Best way to insulate old farm house walls
We live in zone 6b and just purchased an old farm house. The clapboard siding needs to be replaced and I would like to upgrade the wall insulation and address air infiltration problems at the same time. Currently there is blown in cellulose. The walls are lath and plaster, 2×4 studs, 1” boards, tarpaper, siding. Keeping the original look of the house is very important to us and we would like to keep the original trim as much as possible. My thought is to remove the exterior boards and all the cellulose, spray foam the stud bays with closed cell foam then install zip system 1” r sheathing over the studs. I haven’t priced any of it out yet but I imagine it’s going to be very pricey. This would keep the wall thickness close to original and therefore less hassle when dealing with the trim around the eves and window boxes. Does this plan make sense? Is there a better or cheaper method?
Thank You
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Is the board sheathing in good shape? If so, you could leave it and the existing cellulose in place (perhaps adding more). Then you could improve things significantly by installing R-7.5 of reclaimed rigid foam on the exterior. (Reclaimed foam is generally much less expensive than new product.) This would be a much greener and cost-effective approach than spray foam (especially as compared to older closed cell products that use problematic blowing agents).
You may want to search GBA for articles and discussion threads on doing a "deep energy retrofit." The more recent ones often argue for focusing on practical steps that improve comfort and performance without blowing up the budget.
If you avoid overspending on your project, you may be able to install a solar array and offset most or all of your carbon footprint. There are many variables to consider, but GBA is a great resource for planning how to move forward.
In 1993, we bought a broken down 200 year old farmhouse in Maine. Over the years, we fixed stuff, replaced stuff, rebuilt stuff. We spent lots of money and ended up with a nice, but inefficient house. The only lesson we took from the experience is the need to have a long term plan, so you do what needs to be done in logical order, as finances permit, focusing on the major stuff.
Start with permanently improving the building envelope. First, what is your air sealing plan? Get a blower door test. You'll be appalled, but get info on where to start to tighten up the place.
Move on to thinking about insulation. Closed cell foam is expensive. I agree with Steve. Exterior foam makes a lot of sense. Take lots of photos so yo can replicate the trim if you want, but plan on removing it. Unless Frank Lloyd Wright designed your house, do you really care if your renovation is authentic? Our house was designed and built by some nameless farmer. It was obviously renovated repeatedly over the years, but anyone but an expert can look at it and think it's a nice Federal style house, in spite of the various trim pieces from several late eighteenth and early nineteenth century styles.
Three or four inches of foam wouldn't be a bad idea.
A few years ago, we got smart and built new:-)
I appreciate the advice. The exterior boards are in fair shape, a few would need to be replaced but that’s not a big deal. If I just added the insulation on the outside of the exterior boards is there a concern that there isn’t a vapor barrier on the inside between the cellulose and lath and plaster? The other concern I had about going that route is the roof overhang is not very big and I didn’t want to reduce it anymore if I didn’t have to. It is a two story home. I will do more reading on those deep energy retrofit articles.
Thank you
Fomocosho,
Q. "If I just added the insulation on the outside of the exterior boards is there a concern that there isn’t a vapor barrier on the inside between the cellulose and lath and plaster?"
A. No. For more information, see these articles:
Do I Need a Vapor Retarder?
Vapor Retarders and Vapor Barriers
Yarding out the cellulose and replacing it with closed cell foam is an expensive waste of high performance foam (that comes with a high environmental impact) that buys you very little additional performance, due to the thermal bridging of the studs. Save the high R/inch budget for going fatter exterior foam. See:
https://www.greenbuildingadvisor.com/articles/dept/musings/installing-closed-cell-spray-foam-between-studs-waste
http://www.finehomebuilding.com/2017/07/10/closed-cell-foam-studs-waste
In zone 6 with 2x4 framing you'll need at least R7.5 on the exterior for dew point control, R8 if it's full-dimension 2x4s. If you're stripping the plank sheathing you'll be able to inspect the cellulose and fix any gaps, and you'd be in a position to upgrade the window flashing, If it's full-dimension 1x plank sheathing, the 2" ZIP-R would give you the necessary R value for dew point control on 3.5-4", adding just an inch to the total wall thickness.
Fomocosho,
If you have only a minimal roof overhang, that might be a reason to choose metal roofing the next time you re-roof. It's easier to add a few inches of overhang with metal roofing than with other types of roofing.
Thank you for your replies. I got a quote for zip r panels they said 2” is not available but 2 1/2” is. They are $64 per panel and must be ordered in bundles of 18. This does not include the tape. They are R 12.6. This seems quite steep if I compare the cost of separate osb, foam, house wrap. The savings for me would be the ease of installation as this will be diy. I just thought someone might find the pricing info useful.
I agree taking the cellulose out would be foolish after your comments and more research, but I would want to do like Dana said and fill in any voids that are existing.
In the zip panel literature it says panels used on lateral shear walls need to have solid framing or blocking on all panel edges. Excuse my ignorance but how do I know if this applies to my home?
Thank You
The material cost of ZIP-R is high, but the labor costs of installation are pretty low compared to separate layers. The skill levels demanded for detailing those separate layers is also higher.
Many balloon framed antiques will have angled let-in bracing for shear strength.
https://renaissanceronin.files.wordpress.com/2010/03/balloon_framing.jpg