The Real Deal
Practical solutions for sustainable building with Steve Easley
The application of spray foam products—such as NCFI’s InsulStar spray-foam, which is shown here— provides added uplift resistance to a house.
this traditional fashion with 6d smooth nails at a 6”/12” nailing schedule (this means a nail every 6” on panel edges and every 12” in the field of the panel). His research shows that the applica- tion of the closed cell spray foam (2 lb. per cu. ft. density) provides about the same benefits as increasing the nailing schedule from a typical 6”/12” schedule to a 6”/6” schedule. What I found most impressive was that it provides almost as much uplift resistance—about 178–209 lbs. per square foot—as 8d ring shank nails placed at a 6”/6” schedule at 205 lbs. per square foot. Dr. Prevatt’s group also evaluated ap-
plying 3” fillets of closed cell spray foam along the truss and sheathing intersec- tion, essentially gluing the sheathing to
48 GreenBuilder July > August 2010
the upper truss chord for the length of the roof truss. This 3” x 3” triangular fillet doubled the uplift re- sistance for a 1/2” OSB sheathing fastened to 2 x 4 framing at 24” O.C. compared to the same system with a 6”/12” nailing schedule.
Five roof attics under test at the University of Florida. For more details on the project, contact Dr. David O. Prevatt at
dprev@ce.ufl.edu
More Help on the Way Dr. Prevatt and his research group are engaged in new research to evaluate the impact of water leaks to the system. The University of Florida team will be
looking at the effects of moisture content of the wood sheathing and framing and its bond with the foam. These tests will intentionally introduce water leaks to see if leaks com- promise the system. In storm-prone areas, it makes sense to use peel-and-stick membranes to provide secondary water resistance under
roofing materials as opposed to standard underlayment. Of course, always follow the roofing manufacturer’s recommendations. If the shingles are lost, you still have some pro- tection against leaks. It makes sense to take a “belt and suspenders” approach to build- ing and retrofitting homes in storm-plagued areas. GB
Steve Easley is owner of Steve Easley & Associates, a nationally recognized building science consultant who specializes in green and best practice building. Contact him at
steve@steveeasley.com
www.greenbuildermag.com
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