Insulating balloon frame stucco Four Square
How do I airseal my ~100 year old stucco four square?
I like my plaster walls, though there are some that need work.
I know previous administrations had put in quite a bit of blown cellulose. It appears to have uneven settling. There was also quite a lot blown into the attic which I think is pressing down on the keys to the second floor ceilings. I know the ceilings and the bearing walls need to be addressed. Anecdotally I know its not working well as some of the walls get very cold during our Chicago winters.
I have identified the chases for plumbing, electrical etc. And most if not all penetrations.
I know the window casings need to be identified.
I am guessing there are exposed cavities behind the exterior walls all the way to the attic. I know that all the studs are not on 16 inch centers, though they are true 2×4’s.
I’ve been using the older version of the airsealing from Fine Homebuilding as a guide, though even since the recent revision building science has advanced quite a bit. My primary concern is tightening up the building envelope, my goal is less than two ACH, but I don’t want to spend on a blower door test until the big issues are addressed.
I realize there a many great techniques for building new homes very tight, but the opportunity is in homes like this. Any help or directions would be greatly appreciated.
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Replies
The details of the wall's material stack up matters (a lot) with stucco siding.
Is there a plank sheathing layer on the exterior? (If not, is a problem!)
If yes, is there any rosin-paper/tarpaper/other broad-sheet layer on the exterior of the sheathing?
Is there an air gap between the stucco & sheathing?
All too often 100 year old stucco cladding is on wood lath nailed directly to the studs, an approach which relys on the empty stud cavity as a capillary break and drying channel. Filling those stud bays full of cellulose can draw bulk water into the assembly and create problems well beyond the mere settling issues that high moisture level cycling creates for the insulation.
Thanks for the reply, unfortunately the house came with blown in Cellulose.
The stucco is on wood lathe
I will check on the sheathing but I think it does have planks
I am assuming there is an air gap as the house is pretty dry. We also have large > 2ft overhangs.
Are the any resources, written or web on what the issues are?
The deep overhangs help with limiting rain wetting, but it's not a complete solution. (Dew wetting matters too.)
The air gap is a necessary capillary break for keeping the structural WOOD dry, not the interior of the house. The interior of the house can still be pretty dry even as the exterior edges of the framing, lath, or sheathing begin to rot away. See:
https://www.greenbuildingadvisor.com/article/to-install-stucco-right-include-an-air-gap
Disaster scenarios rarely develop over night, it usually takes years or even decades to become a structural problem. But it's worth figuring this out sooner than later, in case mitigation measures need to be taken to keep the house from slowly deteriorating.
A no-gap-no-sheathing house with stucco on lath nailed directly to the studs with cavities full of cellulose, could be "fixed" by adding a continuous layer of 1" (or thicker) of foil faced polyiso over the exterior strapped to the wall with 1x4 furring through-screwed to the studs with pancake head timber screws, mounting new siding onto the furring.
The window flashing needs to be adjusted to direct bulk water into the air-gap between the polyiso and siding, and there would be a lot of trim that needs re-doing, but that only adds ~2.25-2.5" to the total wall thickness (depending on the new siding, which is usually do-able. If that's too thick, a layer of 1/4" rainscreen mesh (eg Obdyke Rainslicker) on the between the foam and new siding may work, using longer fasteners to secure the new siding. (There will be issues to work out for long-nailing/screwing through the stucco- not all siding types would work.)
Before going into more what-ifs, figure out what you have and report back.
Appreciate the reply and have since come across a couple of questions like mine. The pot of gold is that there are at least 500 homes like this where I love.
I will figure it out. There is plenty of other lower hanging fruit, before we add another layer of sheathing. Your comments are very helpful.
John