Insulating an old stucco wall
ptombarrett
| Posted in Energy Efficiency and Durability on
I’ve recently gutted the kitchen in my 1955 era stucco box. The Kraft paper on the inside of the stucco has fallen off in a lot of places. I want to insulate. Do I need to do something to protect the insulation from any moisture wicking through the stucco now that the paper has deteriorated and bare stucco present? I live in the Sacramento Valley in norther California.
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You do have to be careful when insulating old stucco houses, because the moisture dynamics change. Water can soak through stucco, but most stucco leakage comes in through small or large cracks and unsealed seams around penetrations (doors, windows, hose bibbs, etc.). As you have noted, your house is built like most post-war houses in CA and it has no building paper or other moisture barrier behind the stucco. Many of these houses have no flashings or sealant joints either. In your semi-arid climate, this generally doesn't cause issues for these houses because the walls are well ventilated.
However, this can all change when the wall is insulated. When you insulate a wall, you also reduce the airflow and heat flow through the wall - that's the whole point. Unfortunately, it was that airflow and heat flow that worked until now to dry out the water that has inevitably gotten in. Take that away and walls may become wet enough for long enough to start causing moisture problems where there were none before.
Short of removing and replacing the stucco, there isn't much you can do to change these fundamentals. You could install a few inches of foam insulation and then a new stucco finish over that (either traditional cement stucco or newer synthetic stucco, aka EIFS). Done well, this can be a durable fix but it is pricey and it requires careful attention to aesthetic and moisture detailing around penetrations.
If those are out of the question, you can read about the current "best practice" approaches to this sort of project by searching this site for articles about insulating walls with no sheathing. These provide good guidance on maintaining some level of drying potential in unsheathed walls.
You climate does work in your favor. Having 9-10 months of dry weather really helps in drying out moisture that may accumulate during those rare week-long winter storms.
i am curious whether painting the exposed interior of the stucco with a moisture permeable air barrier like Henry 17MR would be a good idea. i'm guessing the exterior stucco would require a weep screed to be installed so the the mudsill doesn't rot.
Thoughts?
I wouldn't bother with painting the inner face of the stucco. It won't do much of anything to reduce moisture seeping through minor (or major) cracks, and it would be PIA.
I also wouldn't try to add a weep screed or other edge hardware in the existing stucco. Without a drainage plane to limit intercept bulk moisture, they won't work as intended and it is a huge undertaking to install these in existing stucco. Your stucco is getting pretty old and it is likely that the wire reinforcement is rusted and brittle. Once you start cutting into the stucco, there's a high probability of doing more damage than you fix. And, if you have the budget to do this sort of cut&patch and refinishing, you would be better off removing the stucco and installing new siding, stucco or otherwise.