Bonfiglioli Wall Advice
Hello, I am finalizing some details for a Bonfiglioli wall system on a build in Vermont, zone 6B. For the rigid foam furring strips, I have decided to use 1-1/2″ Zip R that will be ripped into 1-1/2″ strips at studs and 3″ strips at corners. This is to act as the substitute for the traditional 1-1/2″ rigid nailed to 1×3 furring. From exterior to interior, the wall system will be as follows.
– LP Smartside lap siding
– 1×4 strapping / rainscreen
– 7/16″ Zip sheathing
– 2×6 wall @ 16″ O.C.
– 1-1/2″ x 1/2″ & 1-1/2″ x 3″ Zip R furring
– Rockwool R30 batt insulation
– 1/2″ drywall
Wanted to know if anyone has built a wall system similar to this, whether exact or hybrid to how I’m thinking. Also was looking for some advice on additional detailing and concerns such as:
– With the use of 1-1/2″ ZIP R for furring, will compressing the R30 Rockwool to fit in the wall cavity be problematic?
– Will a plastic vapor retarder be needed on the inside face of the exterior wall? or can proper paint on drywall bypass this?
– Will the strips of ZIP R provide enough support for the drywall?
– Will the use of 7/16″ ZIP wall sheathing be a good fit with this assembly? (want to limit potential moisure problems with a cold sheathing)
Thanks,
Garrett
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Replies
Garrett,
- Any walls with interior strapping mean you need to modify the standard framing details at inside corners and wall intersections to provide backing for the drywall.
- R-30 Comfortbatts are 7.25". Can you clarify how thick the Zip-R you are using is? Your post is a bit unclear.
- You never need to use poly. Your code will specify what level of vap0ur-retarder you need. The options run from a variable-perm membrane, to vapour-retarder paint.
- Zip sheathing is very lightly attached to the foam backing and relies on fasteners to keep them together once installed. The same is true when you use it for Bonfiglioli walls - you can't rely on the glue to keep it together, but properly fastened it is fine for drywall.
- Zip sheathing is fairly low perm, meaning the walls don't have the same drying potential as those sheathed with plywood.
I did this on my house that had 2x4 walls. 1-1/2 inch thick foam board and 3/4inch plywood both ripped to 1-1/2 inch widths.
I did two bedrooms relatively quickly. Ripped it all, then used a ~2+ inch 15guage nailer to tack the foam strips to the studs and then framing nailer to secure the plywood strips. Went with a mineral wool batt and vapor barrier.
Really happy with how it turned out!
AD,
I think that's where Bonfiglioli walls shine - as a way to retrofit depth to existing walls, and pick up a bit of R-value at the framing. I'm not sure I'd choose them on new construction, given the alternatives.
Thank you Malcolm and DCcontrarian! Nice to meet you guys. Great Information.
Yes Malcolm, I wouldn't choose what I did for new construction. It reduced the room size and extra work with electrical boxes.
Mine was a renovation of a 2x4" wall house in Anchorage. I was really shooting for more depth. The original 1953 wall system just had paper backed foil behind the drywall! This wall system made a huge difference in comfort immediately. Continuous exterior foam still might be in the future, who knows.
I think your assembly is fine. But I want you to look at whole-wall R-values before committing to it.
Framing wood is about R1.25 per inch, so a 2x6 is R6.9. With R5 Zip you get R11.9 for the framing. If you assume a 15% framing fraction you get an assembly R-value of 24.4. If you just framed the wall with 2x8, 7.25" of wood is R9.1, you get an assembly R-value of 22.3. So the Bonfigioli is increasing your assembly R-value by slightly less than 10%.
Alternately, you could get the same R-value with 2x8 framing and a 10% framing fraction, which you might get with 24" stud spacing.
Another alternative would be to do 2x6 framing with 1" of continuous insulation either on the inside or outside. With 15% framing fraction you get R22.0 with R5 of continuous.
My point is that thermal bridging is often overstated as an issue.
Thanks for the reply, DCcontrarian. If I was to run the 1" of continuous insulation on the inside, is there a recommended direction / approach for the sheets to be installed? Should 1x furring strips be used as cavitities for the 1" - 1.5" insulation (kind of like furring in an exterior wall)?
Here's what I was thinking: a 2x8 is 1-3/4" wider than a 2x6. It's just easier if you keep your wall to standard dimensions. So the reason I said 1" insulation was I was thinking of 1x3 furring strips between the foam and the drywall. You can run the furring either way but I find it easier to run them horizontally.
Whether to run the insulation sheets horizontally or vertically is really a religious question...
I would seriously consider an offset 2x4 on 2x8 plates. It is so nice running electrical and plumbing through. And of course thermal benefits. And 2x4 are cheap.
I'll admit that I drank the BonFig Kool Aid and built a new construction wall similar to this. Would I do it again? Maybe if I was renovating a 2x4 wall, but not for new construction.
-It made the walls a little less flat so had to spend more time shimming before drywall.
-Extra time on the build. Yeah, it seems fast but you have to account for all the windows and any doors, and it's a new process that you haven't done before and optimized.
-Extra time to mount electrical boxes.
-Is the increased R value really worth it? Compare it to better air sealing, more insulation in the attic, or better windows and I'm not so sure it's the best allocation of time and money unless you're in a really extreme climate.