Wall insulation for Zone 5 (Upstate NY)
Hi,
Working with a builder on a new build construction project and have a question regarding insulation.
Architect has spec’d the walls to be 2×6, 16″ on center, 7/16″ Zip system taped green sheating, wood siding, 5.5′ mineral wool (R23) in the 2X6 cavities, with 1/2″ Gyp.Bd. on interior. Exterior will be clad in shiplap with rain screen underneath.
I’m wondering that with thermal bridging through the studs, is just filling between them with Mineral wool insulation enough for zone 5, or should I put 1.5″ rigid Polyiso on the exterior too? I believe code in the area for wood frame wall is R20 or 13 & 5.
Any advise would be much appreciated.
Thanks,
Paul
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Replies
Run a BEopt model and see if the savings are worth it to you. It’s unclear where you are at in the process, but if you switch to exterior insulation keep in mind there are a lot of other details that need to be considered like window installation, etc. While you have your BEopt model up and running you should try out different window U-values as well.
Thanks for the response, I'll run it past my builder.
Best,
Paul
That assembly meets 2018 IRC code-minimum requirements, aka the worst house you can legally build. The 2021 IRC requires an additional R-5 continuous insulation, or a couple of alternatives. I almost always find a reasonably good ROI to go above code-minimums.
Thanks Michael, appreciate your input.
Can I ask your thoughts on the roofing that the architect has proposed, I've attached a screen grab from the plan.
Should it have more insulation, or a different set up?
FYI there is an antique barn frame on the inside, but not structural, all loads are on the outer new frame.
Thanks,
Paul
Heat doesn't care about thermal bridging, what matter is overall assembly R value which includes the bridging from the the studs.
A 2x6 wall with HD batts is about an R18 assembly. Not great but also not terrible.
From that point on, generally people go up to a double stud wall (or exterior rigid if common in your area). You need a pretty large R value increase to significantly cut your energy use and double stud wall is really the simplest way to get there.
An in-between upgrade that still keeps it as a standard build is going up to 2x8 24"OC with high density batts. This gets you a 25% increase in assembly R value for the same labor and not much extra material cost.
Overall, your best ROI is air sealing. Getting your air barrier continuous across all cross sections and making sure they are executed properly is what will make the biggest difference in the end. You don't need passive house level air sealing but 1Ach can be hit with a bit with a bit of upfront design and elbow grease.
Thank you for this insight. I'll share it with the architect and builder.
Were you able to see the attached roof detail and have any thoughts?
Thanks,
Paul