Best Approach to Wall Retrofit
I live in North Carolina, climate zone 4a and am planning improvements to slowly do myself on my recently purchased 2100 square foot 2 story 1980s home.
My walls from the outside in are masonite siding, asphalt impregnated fiberboard sheathing, fiberglass batts in 2 by 4 studs, poly sheeting (creating a wrong side vapor barrier), then drywall, so if the walls dry at all it’s to the outside.
I need to replace at least some of the siding, and find myself going back and forth between a few options:
1. just removing masonite on an as needed basis, tacking up some felt paper or other wrb like hydrogap, then nailing up matching hardie lap siding.
3. remove masonite, add new wrb, 1-2 inches rigid foam, 1 by 4 battens, hardie siding
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I'm trying to see how much change vs leaving things the same makes sense in my situation and how to make it doable for one 1-2 people with moderate building experience. My wife and I bonded working on houses as volunteers in New Orleans back in 2007 after Katrina and she's looking forward to helping me again now. Our house is already relatively efficient with a new heat pump installed right before we purchased the home this year and moisture has only been a notable issue for siding near the deck though we may find more issues as we pull back siding.
I don't think there is an easy answer here, lot of it depends on how long you will be in your place.
In Zone 4 doesn't take a lot of extra insulation to get your place to near passive house levels plus the added benefit of being able to air seal the outside of your house. This is a lot of work but not a whole lot of cost when the siding needs to be fully replaced. The flip side of this is in milder climate, the heating costs are already low so even if you reduce it by half, it is not a lot of money saved.
If the siding is one of those where you'll continue to be replacing a couple of rows each year, it might be worth it pull it all off. Working one wall at a time is not a bad way to break up the project.
If you are doing the whole siding, adding in a rainscreen makes the most sense and is does make a big difference in finish life.
The one problem with fiberboard is it is pretty hard to air seal the sheathing itself. Your main air barrier needs to be the WRB so make sure to detail this well including tying it to your foundation and to the ceiling drywall if accessible from the outside.
Thank you. We're hoping to be in this home long term. I plan on starting on the south side at the single level part of the house by the deck, the main part with notable siding damage. Adding 3/4 of an inch to an inch of rigid foam along with a rain screen makes sense for durability and air sealing, and should be doable.
I would try for 1” of exterior insulation. There isn’t much difference in code or labor between 3/4” and 1” rigid foam, so you might as well go for a bit more R value. You can save money using reclaimed material too if you can find it in your area. Polyiso is probably your best bet here, in which case 1” is about R6. If you use foil faced polyiso, it’s very easy to tape the seams. I like to use foil tape for this since it gives a clean look with the foil facing.
Bill