Insulating Gaps in Between Framing Studs with Spray Foam vs Rockwool
WilliamC
| Posted in General Questions on
In remodeling the exterior of my house, I have noticed that there are a few areas typically around windows and door, where there are two studs within about an inch of each other. Should I try to stuff rockwool into these gaps or simply fill them with canned spray foam? I have tried getting rockwool in them and it’s pretty difficult to do without compressing it quite a bite which compromises its R value. I can fill these gaps much quicker with spray foam. Are there any issues with filling these gaps with spray foam?
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Search and download construction details
Replies
William C,
IMO the foam will be faster and probably a bit more effective. Cramming rockwool in will be tedious and lumpy as you have already found. The R value differences would be largely moot as the studs will degrade either choice. These small framing gaps are like the super charged example of center of wall R value being degraded by framing R value.
While you are at it, look to seal any air leaks from sheathing gaps. Sealing these will produce more useful heat loss control. The penetration points of the cable and pipe in your photo are good examples of why I don't like plastic sheeting as a vapor control. If you can tape up these gaps with Tyvek tape it might help slow a hidden moisture condition in the future.
Thank you for the helpful response. Spray foam definitely seems like the best way forward. I just wasn’t sure.
The picture here was taken from the outside. So that’s plastic on drywall. I am re-sheathing with zip. So there shouldn’t be any air leaks once the zip is up and taped.
I am also taking as much of that plastic out as I can since I don’t want a vapor barrier on the drywall especially after the zip and foam CI are installed. I’m also in CZ 4a so I don’t believe a vapor barrier in the drywall is a good idea. Not sure why they put that there when it was built.
Unless you are attempting to use your insulation as the air control layer, they will perform so similarly that it would be hard to measure. Spray foam is faster. Mineral wool has somewhat lower levels of up-front carbon emissions and is friendlier to future repairs or renovations. Spray foam will cost a lot more for the volume needed. Installing either without a respirator is bad for your health but the spray foam is probably worse for your health. If the framing is below about 50°F it won't cure properly.
Thank you Michael. There are not many of these areas. They could probably all be done with two cans of Great Stuff.
I wasn’t aware that one should wear a respirator with canned spray foam. I have been with the rockwool.