Metal over old roofing shingles

Discussion in 'Roofing and Siding' started by billyjoe63, Mar 26, 2009.

  1. Mar 26, 2009 #1

    billyjoe63

    billyjoe63

    billyjoe63

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    I am going to strip my roof with 1/4's and put metal over the entire roof. I have been told I need something in between for a vapor barrier and have been told I won't need a vapor barrier because of the space from the old roof to the new. I need to know for sure if I need the barrier and what to use. Would roofing felt be okay.
     
  2. Mar 27, 2009 #2

    CraigFL

    CraigFL

    CraigFL

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  3. Mar 28, 2009 #3

    dmackey

    dmackey

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    When warm, moist air comes into contact with the cool underside of the metal roof, condensation will form and drip onto the wood sheathing below. In the Northeastern USA / Eastern Canada, where I install, temperature fluctuations from extremely cold to warm are the norm and metal roofs can sweat to a significant degree. In Texas, it will be less but your money will be well spent in protecting the wood sheathing. I recommend either a 30 # felt (tar paper) or a synthetic underlayment such as Grace Tri-Flex 30 or IKO Roof Top Guard.
     
  4. Mar 31, 2009 #4

    glennjanie

    glennjanie

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    Welcome BillyJoe:
    You are installing this metal roof over old shingles which probably have 15# roofing felt underlayment. That is enough vapor barrier. The space created under the metal along with the corrugations in the metal will allow air flow under the metal; just make sure you leave an exit for the air at the top (or ridge).
    Glenn
     

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