Spray foam and shear walls
So this months JLC has a letter from Thor Matteson concerning gluing shear wall panels to studs, quoted below.
“A letter in the June 2011 issue (“Gluing Sheathing Improves Air Sealing”) suggests attaching wall sheathing with adhesive. This could be a code violation in earthquake country. The “Special Design Provisions for Wind and Seismic” (SDPWS) governs wood-framed construction; SDPWS Section 184.108.40.206.1 states that “adhesive attachment of shear wall sheathing shall not be used alone, or in combination with mechanical fasteners.” An exception to this provision allows using adhesives in Seismic Design Categories A, B, and C, but only with a severe penalty (the entire structural system must be designed to withstand about four times the earthquake force required for shear panels attached with nails alone). Almost all construction in California falls into Seismic Design Categories D, E, or F, so using adhesive on shear panels here is completely out of the question.
Attaching shear panels with adhesive creates a stiffer wall; stiff structural systems “attract” more earthquake loads than flexible systems. Adhesive attachment robs a shear wall of its ductility, which is beneficial in absorbing earthquake energy. This increases the chance of sudden, “brittle” structural failures, which are the most devastating in earthquakes.”
I’m guessing decreasing energy lost to flex in the wall results in energy levels that could cause catastrophic failure of hardware in the load transfer paths?
Curious how spray foam would affect stiffness, since it is very adhesive and would seem to also stiffen the wall considerably, and if this could result in the same issues as with gluing the sheathing to the studs? Any ideas?
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