Variation on the Bonfiglioli Wall – GWC Mag

A few years ago, Fine Homebuilding magazine published an article titled “An Easy Way to Build a Well-Insulated Wall” by Massachusetts builder Stephen Bonfiglioli. The article detailed his method of using strips of high-density foam on the interior of studs to reduce thermal bridging and increase energy efficiency. The method became known as the “Bonfiglioli Wall.”

In this Q&A post, Garrett (member B3V1156) writes that he plans to incorporate a version of the Bonfiglioli Wall in his new project in Vermont. Instead of 1-1/2-in.-wide strips of high-density EPS and 1x strapping, he plans to rip 1-1/2-in.-wide strips of his ZIP System Insulated R-Sheathing. He lists the other components of his planned wall:

LP Smartside lap siding
1×4 strapping / rainscreen
7/16-in. ZIP sheathing
2×6 wall @ 16 in. o.c.
1-1/2-in. x 1 -1/2 -in. ZIP-R furring strips (1-1/2-in. by 3-in. strips for the corners)
Rockwool R-30 batt insulation (an upgrade to the original fiberglass)
1/2-in. drywall

Garrett wants to hear from anyone who has built a similar wall system. He wonders if R-30 batts will fit uncompressed in the stud bays, if he needs a plastic vapor retarder on the inside of the exterior wall, and whether the ZIP System R-Sheathing will support the drywall. Lastly, he asks whether the ZIP sheathing will help to limit moisture problems.

The topic for today’s Spotlight: Will the Bonfiglioli wall yield the desired results?

Malcolm Taylor cautions Garrett to be aware of the modifications needed for inside corners to provide drywall backing. He also advises against using plastic as a vapor retarder, suggesting instead that Garrett rely on the local code specifications for vapor retarders. There shouldn’t be any problems with drywall support, he says, and notes that ZIP System sheathing, which uses OSB, has a lower drying…