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Question DetailsAsked on 2/3/2017

roofer near 39422

Part of the of the addition had to be flat roof to tie on to existing roof . Approx. 10 x12 feet has started to leak .
Thanks Jimmy Evans

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2 Answers


Sorry to say this, but this is all to common a problem - generally because the designer did not take enough trouble to anticipate roof interface problems. Normally, this would be properly handled by putting in design in a transverse ridgeline - running the ridge perpendicular to the main roof ridge, so the water from the addition spills off both "sides" and the water coming down the main roof to it is diverted to each side by the new transverse roof - like this photo, where the framing-only the part sticking out toward the right is the addition.

That can be with a full peaked roof, or a three-sided gabled roof.

Another common solution is to "back up" the roof onto the existing roof and give a general flatter but proper draining slope to the entire roof section with a shed roof extension, like below - - how far up the roof you have to go to the intersection point depends on drainage and ice damming considerations - (the gabled roof with shed roof addition one) and relative elevations and how far out the new extension reaches - pretty easy usually with porches,, but the further the addition stretches out from the wall of the house the more difficult it gets to do with a shed type (unpeaked) roof.

You can also reslope the upper existing roof back the other way - off the "back" side, commonly done in modern design homes, or use a sloping shed roof on the addition but lower the addition (and commonly surrounding ground level too) if topography suits, so the addition sits lower and its roof can either continue off the existing one at the same slope, or generally better - start a bit lower than the existing roof and then slope out like this -

Of course, building the extension off the gabled end of the house also works, as that pretty much totally avoids roof interface problems - at least with one-story additions off a 2 story house.


Now to your existing problem - this is very common - generally best to bring a flat roof, if you have one or have to have one, like that in under the sloping roof with some clearance (to prevent damming from snow) without actually tying the two roofs physically together, other than maybe with a splash/blow-in guard vertically between them. If the sloping roof runs down "onto" the flat roof, then a full waterproof membrane needs to come from the upper roof (under the normal tarpaper or water barrier) down onto the lower roof - sometimes best running all the way over the addition as the roofing membrane there too, in a seamless water barrier. Basically, the "flat roof" needs to use a synthetic membrane (generally not good to do this with tar built-up roofing) to run up under the house roof to provide continuity if they cannot have a physical break in elevation between them like this, though the elevation break does not need to be this pronounced unless you are trying to save windows like they were.

Course, depending on where the lesk is - this might be an intersection leak where the sloping roof meets the flat roof, or just a failure of the flat roof (how I hate flat roofs, especially on residences where there is generally no excuse for them).

Clearly you need a Roofer (your Search the List category) - and assuming the addition roof is insulated or lies on plywood sheathing, I would recommend one who has a thermal infrared camera so he can detect the leak saturated area and hopefully tie down the source area.

Answered 3 years ago by LCD



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