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JohnCO 
Orange Level
Joined: 11 Sep 2009
Location: Niwot Colo
Points: 8992
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 Topic: Underlayment for metal roof
Posted: 03 May 2019 at 12:31pm |
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My rental house roof is leaking and I've decided to remove the asphalt shingles and replace them with pro panel steel. I have to replace some of the plywood under the roof as it has started to rot. Wondering what you all think I should use for underlayment. Seems like tar paper isn't in favor anymore as it doesn't seal to the wood well. TIA
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jaybmiller
Orange Level Access
Joined: 12 Sep 2009
Location: Greensville,Ont
Points: 24780
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Posted: 03 May 2019 at 12:54pm |
The Hy-Grade steel roof on my house has been on 12-14 years ? Install consists of strapping 2by3 vertically over existing roof( it was slid), then strapping 1x4 horizontally, then the steel shingles go on that. It provides a solid WELL ventilated underside for the steel. LOTS of air flow is necessary.
In your case, Once the mess is removed and repaird , I'd cover 100% of the roof with 'ice and water shield' or whatever it's called south of the 49th. The low pitch(3-12) addition was 100% covered then we put 3-4 layers of it at the 'valleys',each one bigger than the last by 2-4 inches.Not one drop has ever come into my house since then. I don't know what 'pro panel steel' recommends for air gap, but I'd suggest 2by4 vertically instead of 1x3s. Cost is not much more and 2by4 are better boards. Buy 16' one, better grade, at least up here, so less waste.
Jay
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Dakota Dave
Orange Level
Joined: 12 Sep 2009
Location: ND
Points: 3972
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Posted: 03 May 2019 at 12:54pm |
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Up here we use ice shield on top of the decking and steel directly on top of that. that is current code for new residential construction.
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DMiller
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Joined: 14 Sep 2009
Location: Hermann, Mo
Points: 34403
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Posted: 03 May 2019 at 3:49pm |
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What the installer was told here(no code) was 3/4" underlayment for steel or furring strips 1x3 or 1x4 at no greater than 32" intervals, Use a decent top cover on the plywood prior to the furring strip install. We have a sheet material called titanium paper under our roof.
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Thad in AR.
Orange Level Access
Joined: 12 Sep 2009
Location: Arkansas
Points: 9668
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Posted: 03 May 2019 at 5:05pm |
 DMiller wrote:
What the installer was told here(no code) was 3/4" underlayment for steel or furring strips 1x3 or 1x4 at no greater than 32" intervals, Use a decent top cover on the plywood prior to the furring strip install. We have a sheet material called titanium paper under our roof. |
Titanium paper and similar is what they put under everything around here. I like it because if it gets rained on it doesn’t wrinkle up.
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Stan IL&TN
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Joined: 13 Sep 2009
Location: Elvis Land
Points: 6730
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Posted: 03 May 2019 at 7:44pm |
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On my 2/12 pitch I have ice and water shield on top of deck then the steel on top of that. Been on maybe 15 years and no leaks.
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1957 WD45 dad's first AC
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shameless dude
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Joined: 10 Apr 2017
Location: east NE
Points: 13607
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Posted: 03 May 2019 at 9:31pm |
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hot tar it! lol
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Dakota Dave
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Joined: 12 Sep 2009
Location: ND
Points: 3972
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Posted: 03 May 2019 at 10:53pm |
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If you put the ice shield on the deck and steel directly on it youll have a very quiet roof.with a continous ridge vent you wont have condensation problems.
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