Guest User
2/21/2009
Are there any experts that can answer the question I asked about Metal Roofing Installation as a radiant barrier. Question was posted a week ago, but no replies yet.
Guest User
2/21/2009
Its difficult to understand exactly what you are asking. If you use metal roofing that is an energy star partner (cool technology) than you get a better solar reflectance from the steel it self. Even black from some manufacturers. You can put low e reflective insulation on wich is a vapor barrier also. It carries a R value from 8.1 to 13 depending how it is installed. As far as the diagnal purlins I dont think thats needed. If you have proper insulation and ventilation you shouldnt have moisture. Yes 1x4 is fine you actually only need 5/8" to meet most manufacturers specs.
Todd Miller
Classic Products, Inc.
2/21/2009
I agree that diagonal purlins are probably going to cause more troubles than worth. A radiant barrier is good but it needs to face an airspace, not be part of a tight sandwich of materials.
Guest User
2/21/2009
The purpose of the battens (purlins) is to provide air space between the underside of metal roofing and top of moisture barrier covered roof decking. The purpose of the roof decking is not only as a substrate upon which to support the moisture barrier, but also to provide a structural diaphram across the roof plane, transferring design wind load (140mph) to load-bearing exterior walls. Condensation occurs when moist air (humidity) meets cold surfaces. The air space created under purlins will cause condensation at the underside of the metal, hence the purpose of the sloped purlins - to fascilitate drainage of the condensation. This may complicate installation for some, but makes sense in climates like the Gulf Coast. The question that i would like answered is: Can anyone direct me to any Rib Panel Manufacturers Installation Instructions that specifically address the installation of 1x4 #2 S.Y.P. battens (purlins) installed over 7/16 O.S.B. roof decking. Instructions abound for installation on 2x4 purlins OR 5/8" CDX Plywood, but for the construction of an affordable LEED Certified home, it is our intention to reduce cost and the use of resources while acheiving the the structural integrity required for 140mph desidn wind velocity.
Guest User
2/22/2009
I have only seen the recomendation of 5/8" solid substrate. I dont believe you will find a manufacturer to show examples of diaganal purlins. I think your are over thinkinking a bit, if you have proper ventilation your roof system should always be very close to the outside temp. Using steel with transfer the temp quicker than shingles. Also if it is cold outside and you have a properly insulated/ventilated house the heat that escapes your living space will be cool very quickly therefore never creating condensation.
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