House Wrap

Published on June 4th, 2013 | by Henri

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Housewrap and foam insulation on new second-floor

Q.    I am adding a second floor to my house. The builder used OSB sheathing for the outside walls. He wants to install Tyvek housewrap to cover the OSB sheathing. The siding contractor wants to install 1/2-inch Styrofoam rigid insulation before the vinyl siding.

What do you recommend? Shall I have the Tyvek installed before or after the Styrofoam? Do I need both? On the first floor I have fiber cement shingles. Shall I install the Styrofoam insulation/housewrap on top of the old siding or shall I remove the old siding first? I want to install the new siding as soon as the builder is done with the roof and exterior walls.

My preference is to remove the old shingles (even if it costs more) and install the siding the same way as in the new second floor. My wife and I like Foundry shakes/shingles (they come in 7×60 and 10×60 inches). The builder says that I can’t use both Styrofoam and housewrap because the house “has to breathe.”

A.    There is no problem using both housewrap and rigid insulation, but housewrap is not needed if you tape the insulation’s joints with a waterproof tape (not duct tape). OSB is an adequate air barrier.

Instead of the 1/2-inch Styrofoam the contractor wants to use, suggest installing 1-inch thick Styrofoam — same labor cost but double the energy efficiency.

It is best to remove the cement siding to give you a smoother job. Nailing through cement shingles can break them and result in an unsatisfactory end product.

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