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Q&A: What is a remedy for our leaky flat roof?

Modernhome2Question: We own an apartment building in North Hollywood that has a totally flat roof. Every few years we install a new composition roof and it starts to leak again. We believe that the solution lies in providing a pitched roof. Would you know of any companies that could install a totally new inclined roof. We sure could use your help. — Karl

Answer: Karl, I spoke with two licensed general contractors with decades of experience each and their consensus was that putting a sloped roof on top of your building would be many, many times more expensive than paying top dollar to get a superior job done to your existing roof.

The advances in roofing technology are amazing. Have you seen mention of “green roofs” lately? These are flat roofs covered with a thick rubber membrane that allows for turf to be planted on top. This is done for insulation value, to cool off the building in hot climates and to provide oxygen to the air. You could take advantage of these new materials to get a better roof than composition material could provide.

I asked Chatsworth general contractor Alon Toker of Mega Builders what he thought about creating a sloped roof over a flat roof, and here’s what he said:

The reframing option would require expensive plans and engineering, and then the framing and roofing. But compared with a quality reroofing of your current roof, the reframing option would be several times more costly. Continued . . .

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The problem with flat roofs is water runoff can be poor. Also, the sun (the real enemy of roofs) hits the roof at close to a true angle, and so it is most destructive.

The bottom line is that flat roofs are more susceptible to leaks, so shortcomings in materials, installation or both have more consequences.

If a reroof is done to the highest quality possible, a building owner should get more than 10 years from a flat roof (12 to 15 is a reasonable expectancy). Not many roofs (flat or pitched), however, are done to the highest standards, unfortunately, and given its greater susceptibility, the flat roof will show its faults sooner.

The remedy is not reframing of the roof (an investment never to be recaptured) but educating yourself about flat roofs and limiting the bidding to top roofers. You want the best company using the best materials available. In challenging home-improvement situations, it always does seem to get around to this, doesn’t it? In the long run, though, you will save money and hassle with a superior flat roof, and I think that is your goal.

4 Comments on Q&A: What is a remedy for our leaky flat roof?

  1. the rubber membrane that is supposedly the best is called “EPDM” and is on 35% of commercial low-slope roofs already. the white versions are Energy Star rated, so will qualify for part of the chintzy $500 rebate program. the adhesive version (as opposed to the rock-weighted or metal-clip-down versions) is said to be best, but MUST be installed by a certified installer. amateurs will not be able to fake it. i LOVE flat roofs and have been researching this a lot for my desert place. the energy star roofing section has a list of manufacturers and qualifying products…
    foam is supposed to be great for the type of roof that has a (warning: totally non-technical term coming up) “rim” around it, but is harder on just a basic rooftop, because from what i understand, you will have to build a frame to hold it in.
    good luck!

  2. I agree with the contractors. Reframing, re-engineering, and permitting (on a possibly older building) could be a complete nightmare and cause far more in money and time than doing a top quality roofing job.
    Flat roofs aren’t the problem (almost every commercial buildling in LA has a “flat roof”). It’s the roof membrane. I bet the “composition roof” getting put on periodically is a P.O.S. old-school built-up-roof.
    If you want a nearly completely bulletproof system, try a hot-rubberized roofing system. It’s basically the same thing as the “green roof” mentioned in the post, but there is no planting or turf. It’s just the waterproofing, with some additional coverage to protect the membrane from U.V. light. This stuff will work on a dead flat surface. It’s expensive, but you’ll only do it once.

  3. Thanks, M, for your wise comment. I wanted to clarify that I wasn’t suggesting a green roof for Karl, just suggesting there are a lot of technologically advanced products on the market. It’s good to hear about the one you suggested, and I love the idea that it provides insulation!

  4. RE: roofs
    Green roofs need to support a lot of weight, like a roof deck would need to. structural changes. not a simple solution and during a heavier rain there will still be runoff. In contrast check out foam roofs, they work well on flat roofs and have a high insulation value. It sprays on and can be made thicker or thinner to provide slope that’s not visible from ground so you can direct water away from low points. Can be 1.5x to 2x price of a composite torch-down roof but then you get the great insulation and lasts. however it can’t be walked on.

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