Building out 2×4 Walls for Additional Insulation
Hello – I am in the midst of a remodel of a century home in the northeast. The building is down to the studs and was framed with 2×4 lumber. In the past, given a similar situation, I’ve taken 2x4s and ripped them down the middle then nailed them to the face of the existing framing, allowing me to get R23 mineral wool batts in.
In thinking about this project I want to reduce the thermal bridging if possible. I still want to build out to get R23, but instead of running additional lumber the full length of the framing, I am considering just using blocks every eight to ten inches and then attaching horizontal furring strips to make the drywall crew’s job easier.
Is this going to provide any additional upside, aside from reducing the amount of lumber I’m purchasing?
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Replies
If you'll also be doing a reside, and will have access to the exterior side of the studs too, adding 1.5" polyiso on the exterior will get you R9 of exterior continuous insulation which will give you R23, but a much better performing R23 than you'd get with batts alone.
I don't really see a problem with your proposed "blocks and strapping" arrangement, but I think there will be a lot of extra labor for the insulator to cut around everything. Dense pack cellulose might be a better option here since it would fill all the oddball voids between framing members, so that might be something to consider. I'd put in a smart vapor retarder behind the drywall for a little extra insurance too.
Note that you can put rigid foam on the interior side too, although that's much less commonly done. If you try this, you want to make sure your wall can dry to the exterior.
Bill
Thanks for the reply. Exterior insulation isn't in the cards for this property for the foreseeable future - hence my desire to get as good of a wall assembly on the interior as I can. I'll be doing all the work myself and don't mind the cutting, but blown cellulose isn't a bad suggestion. I'd rather stay away from rigid foam on the interior in case I am able to justify residing it in the future.
In New England is is normal to strap ceilings this way with 1x3, I've seen it occasionally on walls too. I've heard people say it's code in MA but I can't confirm. It makes the drywall go up a lot easier. The strapping evens out any minor irregularities in the framing, and if there are grievous gaps it's easier to shim a furring strip than to try and shim behind drywall. The drywall guy has a target to hit with the screws that's twice as big. And this probably isn't an issue with walls but on ceilings the strapping is a great thing to hang onto when you're up on a stepladder and need to reach a bit.
In New England it's totally normal to run wiring and even 1/2" copper and pex plumbing between the drywall and the ceiling joists, which I always thought was a little sketchy although it does keep the pipes on the warm side of the wall. But if you're blocking with pieces of 2x the faces of the studs will b 2-3/4" back from the drywall which is well-protected.
I second the idea of blown cellulose.
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sscogin,
Two other options you might consider:
If you are thinking of cellulose, I'd use a Mooney wall.
If you prefer to use batts, maybe a Bonfiglioli wall.
Thanks for the reply! The Bonfiglioli wall seems like the right fit for this job / me.
My first thought was the Bonfiglioli wall but Malcolm beat me to it. The advantage is that somebody else has already proven that it’s doable in the real world and has worked out all the kinks. Here is an article describing it.
https://www.finehomebuilding.com/project-guides/insulation/breaking-the-thermal-bridge
Since you’re not doing exterior insulation or re-siding, a second 2x4 wall could be added inside for a double stud wall, but you’ll lose some living space which may matter if it’s a smaller house (as many older homes are.)
Edit: Assuming that you will use the drywall as an air barrier for your blocking idea, you would need to completely build out the perimeter of all walls and openings so that you have something to seal the drywall to. Adding a second stud wall may be a less fussy solution.