Guest User
7/21/2004
Sirs, I am very confused about proper technique of installing metal roof to prevent condensation problems. I have heard from different installers the following: 1. Place sheathing on top of trusses with no vapor barrier under the roofing like felt etc. But make sure there is adequate high and low ventilation. 2. Do the same thing but make sure there is a vapor barrier under the roofing like felt, tar paper. 3. use stripping approx 1 foot apart on top of trusses with or without felt vapor barrier. Please give me your suggestions as far as sheathing or strips, vapor barrier under metal roof, insulation below roofing, ventilation methods necessary for trussed attics and cathedral ceilings. Thanks for your expertise and suggestions. John H
Guest User
7/22/2004
The #2 and #3 options above are both feasible, based upon what style of product you choose to install. The first option -- installing over decking with no underlayment -- should never be done. Proper ventilation requires intake (typically soffit vents) and exhaust (typically ridge vents) with an airspace of at least 1" to carry the air. Once you find some metal roofs you like, the individual manufacturers can help you determine best application methods for your home.
Guest User
8/1/2004
Not clear and need more details for my situation: Installing new metal roof and the existing roof has 2” X 6” rafters & ceiling joists trusses every 2’ on center, 1” X 6” tong and grove roof sheathing, roof felt, and 4 layers of asphalt shingles. Was built in 1942 by the US Government (Army). Willing to remove down to the 1 X 6” roof sheathing and build back to protect and control condensation. Please give me a good design to build back under a new 29 gauge metal roof. Do I need to include spacers between roof sheathing and metal for ventilation? Existing attic ventilation incorporates two open end gables facing East and West allowing cross flow. The top ridge is closed and so is the soffit closed. No up draft ventilation only have cross flow ventilation but seem sufficient.
Guest User
8/6/2004
We are having metal roof installed over a tar paper/tarred, nearly flat roof over our garage. Should we put metal mesh down before installing the roofing material to give adequate ventilation?
Guest User
8/6/2004
Hi Barbara. Several things. 1) You say "nearly flat." Many metal roofs should not be installed on roofs of less than 3:12 or sometimes 2:12 pitch. Do you know that the product you're installing is appropriate for your roof? 2) I am not sure what you mean by "metal mesh" but I assume your mean vertical and horizontal battens which could be ventilated. Not all metal roof products are appropriate for installation over battens. You'd need to check into that first. 3) Are you installing only over the garage or over the house as well? 4) Do the garage and other areas being roofed have a conventional attic space inside or is the construction different than that? If you have an attic space which can be vented, that would be best. If there is not attic, then the idea of battens, with an appropriate metal roof, is not bad.
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