Insulation for Irregular Walls
diy_buck
| Posted in General Questions on
I’m renovating a room and have the exterior wall down to the 2×4 studs. Unfortunately the house was built in an…interesting…fashion and the room has gone through remodeling before, so there is uneven spacing of studs (some up to 24″ OC but some with spaces down to 6-8″), extra holes and notches from previous wiring, etc.
I pulled out poorly installed FG batts which were clearly not doing a very good job based on how dirty they were, sagging, being shoved in small spaces, etc. I was thinking of using foam board, which I’ve used in the past and liked. I was looking at the foil faced stuff which is listed as having a slightly higher R value than non-foil. Since there is Romex running through the walls, I can probably slide 1″ or 1.5″ foam behind the wires then either double that up or use 2″ above and below the Romex. I would finish with spray foaming all the seams and where they hit the studs (also sealing the bottom and top plate before installing the foam).
Then I saw someone mention blown in insulation which is good for filling in irregular spaces. I read one guide which recommended putting a layer of foam board over the entire wall, but I’d prefer not to have to do this and change the depth of the electric boxes and door and window trims. Can I just install plastic sheeting across the entire wall and then blow in through that? Would that provide a better R value?
I also read about wet cellulose but sounds like that’s less easy to DIY.
Thanks for the help and all the great info around here!
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Replies
I did a bunch of randomly spaced studs in my attic with rockwool bats. Bought a mix of 23" and 15" wide. Trimmed or stuffed and cut slits for wires as necessary with a bread knife.
Not much learning curve, turned out looking great. Made a huge difference in the room.
I have done the same as Jeff. It works well. Blown-in can also work. There is a special fabric that goes on the wall that you blow through. Could also use wet cellulose. If it is like one 12' wall, go with the rockwool. The other methods are more involved. Buy the fabric, rent a blower, get the cellulose, clean up the mess. Wet cellulose is a contractor job. Rockwool is low mess, work at your own pace. I use it all the time to fix my house with great success.
Thanks for the tips! Wall is about 25' with one window and a sliding glass door so might be easier to go with Rockwool. No 24" batts are available at my local stores but hopefully I can order some of those. The blown in looks nice but I'm just picturing getting the machine home, having the wife dump in cellulose while I'm trying to get the hose in the right place, etc.
Are there any different types of Rockwool? They are labeled as fire and sound proof but also offer good insulating effects also?
Thanks again!
What I used was labeled as R-15 insulation for exterior walls. Unfaced batts. Rockwool brand in my case, but there are others.
You don't want the rigid panels for this, but they seem to be pretty hard to buy retail.
Thanks, I think I found the correct thing:
https://www.homedepot.com/p/ROCKWOOL-R-15-Comfortbatt-3-1-2-in-x-15-in-x-47-in-Fire-Resistant-Stone-Wool-Insulation-Batt-59-7-sqft-RXCB351525/202090820?source=shoppingads&locale=en-US&pla&mtc=Shopping-CM-F_D29A-G-D29A-Multi-Multi-NA-Feed-PLA_LIA-NA-NA-MinorAppl_Special_Buys&cm_mmc=Shopping-CM-F_D29A-G-D29A-Multi-Multi-NA-Feed-PLA_LIA-NA-NA-MinorAppl_Special_Buys-71700000042813121-58700005464629311-92700067963002094&gclid=EAIaIQobChMIgsHnm6zu9QIVCuOzCh3Llg3CEAQYASABEgI8R_D_BwE&gclsrc=aw.ds
Yes, that's exactly what I used.
Also wanted to double check about a vapor barrier. It looks like I am in zone 4A. When I looked up the building code it says:
"Class I vapor retarders shall not be provided on the interior side of frame walls in Zones 3 and 4."
So no plastic sheeting, but should I be using something like a Class II or III vapor retarder? Can't really tell the way it's written (just says not to use Class I). Would that be Tyvek or something similar or just drywall and paint? Thanks!
The fire and sound is thinner than the other type. You want the thick stuff. Order it if you need. You might check around for an insulation material supply house. Also, just cut the batts with a 24" length and install sideways. Just stack them up.
Just a thought, is there a state energy saving program that would do this for you?
Thanks, that's a good idea about stacking them up, then I don't have to worry about "ripping" any the long way. I know with fiberglass they say you shouldn't push it into place since it will compress. Is the Rockwool a little easier where I can just shove the pieces tight together?
Good idea about the energy program, I'll check it out!
You want it cut to be about 3/4 inch wider than the stud bay, so you get a press fit and it stays in place well. And, yea, you shove the prices up tight against each other.
It's forgiving within half an inch or so.
If it's too tight it'll start to bow out or buckle, and you can pull it out and trim a bit.
The consistency is similar to a loaf of bread.
Rockw0ol is a great DIY material. Cut it with a Rockwool knife if they have them, or a serrated bread knife (same thing), and cut it 1/4- 1/2” bigger than you need. You can fit together smaller pieces easily; you’ll get the hang of it quickly. I built a small plywood table with a 2x4 “fence”which is very helpful. Material comes in 4’ lengths.