Climate zone 6 wall assembly
Coop54
| Posted in Energy Efficiency and Durability on
I think I have finalized my exterior wall assembly for a new 2000 sf ft home in climate zone 6, and would feed back.
Walls will use advanced framed techniques, 2×6 studs 9′ high 24″oc.
Interior to exterior composition:
5/8″ sheet rock, 3″ closed cell foam insulation, 7/16″ Zip Wall Panels (taped and nails sealed), 1″ Halo Exterra Foam board (taped), Dupont Tyvek Drainwrap (taped) and lastly DiamondKote LP siding.
Is this too much or too little?
P.S. Windows and doors are avg. U-factor of 0.18, SHGC of 0.24.
Thanks!
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Replies
Coop,
I didn't know what Halo Exterra foam was, so I googled it. It seems to be graphite-enhanced EPS with an R-value of R-5 per inch.
So you'll have R-5 + R-19 = about R-24 walls. That's about code minimum for Zone 6. Nothing to brag about, but it should satisfy your inspector.
Thanks for the comment.
Have you considered using mineral wool in the wall cavities instead of ccSPF, and putting the savings toward thicker exterior foam? You could potentially have a much better performing wall assembly this way. In climate zone 6, the ongoing energy savings will likely be noticeable.
Bill
The thermal bridging of the 3" of stud (R3.6) through the R19 makes it underperforms R19 fiberglass with a full 5.5" of stud (R6.6 ) for full cavity fill.
Closed cell foam between thermally bridging studs is a waste. Applying that money to thicker exterior foam and using the cheap stuff in the stud bays is a better bang/buck. See:
https://www.greenbuildingadvisor.com/article/installing-closed-cell-spray-foam-between-studs-is-a-waste
https://www.finehomebuilding.com/2017/07/10/closed-cell-foam-studs-waste
At 5.5" half pound open cell foam uses less polymer than 1.5" of closed cell foam at about the same R-value, and air seals at least as well as 3" of closed cell foam. Also, unless blown with HFO blowing agents the 3" of closed cell foam would have to be installed in two lifts with a curing/cooling period between lifts, but many installers would be inclined to cheat that (time is money), which is a fire risk during curing, and has quality issues with shrinkage and separation from the studs. The HFC blowing agents are powerful greenhouse gases (~1000x CO2), whereas open cell foam is blown with water. The more expensive HFO1234ze blown closed cell foam doesn't have that issue (and would deliver R21 @ 3", not that you would notice after thermal bridging), and would be a better choice if you go with the original stackup.
Coop -
You don't say if you are climate zone 6 A or B? If CZ 6A, I would strongly recommend a truly ventilated rain screen assembly instead of just Drainwrap.
Peter