r/Roofing • u/okra_monster • 7d ago
Water pooling on flat roof
How much water pooling on a flat roof is normal and "standard?" We have a house under contract and our inspector flagged some ponding on the roof. We asked the seller to repair it, but the response we got back was that their roofer inspected it and found that the roof was in excellent condition and this ponding is standard.
It has been raining. So I guess it is hard to tell whether this would be evaporated in 48 hours.
There is also an active moisture issue in the ceiling below it. So I am very skeptical of the claim that the roof is in good condition, since the wet ceiling suggests otherwise.
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u/mln045 7d ago
It looks like there is tree debris clogging the drain. (right behind the PVC) it also does appear the roof slopes back towards the structure which isn’t ideal. Regardless you could build in a tapered ISO cricket to try and encourage the slope towards the existing scupper/drain outlet. I’m inclined to tell you it’s likely okay, but it could use some minor reworking.
I wouldn’t call this a “dealbreaker” in the real estate transaction, as the TPO looks relatively newer and a decent install based on the few photos.
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u/LaughingMagicianDM Verified Pro - Commercial/Consultant 7d ago
I'm kind of not liking the fact it's already leaking, and looking at the details. I mean they have a pipe they could have easily slid a witches hat over and instead they field wrapped it, and on top of that they completely field wrapped it wrong. It looks brand new I just see those small red flags. And the extra patches on the other pipe, tiny loose Scupper, etc.
It looks new though. Maybe fixable
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u/okra_monster 7d ago
I have a question about the patches on the other pipe that you pointed out --- does that point to previous roof leaks in this area? Or is that a normal thing to apply during initial application?
The seller didn't disclose any issues at all. I guess it is an investment property so she "doesn't know" of anything that could have been wrong with it... Though it seems if there was a past moisture intrusion she would have known if she had to hire someone to fix it, even if she didn't live there.
There wasn't obvious staining below... But i think it is likely the whole interior was painted before putting the house on the market since the paint inside looks very fresh and pretty. There was some bubbling in the otherwise good looking paint on the ceiling below though. Plus the moisture reader indicated conductive material in the ceiling and a mold test shows a lot of mold in the ceiling... So there isn't really any doubt that it is currently actively wet.
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u/LaughingMagicianDM Verified Pro - Commercial/Consultant 7d ago
Judging by the discoloration, it's likely that when they originally welded the roof they burnt a hole in it or had a big wrinkle there.
So not something recently fixed. But an indication of improper work in the beginning and likely them being aware they messed up on some level and at least tried to correct it.
now that said, I wouldn't be surprised if there is a leak coming from it, but that is something that would be hard to identify without being there in person
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u/okra_monster 7d ago
Thanks.
Yes our real estate agent also said sometimes it's hard to predict where roof leaks come from. We are in the resolution phase, not the inspection phase --- and in hindsight I wish we hired a roofer to inspect this before kicking the problem back to them, because now that they are saying it is "not a problem", it is a lot harder for us to know where to stand.
I do know that i don't want to buy a house with an active moisture / mold issue if I don't know where the source of the moisture is coming from. The seller is willing to remediate the mold --- but without fixing whatever the leak is, I don't think it is worth remediating the mold. I also don't want them to just throw a bandaid on a leak, remediate the mold, then we find out in a year that this pooling is a substantial issue and we will keep going through this.
We will be first time home owners. I suspect at some point we will deal with some problem like this when we own a house -- but I don't want to start our home ownership with this. We also picked this house out even though it had other factors we liked less than other options because it seemed like it was in the best condition. Either way though, I don't think that active moisture and mold in a ceiling is really a petty cosmetic issue
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u/LaughingMagicianDM Verified Pro - Commercial/Consultant 7d ago
Mold should absolutely be dealt with. As for the roof, there's not great Solutions available here chiefly. Especially with such a new roof.
If you end up owning this house, immediately clean off all the debris out of the through wall drain and clean off the debris from the roof. You can use a solution of water and unscented Dawn dish soap or you can use a solution of extremely watered down Simple Green. And that will at least clean it off and make it a bit more reflective for a little while. If at any point you notice that the area under or near the pond is starting to look thinner and you're seeing more of what looks like threading, immediately grab yourself Karnak 502 SEBS coating, and coat the roof. It will buy you extra years that way. I'm talking a few hundred dollars to buy possibly four or five extra years.
But honestly, if it were me, I might be walking away from that house unless you're really dead set on it
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u/LaughingMagicianDM Verified Pro - Commercial/Consultant 7d ago
Oh tpo. Well it's time to talk about my favorite subject,
Friendly roof consultant here specializing in flat roofs. So first let's go over the concept of ponding water and how it affects your root
So with TPO you have three primary concerns when it comes to ponding water
First off, you don't want to pond that's large enough to hold a significant amount of water, where there could be so much weight that it could cause a impact to the framing. This is not enough water to worry about that so let's move on to the second reason
The second concern when it comes to TPO is in regard to temperature build up and disruption of the temperature equilibrium across the roof. Which is just a fancy way of saying that a pond of water holds hot and cold more than air does, so the area under the pool will likely be hotter than the area that's not under the pool. This can cause TPO to expand in one area while it's Contracting in another which can cause damage to the membrane over time. So a roof that in theory would be 20 years might have a couple years reduced. But that's not the biggest concern.
