The Waltham, MA-based Single Ply Roofing Industry (SPRI) offers the following answers to frequently asked questions about sheet membrane roofing.
Q: How do I maintain a single-ply roof?
A: All low-slope roofs should be inspected at least twice per year, and after a major storm. Look at the perimeters for loose metal or fasteners; the roof should not have loose membrane or fasteners that form tents. Pay particular attention to flashings around penetrations. Make sure they're tight and undamaged. Remove debris and ensure that all drains are open. Note any changes from the last inspection; if questions arise, consult a registered roof consultant or the contractor who installed the roof.
Q: What wind ratings are available for sheet membranes?
A: Sheet membranes are rated in pounds per square foot of uplift resistance. Factory Mutual is one of the widely recognized agencies that measures uplift pressure. Factory Mutual uplift pressures are reported from 60 pounds per square foot to 999 pounds per square foot uplift resistance (FM 1-60 to FM 1-999), and SPRI members offer systems that meet that full range. See Exposure Categories and Zonesto help determine the exposure category of exposure zone (wind) for a building.
Q: Can I reuse existing roof insulation when recovering/reroofing?
A: The reuse or recover of building products, including insulation, is typically an economic choice. Recent technology advances and product developments will not be present in previously installed products. The owner/owner's representative must compare these product enhancements to the economic advantages of reusing or recovering existing products. Individual manufacturers should be consulted regarding specific criteria for reuse and recover of existing building products.
Insulation loses very little R-value after the first 5 years; therefore, older dry insulation is likely to maintain a significant portion of its original R-value. SPRI research shows that damp insulation can dry to the interior of buildings if there are no barriers between the insulation and the building. (Typically, wet roofs on metal decks with no vapor barrier will dry, whereas insulation over concrete decks has no opportunity to dry to the interior.) Before recovering over existing insulation, it's advisable to make core cuts to determine the characteristics of the existing system, primarily to determine if there is a vapor barrier in the system that would prevent drying. It's advisable to conduct moisture surveys to determine if wet insulation exists and where it's located. Most roofs will not be entirely wet. The wet insulation can be removed from areas where the system will not be able to dry and replaced with new insulation. Again, consult the individual manufacturer regarding specific criteria for reuse and recover of existing building products.
Q: How long will sheet membrane roofs last?
A: Due to the variety of conditions and circumstances that exist, no guarantee of length of life of any roofing product can be made. But, quality roof membranes, properly installed and maintained, are still performing today.
The Single Ply Roofing Industry (SPRI) offers a number of standards, technical reports, and publications that can be downloaded or purchased on its website.