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Community and Q&A

Should I install insulation?

liz_lee | Posted in General Questions on

My house in LA is about 100 years old and there is no insulation within exterior stucco walls.

I’m debating whether I should install insulation (these pink sheets sold in home depot) since I have a chance to do so.

The stucco looks pretty thin to me. If rain water gets into these pink materials, would it cause fungus growth or maybe bugs build a nest within? A house has its own working built in ventilation and functioning mechanism for 100 years. Maybe I should not disturb it.

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  1. davidmeiland | | #1

    You should probably consider cellulose insulation instead of XPS (the pink foam board). You are right to be concerned about changing the way the walls work, in terms of moisture movement. If you have the walls open, you are in a good position to determine whether there have been water infiltration issues. Any active leak could pose a big problem if you fill the stud bays. On the other hand, proper insulation will make the house a lot more comfortable.

  2. GBA Editor
    Martin Holladay | | #2

    A few questions:

    1. What does "LA" mean? Los Angeles or Louisiana?

    2. What are "pink sheets"? Are you talking about fiberglass batts or Owens Corning brand XPS (a type of rigid foam)?

    3. What kind of access do you have to these walls? Are you planning on replacing the stucco? Or are the stud bays open on the interior side?

  3. Dana1 | | #3

    How to best insulate antique stucco depends a lot on the exact stackup of the wall assembly. Stucco retains a lot of rain & dew moisture, then releases it quickly when sun-warmed.These high-intensity moisture bursts are best managed with a ventilated air gap between the stucco-lath and the next layer in.

    Many stucco clad homes 100 years ago had wooden lath nailed directly to the studs, with no intermediate layer, and the stud bay cavity provided the drying path, which works. But you don't need a 3.5-4" of ventilation space- 1/2-3/4" will do. But creating that space usually requires a full-gut rehab of the interior.

    Other stucco stackups of the era had the stucco-lath with an air-gap (sometimes only ~1/4" between the stucco and a tar paper or rosin paper layer covering plank sheathing. If the air gap is deep enough (a half inch is good) AND the paper layer is a tar paper / fasphalted-felt (and not rosin paper) it can usually be safely insulated with blown fiber insulation.

    But there are variations on the theme- what do you have for a stackup?

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