdmroofs.org.
A similar and competing roof material that is becoming more popular in the last decade is TPO, which is an acronym for Thermoplastic PolyOlefin. See our blog post What is a TPO roof?
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To learn more about roofs and attics, see these other blog posts:
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