PRODUCT INSTALLATION FEATURE
Understanding Underlayment Installation Here’s how to stay on top of underlayment installation
By Mark Robins, Senior Editor
A roofi ng underlayment is a membrane that prevents water penetration. Com- pared to exterior roof-covering materials like metal or shingles, underlayment is the secondary barrier to moisture penetration. If the roofi ng underlay- ment is installed correctly, water that penetrates the exterior roofi ng materials will drain out to the exterior and away for the building. Without correct installation, water from wind-driven rain or ice dams can severely damage a roof, or even worse, the inside of buildings. The following installation tips can prevent that from happening.
Even before installation Even before underlayment installation, determine if
a permit is required for roof underlayment installa- tion by local building authorities. If one is required, post it on the job site as required. Ensure that the underlayment being used is
compliant with the roof’s specifi cations and applica- tion. Are there special requirements, particularly be- fore installing underlayment on copper or zinc metal roofi ng? Applicators should follow the underlayment manufacturer’s published application guidelines. Verify the delivered underlayment’s model num-
ber, grade, fi nish, size, options and quantity match the order precisely. Thoroughly inspect all underlay- ment materials for damage and proper operation. The size and shape of the roof dictates how
much underlayment material will be needed. “If the geometry of the roof is weird, then you’ll tend to have more scrap,” says Dave Rowe, product development director at Englert Inc., Perth Amboy, N.J. “Find the square footage of the roof for under- layment by measuring the length and width of each
portion of the roof, multiplying length by width for each plane, and adding the planes together for the total square footage. It is also important to under- stand the total number of square feet of material required including end laps and side laps.” The overage/waste should be less than 7.5 percent of calculated expectations. Prepare the area for safe, effi cient work and
move items that restrict work access, or are vulner- able to damage. Cover and protect items that cannot be moved. Avoid roof falls by using safety harness- es, roof jacks and other safety equipment. Mark edges for safety. Always use caution when standing or walking on any underlayment product. “Be aware of safety,” cautions John R. Crookston, foreman at UpRight Inc., Kalamazoo, Mich. “I believe the safety aspect is probably the most ignored.”
Deck preparation For successful underlayment installation, roof deck
preparation is critical. Voids or gaps in the deck need to be fi lled and decking protrusions need to be removed before installing the underlayment. Also, the roof deck surface must be smooth, clean, dry (not damp) and free from contaminants. Wood decking may require a minimum of 24 hours to dry if it is wet. “The surfaces of oriented strand board (OSB),
plywood sheathing and insulation board may con- tain wax, sawdust or other foreign substances,” says David Delcoma, product marketing manager, MFM Building Products Corp., Coshocton, Ohio. “Use an approved primer as necessary to achieve maximum adhesion of the underlayment to the roof deck. Typically, masonry, OSB, aged metal and concrete roof decks must be primed.”
“Membrane adhesion tests should be con-
ducted on questionable substrates to ensure proper adhesion and to determine if approved primer is required for particular substrates,” Rowe says.
Underlayment installation steps In general, all underlayments are installed in the
same manner, starting at the low point of the roof deck and moving upwards, regardless of the material type. “The underlayment’s composition determines the slope, approved fi nal roof covering, installation temperatures and fastening options,” says Delcoma. “For self-adhering underlayments, no fasteners are required. For those underlayments that require mechanical fastening, the manufacturer will specify what type and size of fastener is required.” The following installation steps are provided by
Little Rock, Ark.-based Tarco: • Cut the self-adhering underlayment to suitable, manageable lengths before application.
• Prime all metal fl ashings, leads, eave and rake metal drip edges and vertical approved substrates with ASTM D41 asphalt primer, water-based acrylic primer or water-based polymer modifi ed primer.
• Install fi rst course of underlayment parallel to the eave edge.
• Apply the underlayment working from the center of the material continuously to the ends of the sheet. Half of the length of the sheet is the center. Avoid wrinkles and ridges.
• If one course of material becomes misaligned, do not continue to apply courses as this will lead to wrinkles and fi sh mouths. If any course gets misaligned, start over again.
CLAD-GARD metal underlayment rolls out quickly for easy installation. (Photo courtesy of Firestone Building Products)
A “back-roll” method for installing self-adhering underlay- ments is faster than other methods and helps lay the mem- brane down evenly. (Photo courtesy of W.R. Grace and Co.)
26 METAL CONSTRUCTION NEWS June 2012
MFM Wind & Water Seal high-temperature rated underlay- ment protects this Air Force base metal roof in Ohio. (Photo courtesy of MFM Building Products Corp.)
www.metalconstructionnews.com
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