--70.158.xxx.xx

you want roxul which is now rebranded as rockwool. The comfortbatt is their insulation product the 2x4 for 24" spacing has r15. It's great stuff. My lowes shows I can order it for availability in 2 weeks. $53 gets you a bag of 8 pieces 4' long. I use an old serrated knife to cut it, but any sharp long knife will do. --24.194.xxx.xxx

You could do as Robert, Ontario does and use the spray foam insulation as it fills in all cracks and voids and is not susceptible to mold. It is more expensive though. --73.120.xx.xxx

--71.184.xxx.xx

Yep, rockwool. The bat is actually 23" wide to account for the width of a 2x4 24" on center so don't let that fool you. It is more expensive than the older paper faced fiberglass bat but it will meet the R15 code requirement where the fiberglass can only reach R13 in a standard 2x4 stud-bay. It's pretty easy to work with, cut with a long knife, and then stuff it in a bay. No stapling or taping required, it stays in the bay through the slight compression against the side studs. For the odd pieces just cut off a chunk or stuff the loose pieces into the holes. It's also less of a skin irritant than the old fiberglass which makes it less painful to install. --64.130.xx.xx

I get mine at Menards, it is regular stuff for them. HD may have it but the 11 percent has been influencing my buying choices. --76.188.xxx.xxx

Sorry, I hit send too quickly, you can make a vapor barrier by stapling visquene to cover the interior before drywall is attached. --76.188.xxx.xxx

I would not tape together insulation, I'd find some the proper width. The other option would be to use unfaced and then add a vapor barrier stapled to the insides of the studs. You could partially install the vapor barrier first, maybe up 3' or so, then lower the unfaced batts in, then staple the next 3' or so, etc. --99.92.xxx.xxx

DJ, you will still want a mask and perhaps long sleeves if you are working w/ roxul for any length of time. --24.194.xxx.xxx

FYI even with 24" oc framing about 12% of the wall is lumber which has a very low R value compared to the parts that have insulation. Using R15 insulation in the stud cavities only means that that part of the wall is R15 while the parts taken up by framing are a bit more then R4. Adding even a 1/2" layer of High R insulation board almost doubles the R value where the framing such as 2x's,& headers & rim joists are. --71.184.xxx.xx

Thanks for clarifying. I've never seen that done...seems like you'd have to remount or extend electrical outlets and switches too, but if the wall is opened up that would be fairly easy. --99.92.xxx.xxx

//www.homedepot.com/s/electrical%2520box%2520extenders?NCNI-5 --71.184.xxx.xx

Fiberglass insulation is the worse insulation where after period of time air pockets develop where the R value drops. Roxul or spray foam does not deteriorate with age. More expensive upfront but worthwhile. Spray foam can be bought in 2 container DIY or consider Roxul rock wool which is fire proof along with does not become moldy like fiberglass. Every time a wall in the house is broken out then when the fiberglass insulation is removed there is black mold where if insulation has water content then heat transfer increases. Roxul then a vapour barrier then sealed air tight with tape. View a few different videos on You Tube about insulation. --99.236.xxx.xxx