• Remove the split release fi lm following a proven technique, or by folding the membrane over and removing one half of the split release fi lm. Then fold the membrane back into place one side at a time.


• The split release fi lm should be removed in a continuous fashion one side at a time. Roll or broom the entire membrane surface, paying special attention to all overlap areas (side laps, end laps, T-Joints) to ensure adhesion with acceptable substrates.


• Allow for all end laps to be a minimum of 6 inches and head/side laps to be a minimum of 3 inches.


• Stagger all end laps a minimum of 36 inches from the preceding course on low slopes (<2:12 pitch) and a minimum of 18 inches from the preceding course on steep slopes (>2:12 pitch).


• Back nail the membrane on steep slopes (>2:12 pitch) or per applicable building code.


• Use a minimum of a 70-pound weighted roller for low slope (<2:12 pitch) and a minimum of a 28-pound weighted roller for steep slopes (>2:12 pitch).


• The use of a soft bristled push broom may be used on steeper slopes.


• Apply SBS trowel-grade modifi ed asphalt adhesive/fl ashing cement in between all granule-over-granule and fabric-over-fabric laps.


• Apply the SBS trowel grade modifi ed asphalt adhesive/fl ashing cement at a rate of 1/8-inch thick throughout the minimum 6-inch end lap contact area.


• Once this procedure has been completed, the underlayment must then be hand rolled in place in order to ensure contact of the underlayment to itself and achieve a minimum of 1/8-inch asphaltic bleed out in the designated area.


• Certain underlayments will adhere to themselves therefore not requiring the use of the SBS trowel


grade modifi ed asphalt adhesive/fl ashing cement in between the 6-inch end lap contact area.


Eaves, corners and valleys Installing underlayment on a roof’s special fea-


tures, like eaves, corners and valleys, requires special instructions. “Normally, we will install a self-adhered underlayment on the bottom eave and in the valleys,” Crookston says. “We will carry it up the walls several inches to seal it. This self-adhered underlayment should be carried up at least 2 feet inside the outside wall for ice buildup. We install the valleys fi rst, and then install the lower sheets starting at the eave and working up. If you install the bottom sheets fi rst and then install the valley sheet over the top of them, it will leak.” A fi nal step in underlayment installation is


metal fl ashing. To reinforce roof valleys and edges, fl ashing provides extra strength and barrier proper- ties. Edges are the most susceptible to water damage and need more protection. Water collects in valleys, thus additional water sealant is needed. These specialized areas of fl ashing require a mini- mum of 6-inch underlayment overlap to accom- modate and withstand the structural movement common around them.


Underlayment installation mistakes Ignorance is a common cause of underlayment


installation mistakes. “The most common mistake contractors make when installing roof underlay- ments is that they have not made themselves familiar with the underlayment manufacturers’ approved substrates or published application guidelines,” says Steve Ratcliff, president and CEO of Tarco. “This can be easily overcome by either contacting the underlayment manufacturer directly, or visiting their website and researching the under- layment application guidelines.” Ironically, a common mistake in underlayment installation is to rely too heavily on the underlay-


ment for the roof’s waterproofi ng. “On a fl atter- pitched roof, the doubling of the felts gave some added protection with shingles, but we installed thousands of roofs in the 1950s, 1960s and 1970s with no felt at all,” Crookston says. “If a roof has to sit exposed to the elements, a good underlay- ment installation will keep the building dry until the roof is installed. If a person could install the shingles and then jerk the underlayment out from beneath them and the roof was correctly installed, there would be no leaks. However, most roofers today rely on the self-adhered membranes for the waterproofi ng and they just throw the shingles on. Eventually, it will come back to bite them.” To learn more about correct underlayment


installation techniques and avoid other common in- stallation mistakes, refer to the Rosemont, Ill.-based National Roofi ng Contractors Association.


Temperature and installation For successful underlayment installation,


temperatures must be considered. Warm temperatures coupled with dry substrates enhance the underlayment adhesion pro- cess. Cold temperatures coupled with wet substrates will not only lessen, but may even prevent adhesion. “For self-adhered products, we strongly suggest that it be 40 F and rising in order for the product to work best,” says Robert Anderson, metal prod- ucts manager at Firestone Building Products, Indianapolis. “At colder temperatures, mate- rial becomes less fl exible and won’t stick.” But hotter temperatures can be prob-


lematic too. “If it is very hot and one is in- stalling a very sticky underlayment, you only have a short time to have the sheet exposed before it becomes almost impossible to get it down fl at,” says John R. Crookston, fore- man at UpRight Inc., Kalamazoo, Mich. “It is like contact cement.” When selecting self-adhering underlay-


Installing underlayment around chimneys and other special roof features requires special instructions. (Photo courtesy of UpRight Inc.)


www.metalconstructionnews.com


Correct roofi ng underlayment installation ensures water that penetrates the exterior roofi ng materials will drain out to the exterior and away from the building. (Photo courtesy of Tarco)


ments, consider potential heat gain issues. These occur from combining roofi ng materi- als with climate, elevation, insulation and ventilation. “Metal roofi ng and rigid insula- tion/spray PU foams under metal can all contribute to a hotter roof,” says Dave Baur, product manager of residential waterproof- ing at W.R. Grace and Co., Cambridge, Mass. “Grace recommends using its Ice and Water Shield HT in hot roof assemblies. Under Cor-Ten, zinc and copper, we recom- mend using Ultra, which has a maximum service temperature of 300 F.”


June 2012


METAL CONSTRUCTION NEWS 27


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