Leaking flat roof on relatively new house in NM => pvc membrane roof?

June 29, 2013 12:29 PM

Our house is a six year old flat roofed house in New Mexico. Every time it rains or snows, the roof leaks in several places. We've gone up there with tar and sealant about 5 times in 18 months. Sometimes we fix it, but not before another leak forms elsewhere. We invited several membrane type roof vendors over for estimates and they range from $20K-$26K for a roof with a lifetime guarantee. The membrane roofing seems like a good idea. Does anyone have experience or advice with finding a permanent solution to a leaking flat roof.
posted by alcahofa to Home & Garden (9 answers total)

Is there anything on the roof besides the room itself? That is, is there an ac unit or something that would have to be reattached to the roof after the membrane was put on? Anytime you put a hole in the membrane, you are risking a leak point. No holes, works real well on the commercial building I know about. The only thing that worked as a solution to the leaking on this commercial property was when a membrane type roof was installed.
posted by JohnnyGunn at 1:04 PM on June 29, 2013

I'd tend toward repairing the roof that you have, rather than replacing it.
6 years is not nearly end of life for any roof.

I'm not a pro, but I've fixed numerous leaks that were installed by the original builder of my house (flashing failures), installed skylights that don't leak, and had to threaten a roofer with lawyers to get them to fix leaks. I've lived in NM in flat-roofed, swamp cooled houses.

When you say, "another leak forms elsewhere?" what do you mean?
Do you mean that another place inside the house gets wet?

If so, then you might not be fixing leaks at all. Water from roof leaks can often migrate"horizontally" some distance from where it gets through the roof. There is often no correspondence between where you see water on the drywall/stucco and where the water is coming in.

You probably don't have an "attic", right? It's a latticework of engineered wood I-beams with insulation, which is a hellish place to try to find a leak. You might have even less, which would be just an insulated roof deck.

Take a water sprinker on the roof, and test your roof in small sections, say 8x8 feet. That can help you localize the leak locations. Be systematic and patient.

Are there any puddles anywhere on your roof when it rains? If so, these are sites that should be eyed suspiciously for breaks and leaks.
posted by the Real Dan at 1:15 PM on June 29, 2013 [1 favorite]

We had pretty good luck with a sprayed foam flat roof, but it was not a lot cheaper than membrane. It was also the 2nd application of sprayed foam, the first time around was not well done and leaked horribly. We felt it was the best way to deal with various parapets/swamp cooler/roofline issues and avoid a tearoff. In our current house, we called a roofing repair company repeatedly until the leaking finally stopped. It's held up for 3+ years fine after about a year of persistent patching. We've been advised that membrane is the real fix but we've chosen to pursue other repairs first (would need almost 4k sq ft!), as the patches seem to be holding. In asking around, what seems to be "normal" among people who will never pull together 10-30k at one time for foam or membrane is to reroof cheaply with tar/gravel every 5-10 years.

Also, our current house does not have parapets but has a metal flashing around the edge. We were getting a significant leak in the middle of our ceiling that was actually caused by the edge flashing coming loose in the wind, about 15 ft away. Once we found a roofing guy that figured out that was the problem, he secured the flashing and the leaks stopped. The first place we worked with was obsessing over a patch in a different spot and kind of threw their hands up in the air and gave us a quote for a tearoff/reroof in that section. I think in NM specifically, a lot of roofing companies make their money off of repeated tar/gravel reroofs as described above and aren't that interested in solving the problem past the immediate leak.
posted by pekala at 1:23 PM on June 29, 2013

While fixing leaks every 3 months isn't anyone's ideal, there really is no "permanent" solution to a leaking roof, just because every type of roof has a lifespan. It's also not necessarily the case that the roof material that's up there now is actually the problem.

"Flat" roofs should actually have some slope to them - usually a minimum of 1/4" fall per foot of run. If your roof has less than that at any point, or if your drains/scuppers are blocked, water will pond on your roof and there's nothing any roof material will do to stop it from leaking eventually. If your existing roof was installed incorrectly, installing a new roof may fix the problem, but it won't have anything to do with the roofing material.

As JohnnyGunn indicates, the roof design and layout may come into play. If there are penetrations (as in, ones that are meant to be there like flues and vent pipes), those can be leak sources more frequently than the roof field, just because trying to install the roof around the penetrations can be difficult and the solution is never totally ideal. Similarly, if there's a wall interrupting the roof and the flashing at the base of it has gone bad, changing the roof material won't really solve that problem.

Anyway, I haven't worked with PVC, but I have worked on a few projects (in an architectural office) that used TPO, which has some of the same properties (white single-membrane that's able to be heat-welded). TPO warranties generally run 15-25 years depending on the type of installation and types of penetration details needed. The drawback to single-membranes is that once it's punctured, there's no backup like there is with a 3- or 5-layer built up asphalt roof. However, fixing a puncture is really easy - you just get a piece of roofing and heat weld it over the hole. However again, you probably won't be able to do this and you'll need to hire somebody. Other benefits are that companies manufacture flashing pieces with TPO or PVC attached to them already, so all you need to do to seal it is heat-weld the membrane on.

So, the first thing is to remember what you've seen in the past - if there's water collecting on the roof during/after rain or snow, your problem is not your roofing material.
posted by LionIndex at 1:31 PM on June 29, 2013

I would start with the advice here regarding the water collecting. Then I would invest in some buckets of that white roof "paint" stuff that dries very rubbery. A couple of good coats of that should work as well as a membrane. Just not for as long.

Also, a roof that young ought to have some kind of warranty from the original installer?
posted by gjc at 2:44 PM on June 29, 2013

Best answer: Seconding the sprayed foam roof. We have a 50-year-old, flat-roofed Stamm house in Santa Fe. Our roofers tore off 3 previous tar-and-gravel applications (including the ORIGINAL pumice gravel) before foaming. In addition to sealing the roof completely, it also insulates. We've had it for 5 years without problems (knock wood), and have really noticed a difference in the heating/cooling.

Many many houses in our neighborhood have had sprayed foam roofs put in (on?), and we were able to ask around about vendors/pricing/people's opinions/experiences. Assuming your neighborhood was all built around the same time, have any of your neighbors had the same leaks? Or can recommend a solution/vendor that worked for them?

Also, yeah, $20K for a whole new roof is not out of line. Sorry.
posted by mon-ma-tron at 6:05 PM on June 29, 2013

Concrete roofing on a flat roof, the contractor stapled down steel mesh and then trowled an acrilic concrete roofing mixture on, it has been worry free for years . the link is a DIY method.
posted by hortense at 6:59 PM on June 29, 2013

Have you checked if your roof has a warranty? 6 years is very short for multiple leaks.
posted by gnutron at 7:58 PM on June 29, 2013

I wonder if your "repairs" are part of the problem. PVC is not compatible with asphalt products like tar. Here is some more. Plasticizers in the PVC migrate to the asphalt and the PVC becomes brittle, more likely to crack and leak.
posted by Crankatator at 7:29 AM on June 30, 2013