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What is the best way to insulate a 1969 stucco home in the San Francisco Bay Area? I have added a lot of insulation in the attic area but the rooms and walls are cold. Any suggestions?

  • You get what you got. Sorry. When you buy an uninsulated home, that is your choice. Now you have to live with the choice you have made (or sell the house and buy a different one). – Tyler Durden Jan 22 '15 at 22:32
  • There's massive risk in insulating walls on an old stucco house like that, as the iLikeDirt answer goes into. I have learned this the hard way, in the San Francisco Bay Area also. – Bryce Dec 26 '17 at 18:42
  • My mom lives in sebastopol, her 1940's era home is stucco, she had the walls filled with insulation over 40 years ago, the company drilled holes in each stud bay and added a measured amount of insulation, I remember they said they measured it to know if there was blocking in the wall and a 2nd hole would be needed, then they patched the holes. I thought the insulation would settle and not be very effective, a few years ago I helped my step dad repair a bathroom and we needed to remove part of a wall, I was amazed that the insulation had not settled and no problems 40 years later. – Ed Beal Dec 27 '18 at 14:45
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I assume you mean to insulate the walls. Houses of that vintage often had no insulation between the wall studs. The easiest way to insulate them without wrecking the stucco or drywall is to drill holes through one or the other at the top of the stud bay and blow in cellulose insulation.

However, when you do this, you impair the ability of the wall to dry when it gets wet, since there's less heat flow and less air flow through those empty cavities--both of which promote drying. This isn't much of a problem with a modern wall where the stucco is separated from the wood with tar paper or housewrap, but in an old house like yours, oftentimes the stucco was applied over wood lath with no tar paper separating it from the board sheathing; in fact, in many cases, there was no sheathing at all! They simply nailed wood lath to the studs and stuccoed it.

In such a wall, adding blown-in cellulose insulation can be a problem when the stucco gets wet, since it can't dry as easily, and cellulose itself is capable of storing water. The risk of this approach depends on the climate and the construction. If your house is in rainy San francisco, it's riskier than in Campbell or San Jose. If your house has no sheathing and/or no tar paper under the stucco, it's riskier than if it did.

In such borderline cases, the prudent approach, if you really want to insulate, would be to remove all the stucco, install batt insulation (fiberglass or mineral wool) between the exposed studs, then install plywood sheathing, wrap the house in tar paper or housewrap, apply 1+ inches of rigid foam or mineral wool insulation over that, then nail 1x3 furring strips over that, and then apply new stucco or siding over the furring strips. Obviously this would be the most expensive option but it would result in a very well insulated wall and have zero risk of mold or rot.

  • The other issue I've seen with blown-in for walls is return on investment. For a medium sized home, you are looking 3-4k for someone to do the job and in such a moderate climate you will only see a savings of $100-200 on the heating bill over the winter. – diceless Jan 22 '15 at 20:51
  • I advise people to stay away from foam jobs for house like this... wouldn't even think about using blown-in cellulose. Heat readings after spending tons of money and opening 100s of holes in a house aren't much better than the before readings (and many of the foams are toxic). – DMoore Jan 22 '15 at 20:57
  • My preference is no foam as well but rigid mineral wool could work instead. That said, I agree with both of you that cost-effectiveness of any such projects in the poster's region is questionable. – iLikeDirt Jan 22 '15 at 21:00
  • No such thing as "zero risk". Also your plan requires extending window frames, a big job that could easily be screwed up resulting in mold or rot. – Bryce Dec 19 '17 at 7:18
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Not everybody would be ok with the aesthetics, but this is my family's solution to unrelenting cold bedrooms: 2" pink/purple rigid foam cut to size for the inside of 1 exterior wall in the bedroom. We squeezed it in place between the ceiling and the top of the hot-water baseboard radiator. The room has been comfortable for the last 2 winters. We put the printed words on the insulation towards the wall, at least. Not elegant, but frankly, it's in budget and warm. My Mom likes the color. We're very chemically sensitive and this foam seems very inert. Rainy central NJ. -5 F to 105 F temps.

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