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Community and Q&A

Is air sealing still needed when adding exterior foam?

vzS7PFG8DN | Posted in Green Building Techniques on

We are currently at the framing process on our new home. ~1900 sq-ft., ICF basement (unfinished).
~1900 sq-ft main level and 800 sq-ft upper level. Located in Zone 5B central UT.

Most of the exterior will be stucco and I plan on having 2.5″ of foam installed underneath on top of the 7/16″ sheathing (2×6 walls) I was able to foam gun most of the sill plate to top of foundation as wall as the side bottom edge of the rim board all the way around.

Do you think it would be worth using Eco seal or spray foam around the sheathing seams? Or will exterior foam and the stucco layer prevent any air infiltration?


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  1. GBA Editor
    Martin Holladay | | #1

    Every house needs an air barrier. The air barrier needs to be continuous, without seams or breaks: under the bottom floor, around the walls, and across the ceiling.

    Here is more information on air barriers:
    Questions and Answers About Air Barriers

    One Air Barrier or Two?

    Airtight Wall and Roof Sheathing

    There are lots of ways to build an air barrier, but you need to know where your air barrier is. If you want to use your wall sheathing as your air barrier, you can. If you want to use your rigid foam as your air barrier, you can. It's even possible to use your housewrap as an air barrier.

    But you need to know which layer is your air barrier, and you need to be sure that layer is tight. If you want to use rigid foam as your air barrier, then the perimeter of each sheet must be sealed. Ideally, that means using a bead of caulk at the perimeter of each sheet, plus special high-quality tape to seal each seam.

    Finally, some people include two or three air barriers in their wall systems. You can do that, too, if you want. Extra air tightness measures are always good. The better your air sealing work, the lower your air leakage rate, and the better your home will perform.

  2. wjrobinson | | #2

    Rigid foam unlike sprayfoam is not glued to substrate. So rigid can be air leaky in many ways. Around here it is applied in two taped layers. And with the experience of doing many many homes they have worked to do trouble spots better over time. Good luck. Watch GBA videos and or join too for detail sheets.

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