Learn how to fasten and air-seal rigid-foam sheathing
to the outside of an existing house
with David Joyce
David Joyce: We’ve stripped the house of all the siding, we’ve put on the housewrap, and now we’re applying the two 2-inch layers of polyisocyanurate.
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Insulation Retrofit Complete
Narrator: Using multiple layers of foam rather than a single layer of thick foam helps you get a better air seal, because you can offset the seams on both edges of the sheets. Start with a 2-foot rip at the bottom of the wall and stack a full sheet on top of it. The next layer will begin with a full sheet. Take a little time to square up the first sheet so that the corners are good and plumb. This way, you won’t have to cut all the factory edges from the subsequent sheets. There are a lot of obstructions on the outside of a house—spigots, electrical conduit, meters. Some can be worked around; some need to be moved. If a spigot is too short to absorb an extra 4 inches of wall thickness, cut it off and replace it later. Dave likes to use roofing buttons to hold the foam to the walls. In this video, his crew uses spikes and screws interchangeably. Now they use screws exclusively. Screws are easier to remove, if needed. Screws are also easier to adjust. One of…