Thread: Water pooling on flat roof

Do you report this, water pooling on EPDM flat roofing.

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Typically if the water is gone within 24 hours then it is not an issue. That is how design specs usually read.

I would consider it a failure of the preparation of the under deck. There really should not be any pooling if the roof were sloped correctly. That's a pretty big "birdbath". Any pooling puts an additional strain on the roofing system. The accumulation of silt as a result of the pooling can become acidic as well, at least around here in Los Angeles. That can attack the roof covering and weaken it IMHO.

Originally Posted by Henry Henchal

Typically if the water is gone within 24 hours then it is not an issue. That is how design specs usually read.

I've heard this and similar guidlines over the years and they always kind of bug me. 24 hours when? Summer? Winter? In the shade? Sun?

Of course, just about every flat roof I've seen collects water that lasts more than a day or two. I usually write them up and explain it increases the chances of leakage and can wear out the roof quicker. In my experience, every flat roof leaks. It's not a question of it but when.

I see it all the time, and write it up all the time. It's kind of a "don't call me if it leaks there" kind of thing. I look for leaks under the area, which there are signs of frequently. I then explain that if it's not leaking now it may in the future if water is collecting there.

Also, I believe that is a PVC roof in your photo, not EPDM.

I think that the ponding there is notable. There also seems to be deflections between the support framing. I would have recommended that it be checked out. It would at least take any potential monkey off my back.

A duck could have bathed in that. Deflection indeed, and the roof is only 4 years old.

Originally Posted by Jim Robinson

I see it all the time, and write it up all the time. It's kind of a "don't call me if it leaks there" kind of thing. I look for leaks under the area, which there are signs of frequently. I then explain that if it's not leaking now it may in the future if water is collecting there.

Perfect, always write it up!

All flat roof pooling gets written up in my reports.

A professional roofer would have built up the underside of the EPDM so that all roof water gets conveyed off the roof surface.

Here is the roof a a condo I did a while back. The roof had been converted to a duck pond.

That thing is an assisted living complex for geese

That's the good thing about PVC membrane, which this is, on flat roofs. As with another comment to ponding duration (i.e. not more than 24 hrs.) that's good too. You don't want a masquieto pond. Seriously, it's never desirable to pond water, but flat roofs do that in spots (I hate that). It's when it ponds enough, and towards the center of roof spans, to cause a loading problem - this doesn't.

Yes, I call it out...but call it ponding...not pooling. I don't try to indentify the exact material, choosing instead to refer to it as a single ply membrane roof covering. Here's a pic from one this past week.

I'm surprised how many people think these roofs are walkable surfaces. Also how many leaks did you find around those post?

Originally Posted by James Duffin

I'm surprised how many people think these roofs are walkable surfaces. Also how many leaks did you find around those post?

I've seen it a lot and it rarely ever goes well.

The OP's picture also shows staining proving this ponding happens regularly and certainly lasts 24+ hours.

Originally Posted by mathew stouffer

Do you report this, water pooling on EPDM flat roofing.

I believe the international building code states flat roofs should be dry with in 48 hours after precipitation ends. it does not say for which season.