GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter Instagram YouTube Icon Navigation Search Icon Main Search Icon Video Play Icon Audio Play Icon Headphones Icon Plus Icon Minus Icon Check Icon Print Icon Picture icon Single Arrow Icon Double Arrow Icon Hamburger Icon TV Icon Close Icon Sorted 汉堡/搜索图标

Community and Q&A

Evaluating the Bonfiglioli Wall for Climate Zone 6

Johngfc| Posted inEnergy Efficiency and Durabilityon

Zone 6b, Colorado

Elev: 7300’, ~ 22”/yr precipitation (~ 50% as snow)

~7500 HDD now but declining ~ 37 Days/yr (1980-2019 data)

The site faces S, on a S-facing hill, full sun, and warm for the area.

Would/could a Bonfiglioli wall (B-wall) as described in FHB:https://www.finehomebuilding.com/membership/pdf/9750/021250059.pdf) be suitable for this CZ6 location? The wall is (inside to outside): drywall, vapor retarder (e.g. MemBrain), 1×3 aligned with studs, 1” foam strip on stud, 2×6, sheathing, WRB/rainscreen, cladding. Reportedly R-30 with high-density fiberglass in the stud bays (no foam), and requires careful air sealing.

I’ve seen//m.etiketa4.com/article/efficient-walls-budgetbut I didn’t note any evaluation of the suitability of the B-wall for CZ 6. It’s clearly advocated (by some) for CZ5, but appears non-compliant with IRC and other GBA discussions – e.g.//m.etiketa4.com/article/calculating-the-minimum-thickness-of-rigid-foam-sheathing, which advises exterior foam at least R-7.5 for 2×6 walls in CZ5 and R-11.25 for CZ6. Lstiburek (repeatedly) advises against a wall where the sheathing is cold (but has a double-stud with sheathing in the middle://m.etiketa4.com/article/lstibureks-ideal-double-stud-wall-design).

Related://m.etiketa4.com/article/is-cold-sheathing-in-double-wall-construction-at-risk– long and detailed discussion for _thick_ walls. Martin (comment #27) says external insulation was (at that time) allowed throughout the US. In our area, IRC 2018 applies.

Questions:

1.Is a B-wall suitable for my CZ6 location? I’ve been leaning to 2×6 with 2″ of external form or rock wool, but the B-wall looked interesting, if it’s safe.

2. Can a B-wall actually achieve R-30 with fiberglass, as claimed?

3.With the B-wall, would there be a noticeably lower risk using dense-pack cellulose rather than fiberglass?

4.The B-wall isn’t consistent with IRC CZ6 guidelines for external insulation (20+5, 13+10). Is external insulation always required by code in CZ6? B-walls, Larsen and double-stud walls seem to be promoted for cold climates without external insulation. (a) Is moisture likely to be a problem with the B-wall described above, and if not, why? (b) Is there an exception to IRC and other guidance (E.g. Moisture Control Guidelines 2020 – ABTG Research Report No. 1701-01) for these walls?

5.With declining costs of PV, increasing ASHP efficiencies, and warming trends, is there a comfort or financial case for ~R-40 over ~R-30 (U 0.025 vs U 0.033) walls in a “warm” zone 6 location? Would improved glazing likely be a better investment?

GBA Prime

Join the leading community of building science experts

Become a GBA Prime member and get instant access to the latest developments in green building, research, and reports from the field.

Replies

  1. Jon R||#1

    Make sure that the wall complies with the recommendations in Table 2 A or Bhere.

    No, code doesn't require exterior insulation. But it's a good idea. So is cellulose (vs fiberglass).

Log in or create an account to post an answer.

Community

Recent Questions and Replies

  • |
  • |
  • |
  • |