sequence of roofing materials, for flat roof?

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Old 07-21-13, 01:59 AM
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sequence of roofing materials, for flat roof?

I'm a newbie, working on a shoe-string to gut and salvage the small 1950s house I inherited, but with no cash to "do it right." It is either make-do, or lose the house. It will be torn down whenever it is sold, and a McMansion built.

I have a question on recommended roofing materials for the flat roof, and their sequence. The roof is flat and is 32 squares (including shop and carport), in the rainy Pacific Northwest. Does the following sequence make sense? Or is the sequence wrong? Can I cut anything, to save money? Anything I should add, like Tyvek/Typar -- if so, where?? From the top down:

* membrane (probably PVC; or torchdown)
* #30 roofing felt
* peel-stick water-and-ice barrier [GAF or Grace or ??]
* [possibly 1" XPS rigid foam insulation if I can afford it, to insulate and smooth any rough old deck; R5]
* old tongue-and-groove wood decking (on drip-edge replaced 4' in, and as needed)
* 2" airspace
* 5.5" Roxul rock-wool insulation R22 [more mold-resistant than fiberglass]
* drywall ceiling (probably paperless-drywall, to limit mold; DensArmor or ??)
* latex paint (Kilz II primer)

It's a very flat roof, a 1:16 slope (too flat) that leaked on and off for years, so there was a very serious mold problem (requiring a complete gut inside of all drywall and trim). I need to tear off layers of old build-up (hot-tar) roofing, and repair parts of the deck, and fix some joists/rafters that are rotted for 3' on the drip-edge. I've read lots of debates about torchdown vs PVC membrane. I'm currently leaning towards PVC, despite the higher cost, as its safer for me to install myself (no flame), and white is better in summer (I've no A/C). I worry about condensation if I use PVC, though I'll add at least two 2-way vents (kitchen and bath) and the soffits have vents.

I really appreciate any sound advice, especially from those who've been around long enough to see fads come-and-go. Many thanks in advance!
 
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Old 07-23-13, 09:00 AM
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Any suggestions are welcomed. Thanks!
 
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Old 07-23-13, 11:34 AM
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I'd skip the Kilz and use a regular low VOC primer.
drywall
5.5" Roxul
2" airspace
old tongue-and-groove wood decking Securely nailed
rigid foam insulation
PVC

Other options include liquid roofing (Hydro-Stop) and metal roofing.
 
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Old 07-30-13, 12:23 PM
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Thanks, Dan!

I'll look up Hydro-Stop, new to me, thank you.

Just to clarify, are you saying I can get away without using either ice-and-water barrier or roofing-felt? (Given my dire financial circumstances, and that the house will for sure be torn down whenever sold, probably within 10 years.)

I worry about condensation under the PVC rotting the roof deck.

Thanks again!
 
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Old 07-31-13, 07:28 PM
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The PVC should not come into contact with petroleum products (felt paper, peal and seal sticky side, asphalt products). There shouldn't be condensation problems but you could install vents in the roof just in case.
 
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