Available Exterior Insulation Options
Upstate NY, Climate zone 5A, new construction. I was hoping to add exterior foam insulation under my vinyl siding (vinyl siding is typical around here) to supplement 2×6 wall fiberglass batting insulation, but it seems hard to get right now. What are people using for exterior insulation currently?
I was given the following options so far:
1. Certainteed Cedarboard insulated vinyl siding, R-2.0 ($6300 upgrade)
2. A fanfold siding underlayment, R-1.5 ($750)
3. 3/4″ foil faced polyiso, R-5.0 ($2500)
4. I’ve also seen 1.5″ Owens Corning FOAMULAR XPS available at big box stores, R-7.5 (~$4000)
The first two go against the advice in articles here about exterior foam thickness, though my construction manager says they installed a ton of the thin fanfold insulation when it first came out. The third one is polyiso which supposedly doesn’t work as well in cold climates. The fourth one, my construction manager didn’t seem to like because it was so thick, he’s used to higher density foam that’s thinner I guess.
Plans also include an interior vapor barrier, which is also not recommended along with exterior foam (especially thin foam), so I’m not sure whether to tell them to put that in or not.
Any recommendations?
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Replies
Insulated vinyl siding is useless and really gives you no R value. To meet code, you will need at least R8 (2" of EPS) but most go with R10 on a 2x6 wall to keep moister from condensation levels inside the wall. Your contractor is just lazy and doesn't want to learn what many of us have been doing for many years. As for an interior vapor barrier, can you promise to never add wall hanging nail holes, ever?? Nix that one.
Thanks for the thoughts. The Owens Corning Foamular is literally the only product I seem to be able to find around here though, and I don't know anything about it. The local building supply companies say they've been sold out of all EPS/XPS for months. Any specific products I should try to look for?
I mainly use commercial roofing companies. They stockpile used EPS and you can get it for a fraction of the new price. A few holes that can easily be filled with the foam gun.