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Community and Q&A

Insulation for Stucco House

Irdabo | Posted in General Questions on

We are gut renovating a historic stucco home in MA that has a 2×4 construction with no insulation. The architect is proposing closed cell insulation. I was reading that CC insulation can be problematic if it encounters moisture and can’t breath. What’s the best way to insulate here? Should we add a vapor barrier internally before CC insulation? Should we use open cell? Consider some other form of insulation?

I’ve read about other concerns with spray foam related to it not being the most “green option” due to the manufacturing process and some people reporting health risks. Not sure if I’m over thinking things here.

Help! Please advise.

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  1. GBA Editor
    Kiley Jacques | | #1

    Builder and GBA Expert Member Josh Salinger answered this question for another reader, saying: "Closed cell spray foam will work fine in this application so long as it doesn't contact the back of the stucco. The tar paper is serving an important function as it is creating a small but important gap between the stucco and (in this case) the framing. Stucco applied to wood frame walls is a 'drained wall' vs. a 'mass wall' so historically two layers of tar paper were applied which allowed for this drainage. Ideally this gap is paired with a through wall flashing, but in your case you are stuck with what exists."

  2. 1910duplex | | #2

    I thought that any wall insulation in a historic stucco house was problematic, because of moisture issues?
    My duplex is portland cement stucco over metal mesh, over tar paper (presumably) over diagonal wood sheathing. Interior is plaster.

  3. Expert Member
    PETER G ENGLE PE | | #3

    Adding insulation to any old house can be problematic for moisture issues, as many of these houses lack necessary flashing and drainage details. If you can verify from interior inspection that there are no (zero, zilch, none at all) bulk water leaks, then insulation generally won't cause problems. Closed cell can work inside a wall with stucco cladding, and will generally help a bit with air sealing as well as adding insulation value. Fluffy insulation can also work well if you detail the drywall as your air barrier and use a VR paint, or use a smart membrane behind the drywall as the air/vapor retarder.

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