Guest User
4/24/2004
With the summer building season nearing I'm planning on building a new garage with a metal roof. I do not want the dang thing to drip a drop of condensation inside my garage. What should I do to prevent this? Some pertinent details: 1. Constructing in Washington state 2. 8/12 pitch 3. Radiant heat 4. Insulation between the rafters My game plan now is to attach OSB sheathing to the rafters, then a barrier on top of the OSB, such as standard roofing felt, then 2 x 4 purlins, and walla...the metal roof screwed to the purlins. Will this construction procedure prevent condensation in the garage for the life of the roof? I found a similar thread on this site where Allan Reid recommended using Tri-Flex 30 or Micro-E barrier. As far as vapor barriers go, is this stuff really superior to regular old roofing felt given the above construction parameters?
Todd Miller
Classic Products, Inc.
4/24/2004
Jarvis, Condensation occurs when warm moist air strikes a cool surface. In this case, first of all, I am not sure if warm moist air will be present in the garage. Assuming the garage is not heated and there will not be some other source of warm moist air getting into it, the construction you have described should be fine. Ideally, though, I would suggest soffit vents and a ridge vent in the roof, particularly if there may be some sort of source of moisture into the garage. It sounds like your garage will be relatively "unfinished" at least in regards to not having a ceiling? (If it does have a ceiling and attic space, then I definitely would go ahead and use soffit and ridge vent.) Speaking from personal experience, my crawlspace access opens into my garage and I have had some problems with dampness in the crawlspace. One night when it got very cool outside, I accidentally left the crawlspace access open but I closed my garage door. The next morning, I did have some condensation on the walls of my finished garage. Regarding underlayment ... first of all, I would check with the roofing manufacturer and use an underlayment which they suggest. The newer polymer underlayments are more durable but a primary benefit of that is during the installation process, before the roofing is fully installed. I hope this helps. Do not hesitate to post additional questions.
Todd Miller
Classic Products, Inc.
4/24/2004
Jarvis, One other thing I could have mentioned would be to use insulation which has a vapor barrier on the inside and then tape the seams between the batts. This would also help in keeping warm moist air away from any cool spots.
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