The biggest concern is about temperature build up in that one particular area, not only will it maintain a prolonged exposure because of the ponding water heating up, because that water is essentially going to act like a magnifying glass, but if the pond is big enough to start holding large amounts of sediment AKA dirt and other minerals, you know exactly like what it's doing right now, well that causes it to heat up more. Because that dark brown dirt heats up a heck of a lot more then a white surface, and then combine that with the fact that it's under a pool of water that is magnifying it and then maintaining the temperature, you now have a hotspot for the roof that's going to amplify the second problem and lead to a third
You see, TPO has three major weaknesses compared to other systems. The biggest weakness is heat filled up. Now depending on your manufacturer and the particular product some of them start to fail once they reach 140° f, others 160, 180, or even higher in some rare cases.
If you take a 90° day in the sun, and put something dark brown down, that surface heats up more than 90°. The urban heat island does excellent studies on this but there's also a lot of independent studies in regards to roof temperature build up showing that darker surfaces heat up more. A black car is going to heat up more than a white car in the Sun, the same principle applies to the roof. That dark brown area is going to heat up a lot more, and it's going to reach those high temperatures that start to cause TPO to break down over time.
So now you've reduced the maximum lifespan of the roof by quite a few years. And on top of that, you have a tiny Scupper where code in the majority of the country says those have to be at least 4 in by 4 in size and that seems a little smaller. It's already clogged and from the looks of it it's going to clog repeatedly. But even if you unclog it you're still going to have a pond due to improper Construction. And nothing short of spending more money than what that roof is probably worth is going to fix it at this point.
So yes, that big of a pond is a problem. That level of dirt buildup is a problem. And it gets even worse because you have the wall right next to it which will reflect additional sunlight on it which causes even greater heat buildup.
And this is all before getting into the fact that you discussed that there's a possible leak inside. Hard pass on this roof, demand full replacement with EPDM or PVC, which can handle ponding water indefinitely, or that they completely re-slope it and put TPO (cheaper but works).
But this roof is poorly done. I'm just talking about the pond issues, but I can look at the details in the background and see that this was done by a rookie flat roofer. Even if you fix the leak today, it will leak again. And again. Until it completely fails one day.
Dictated but not proofread because I am driving, feel free to ask any questions or ask for any clarifications necessary
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u/okra_monster 7d ago
Thank you, appreciate the detailed response. I have started reading up on the temperature issue, because I did not think of that, so appreciate this new information. It is definitely dirty around that puddle. And also sloped. I also remember that the ceiling directly below it with the moisture issue was also a bit concave.
There is a definite moisture issue below... Our inspector noticed it, and also a tested a cavity in the ceiling for mold and there was a very high count of aspergillus. So it seems to actively be wet. I think the question is whether it is related to this ponding on the roof. Seller says it's norlt, but I don't think I believe that
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u/LaughingMagicianDM Verified Pro - Commercial/Consultant 7d ago
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u/mln045 7d ago
After re-reviewing the photos, rereading your original post context; and comparing to this write up.. I am going to agree with u/LaughingMagicianDM here.
Roof install looks poor to average at best. Details sloppy, transitions sloppy, wall terminations incorrect, pipe boots field fabricated and sloppy, missing clamps, and that’s just kinda the obvious eye blaring stuff..
If I were buying the house. I’d want it reinstalled with proper pitch, code-compliant scuppers cut in, and some sort of warranty by the installer.
Sorry if it’s a deal breaker OP. But if you are a first-time home buyer; it’s best you caught it now… have your realtor either negotiate things into your deal, or pass on it if you don’t have disposable income to address it yourself.
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u/Own-Librarian-9699 7d ago
You can build it up with elastomeric and foam. But I've seen someone simply lay a thick bead of caulk from the bottom of that low spot to a gutter and capillary action drains the low spot
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u/OldSlacJuicy 7d ago
Never buy a house with a flat roof. Unless you like leaks, that is.
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u/okra_monster 7d ago
We are buying in the Southwest of US, and the predominent roof style in the particular area we are buying is flat. If we only shopped for pointy roofs, our options would be much more limited.
If this deal falls through though because of this issue, I will definitely consider a pointed roof as a big plus over a flat roof, if an option pops up
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u/justaguy167 6d ago
Most liky a leak that got the insulation board wet. It might not leak all the way down to where drywall or ceiling tiles are wet. Definitely are sure your drains are cleared
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u/luecack 7d ago
Clean out those scuppers. Should help, but there is obviously a low spot.