Replies

1. GBA Editor
   Martin Holladay | Apr 27, 2019 05:43pm | #1

   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.

2. 
   Coop54 | Apr 27, 2019 05:48pm | #2

   Thanks for the comment.

3. Expert Member
   BILL WICHERS | Apr 27, 2019 08:52pm | #3

   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

4. Expert Member
   Dana Dorsett | Apr 28, 2019 09:02am | #4

   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.

5. 
   Peter Yost | Apr 28, 2019 12:35pm | #5

   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