wall system recommendations for zone-6
tony_build
| Posted in General Questions on
building a house in rutland county vermont.
looking for wall system recommendations, few criteria:
1. prefer low footprint of something like cellulose (would still consider foam)
2. like the idea of something like zip-r, but concerned about
(a) impact on framing tasks/tooling
(b) potential for infiltration by tunneling insects
3. trying not to exceed the comfort zone of typical area framer
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I’m building my home right now in CZ6, in upstate NY. My wall assembly is a 2x6 stud, with zip and only 1” of rigid insulation. I installed my windows in line with the zip, to keep the WRB in the same plane, so no windows bucks.
If I had to do this over again I would consider something like a double stud wall but with offset studs. For example 2x6 plates with staggered 2x4 studs. That wall you don’t have a thick walls, but still take care of thermal bridging.
Picture is from a GBA article.
that is pretty cool dennis,
u think 24 oc is sufficient for sheetrock on inside and sheathing on outside?
do you happen to have the link to the original gba article that discusses the technique?
Dennis, While your wall system may be permitted by code (IRC 2021 Table 702.7(4)), if the 1" insulation is greater than R5 and using a Class II vapor retarder, it is not a "safe" wall, in that the interior surface of the sheathing will be cold enough for condensation to occur. This means that you must be diligent with your installation of the interior vapor retarder and sealing all penetrations through it. If the R-value of your external continuous insulation is greater than 11.25, you can skip the Class II VR and use a Class III VR (standard latex paint). You can get >R11.5 with 2" polyiso (even derated for temperature), 2-1/2" GPS or XPS, and 3" of rigid wood fiber (Gutex) or rigid rockwool (ComfortBoard).
For the OP, I am personally fond of 2x6 wall construction with 3" of Gutex and I wish it were cheaper and more available. Keep your eye on TimberHP, manufactured in Maine and coming soon. 3" ComfortBoard is a suitable alternative, but still more pricey than it ought to be. If your builder is comfortable with offset double stud walls, that can also be a good option, with R-values as high as you want. For any walls, my preferred fluffy cavity insulation is dense-packed cellulose, though carefully installed rockwool or fiberglass can also work just fine.
thanks peter,
so in your scenarios:
(a) 2x6/fluff/exterior-rigid-insulation
(b) double-stud/fluff
what would the complete layering look like (eg u like zip or wrap, u like "smart" vapor barrier, etc)?
Tony_Build, I just found this information from 2012. It is the opinion of Joseph Lstiburek at Building Science Corp (a bit of a guru). This is what he said in note3 of this "article."
There are in fact some beautiful Passive Houses. But double walls are tricky to construct, increase the risk of moisture damage and in my view they don’t make a lot of sense. Give me a single advanced frame 2x6 wall with lots of insulating sheathing any day. I did the double wall thing 30 years ago before there ever was a Passive House. It was dumb then. It is dumb now.
Now, Building Science Corp has done research on double stud walls and you can read about Lstiburek’s Ideal Double-Stud Wall Design. It is in the first link below.
https://www.greenbuildingadvisor.com/article/lstibureks-ideal-double-stud-wall-design
If you would like some robust feedback on walls system, you could check out this BS&Beer (associated with GBA). They have held wall assembly competitions in 2021 and 2022. The have 2x6 wall assemblies that are evaluated. This is a link to the 2023 page and you can dig back in time to 2022 and 2021 with the menues at the top of the page.
https://www.wallassembly.com/
More articles on double stud walls
https://www.greenbuildingadvisor.com/question/double-stud-wall-midwall-air-barrier
https://www.greenbuildingadvisor.com/question/can-someone-explain-the-science-behind-a-mid-wall-vapor-barrier-on-a-double-stud-wall
Since I got blank looks from builders (and little responses), I had my builder build what he always builds (with very minor changes), then I added 2 layers of 1-1/2" XPS, which required window bucks, but gave me a house that was well insulated, even without batt insulation in the stud cavities. I carried the XPS from the top plate to the top of footing.