What I'm Seeing Now


Ponding On The EPDM Roof

Ponding on the EPDM roof.

Often over flat roofs we see what looks to be a black rubber surface.  That is a synthetic rubber, produced by the Firestone Corporation, called EPDM.  The acronym means Ethylene Propylene Diene Monomer - an (M-class) rubber.

This material comes in two thicknesses - a 60 mil, the typical thickness installed by builders, and a 90 mil, which is used commercially and by the better roofers for replacement. 

The 60 mil product has about a 15 year life span, maybe more, depending on how much sun it receives.

Typically found on flat, or nearly flat roofs surfaces, like over smaller, front-porch roofs, I find it in various states of installation and condition.

One thing it cannot tolerate is installation directly over a wood sheathing, like Oriented Strand Board (OSB).

It also does not like wrinkles.  It wants to be very flat, and very glued down to a proper surface.  I see wrinkles all the time, a sure sign of unprofessional installation.

One thing the product especially doesn't like is PONDING.  A word never recognized by my computer spell checker, ponding is exactly what it sounds like.  If the roof's sub surface is not smooth, but creates dimples into which water can accumulate, it will do so, damaging the material more quickly.

As water accumulates, small pin holes or slits can develop.  In this case, and perhaps difficult to see in the photo, there is a sizable dimple under the corner rail post.

Evidence of previous, and perhaps current, damage to the front porch column, and the depth of the dimple  underneath, plus the standing moisture since it has not rained in some time, would say that water is getting in where it is not wanted.

Stress on the post's base and surrounding EPDM would say that ponding water is damaging things.  Often I see where these posts are literally nailed through the EPDM to "attach" them to the roof!  Um, you might not want to puncture a synthetic rubber membrane!

Either way, nails or not, this roof surface seems to have reached its normal economic life span.  My job is done.

And what is my job?  To observe and report.

My recommendation:  when you see a flat roof surface, and depending on its age, check it carefully.  But even if new, or newer, don't count on its proper installation and have a careful look.  That is where your home inspector comes in!





Jay Markanich Real Estate Inspections, LLC  

Based in Bristow, serving all of Northern Virginia.

Office (703) 330-6388   Cell (703) 585-7560


Comment balloon 11 commentsJay Markanich • April 13 2012 02:07AM
Ponding On The EPDM Roof
Ponding on the EPDM roof. Often over flat roofs we see what looks to be a black rubber surface. That is a synthetic rubber, produced by the Firestone Corporation, called EPDM. The acronym means E thylene P ropylene D iene M onomer - an (M… more
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