Q: I have a stucco house built in 1959, and there is no sheathing under the stucco, only 15-pound felt over wire laced between the studs. The stucco is in great condition, but the house, built as a summer cottage, has no insulation. Not only is it cold in the winter, but mildew forms on the walls behind anything near the wall, including furniture and artwork. My questions are:
1. Can we get away with just blowing in insulation, or do we have to install a vapor barrier on the exterior to prevent the moisture from condensing on the interior walls?
2. Is the mildew in the Sheetrock permanent and should it be replaced? I’ve bleached it and painted with stain-killing moisture-barrier paint and it still came back the next winter.
3. With almost 50 years of moisture wicking through the walls, could there be other problems, like dry rot?
4. If we do have to remove the stucco, what is the best way to remove it? In the past, when I remodeled a back wall, I used a circular saw with a diamond masonry blade to cut out manageable squares of stucco and then pried these off with a wrecking bar. This works pretty well but is hard, slow, dusty work.
5. I also have the original steel, single-glazed casement windows. It looks like they have a flange behind the stucco. Is it necessary to remove the stucco, or can replacement windows be installed inside the existing frame?
6. I was told that stucco serves as a shear wall. The structure has diagonal let-in wood bracing, but I wonder if the strength is adequate and if plywood or OSB sheathing should be installed to help withstand earthquake forces. Do I have to remove the stucco or the Sheetrock, or both? I really do not look forward to removing either, but it may be the only way to address all my issues. With your help, I will face the inevitable.
A: We applaud you for thinking about tackling the "issues" with your house. Beware though, it’s a ton of work and will cost you dearly if you hire it out.
If you’re considering making it a do-it-yourself project, it’s still a ton of work, but the cost will be a lot less. In either case, plan on living with a mess for a good while as you embark on this extensive remodeling project.
The construction of your 1959 home is typical for that era — no wood sheathing under the stucco, no insulation in the walls or ceiling, and little attention to seismic concerns.
In the decade or so following World War II, the focus was on providing affordable housing and not necessarily on quality construction.
The home we grew up in San Leandro, Calif., across the bay from San Francisco, was a typical stucco box built in 1955 and very similar to your home. We remember looking at the exposed stud bays in the garage and seeing the black building paper. Our parents bought that house for about $8,000. Zillow.com said it sold recently for $570,000. Go figure.
Exterior walls were built using 2-by-4s with 1-by-4 braces mortised into the studs. The braces were "let-in" at a 45-degree angle and intersected as the top and bottom plate as well as the studs. They provide lateral stability to the wall, but they aren’t enough for seismic protection.
The substrate for the stucco was a product called K-lath. This building paper/wire combination was nailed to the studs.
Three coats of stucco were applied over the K-lath. The third coat, a color coat, completed the finished wall. The stucco does not act as a shear wall.
The only vapor barrier was the building paper. Without insulation in the stud bays, warm interior air meets with the cold wall and creates condensation and mildew.
Since the stucco is in good shape, leave it alone. Don’t worry about plywood shear walls unless you’re determined to do a seismic retrofit. In that case, contact a structural engineer to guide you.
For extra support, you can add metal diagonal braces on the interior side of the studs. These braces are L-shaped metal that are let in by cutting a saw kerf into the studs, placing one side of the L into the kerf and nailing the other to the stud.
To fully assess the situation, the drywall has to go. Simply blowing in insulation won’t feed the bulldog and may make the problem worse by creating a more hospitable environment for mold.
When the rock is off, pay attention to black staining, which is an indication of mold. If you discover mold, kill it by thoroughly rinsing the infected area with a solution of 1 cup of chlorine bleach to 1 gallon of water. Replace any rotten framing members.
Insulate the stud bays with non-faced insulation. R-13 fits the 2-by-4 cavity. Cover the wall with a continuous plastic vapor barrier of 6 mil., making sure to seal any joints or punctures with duct tape. Finally re-Sheetrock, tape, texture and paint the walls. The fungus behind the art and the furniture will be a thing of the past.
As for the windows, we don’t know any reason why the single-pane glass could not be replaced with energy-efficient double-paned lites provided that the frames are deep enough to accommodate the increased thickness of the new glass. This is something to look into, especially if you like the retro look of the steel-framed casements. Beware though, as this is a custom job and might prove to be quite costly.
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