Using nailbase panels as wall sheathing
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I’m considering framing a large addition with 2×4 studs (actually, engineered studs) 24″ OC with open cell spray foam in the cavity, with a exterior application of 2″ nailbase (1 1/2″ foam with OSB sheathing attached). My question is whether the nailbase will serve the lateral bracing function of typical sheathing, given that it will be separated by the 1 1/2″ of foam to the studs. In other words, can I just use nailbase without adding a redundant layer of sheathing directly applied to the studs?
My thinking is that this is a fairly efficient and reasonable cost wall in terms of labor and materials. Located in the Boston MA area.
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Replies
David,
The manufacturer's specifications would probably be the best place to get an answer to that.
David,
If the nailbase manufacturer can't help you, you might need to talk to an engineer.
Many builders install nailbase on walls, but the typical application is for a retrofit project (where the walls have existing sheathing to provide bracing). For example, see A Deep Energy Retrofit Using Nailbase Insulation Panels.
I visited a house in Michigan that used a wall assembly very similar to what you are proposing here. One distinction is that they used EPS foam covered by plywood sheathing as opposed to a nailbase product which has the two layers pre-bonded. Near the corners, they used a second layer of plywood sheathing directly attached to the studs to provide lateral support. The thickness of the EPS in those areas was reduced accordingly. They had an engineer determine how much distance around each corner needed the second layer of sheathing. The builder stated that they usually prefer to use diagonal bracing for the lateral support, but that did not work with the window placements in that particular house design.
When the OSB is on the exterior side, the fastener spacing & type have to be engineered to give the wall sufficient shear strength. (Huber ZIP-R is a very thin nailbase panel, and the fasteners & spacing are specified by the manufacturer for structural sheathing applications.)
If you use let-in bracing or shear panels to establish the structural capacity of the wall, you can then just use the standard fastener & spacing for the nailbase panels specified by the manufacturer.