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Old 10-22-2008, 03:58 PM   #1
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Old Flat Roof


Sort of a long story here:
Saw overflowing from my eavestroughs and went up at the back of my house to look at them. Realized the problem was due to sagging because the fascia board was rotten. Looked a little further and saw the flat roof (1 in 48) membrane had come loose around the edges. As a result, everything under the membrane was soaking wet. The roof deck is made from 10 - 12" wide cedar planks 1" thick covered in tar and paper layers plus gravel layer after layer. As best I can check, the boards are good, but the build up layers including cover up fiber boards are all soaking wet. I'm guessing all the wet stuff has to come off. I'm thinking of placing rigid board insulation on top of that when its done and then using a two ply membrane over the insulation board. Does this make sense? The house was built in the 1920's and the flat roof has no provision for venting.

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Old 10-22-2008, 07:54 PM   #2
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Old Flat Roof


It does need to all come off. Venting on a flat roof is still required by code on the per square foot model, but actually is very inefficient for drying out any of the roof decking or insulation once it becomes wet somehow.

You need to know the exact square feet of that section and inform us, so that you can vent the attic section underneath as best as possible.

Venting options on flat roofs are much slimmer than for steep sloped roofs.

Ed

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Old 10-22-2008, 10:44 PM   #3
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Old Flat Roof


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Originally Posted by Ed the Roofer View Post
It does need to all come off. Venting on a flat roof is still required by code on the per square foot model, but actually is very inefficient for drying out any of the roof decking or insulation once it becomes wet somehow.

You need to know the exact square feet of that section and inform us, so that you can vent the attic section underneath as best as possible.

Venting options on flat roofs are much slimmer than for steep sloped roofs.

Ed
The area of that part of the roof is 18 x 30 and it finishes by running up onto the sloped roof (shingled) at the front of the house.

When you say "need to all come off", do you mean down to the first stable dry layer or all the way down including the deck? There is no possibilty of venting at the rear of the house as the roof deck boards actually touch the brick wall. Even if I opened that for inlet, where would the exhaust go?

Had a roofer look at it on the weekend. He suggested taking off the existing felt, taking away the wet stuff underneath that, putting down a vapour barrier, and 2" of polyiso (R-14) on top of that finsihed with two ply torch-on modified bitumen with granulated surface.

Last edited by diyjim; 10-27-2008 at 10:56 AM. Reason: More info
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