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Old 04-27-2012, 03:00 PM   #16
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Cold Deck flat roof and insulation question...


Depressing--another year and this roof is still not done. And now it is leaking.

First estimator was out this week--he thought strip the asphalt/gravel, and use insulation on top, then an EPDM sheet. Waiting on the estimate for details.

My question--since the deck was built as a cold deck (see illustration)--that puts the insulation above the air flow provided by the continuous venting at the eaves. So insulation on top doesn't do much.

When I asked him about this, his suggestion was just to block all the eve venting (they are those long continuous strips). In answer to Grumpy's comment above, they ventilate all the rafter bays.

And he more or less said that stripping the whole roof would be a lot of work and not necessary since the roof seemed sound.

My worry about using ISO board on top is also that you would need a fair bit for a decent R value, and then you would change the look of the fascia, which is just a turn-up gravel stop level with the BUR--and I don't think you will gain a whole lot when the roof is stripped/

Should I look for someone else?
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Last edited by paredown; 04-27-2012 at 03:14 PM. Reason: Detail
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Old 05-15-2012, 05:11 PM   #17
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Cold Deck flat roof and insulation question...


Second roofer was out today. I've got a temporary patch on the leak that seems to be working, so the panic is subsiding a little.

Second roofer is also not interested in stripping the sheathing off the old roof--says that the rafters are likely to move, and damage the ceilings below anyways. This was a new idea to me--anyone care to comment?

His preferred material is epdm--so the procedure would be to clean the moss, etc off the roof, put three layers of 1" (ISO?) roof board on top, tapered to create a slope. When I asked him about the problem that creates, of putting insulation on top of the existing venting, he at first suggested blocking the existing soffit vents, but then thought that might be a problem since there is some insulation in the ceiling (foil faced) so you would have two vapor barriers.

So he will give me two prices--one with the minimum ISO board needed to create a slope, a second price for adding the 3 inches.

This paper suggests two ways to create a closed flat roof with insulation--basically board on top as the roofer suggests, or spray foam from inside to seal, and then packed insulation in the rest of the joist cavity. In both cases they assume no venting.

So I guess my question is--am I crazy to think that deck off, insulate from the top using fiberglass (and add blocking at the ends of the insulation to prevent excess airflow through it), preserve the profile and clod deck that is there (and the ceilings inside) is crazy?

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