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Adding wall insulation to stucco clad home

Matt W | Posted in General Questions on

Martin,
I bought a 100 year old home in southern California. It is two stories (the upper does not line up with the lower), is stucco clad and has flat asphalt roofs. I have really enjoyed reading the website. If you are up for it, I have a few questions.

Location: 20 miles from the coast in zone 3 (3b I think).

The home has many exterior details that we would like to preserve, as such we need to insulate inside the home. Currently all of the interior walls are open. The exterior is clad with roughly 1 inch of stucco (the home is 100 years old so I’m assuming that it is more lime than Portland cement, but it has been patched in a few areas). The stucco is affixed to chickenwire which is directly over felt paper (1 piece I believe). The felt paper is directly over the board sheathing 5.5 in tall with ¼ inch gaps (Image 1). The space between studs is 14 inches wide but is only 3 5/8 inches deep.

Question 1
Even though it has board sheathing, it has no air gap. Am I right in assuming that the advice from this article still apply?

https://www.greenbuildingadvisor.com/articles/dept/musings/insulating-walls-old-house-no-sheathing

If so which of the methods you mention in the article (cut/cobble vs spray foam) do you favor given that the depth of the studs is 3 5/8 inches deep?

Question 2
The house has a 4 foot overhanging rooflines. Image 2

What is the amount of wall insulation that you would suggest?

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Replies

  1. GBA Editor
    Martin Holladay | | #1

    Matt,
    To answer the question of whether these walls will have water-entry problems, look for clues. You're looking for signs of staining, mold, or rot. The photo you shared looks nice and clean; if all of your stud bays look like that, you don't have to worry.

    The most vulnerable areas are the two lowest corners of each window. If there is staining under the windows, the solution is usually better flashing at the window rough openings, not retrofitting an air gap. So you can fill these stud bays up with insulation, as long as you don't see signs of historic water entry.

    In your climate, almost any type of insulation, carefully installed, should work. Most fluffy insulations will give you about R-13 in the center of a 2x4 stud bay -- that's not great, but it's fine for a retrofit in southern California.

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