I live in Western New York. My house was built in 1920. I gutted the spare bedroom and removed the plaster and lath. From the inside to the outside I have 2×4 studs, 3/4” shiplap, esbestos siding with cedar board siding on top. There was no insulation in the wall cavities as I’m sure you have guessed by now.
How should I go about insulating the wall cavities in my particular situation? Do I need an air gap? What kind of insulation would be best in my situation? Is there anything I want to avoid doing? I’m reading allot of conflicting stuff on the web and no two situations are the exact same. I’ve considered not insulating but I’d prefer to since there is a water pipe not far from this exterior wall that freezes about once a year when it gets into the single digits and I figure insulation might solve that. Thanks.
Replies
Your best solution would be to have foam sprayed into the wall cavities. But a decent alternative would be to install ROXUL (now Rockwool) insulation. I think you'll need a vapor barrier in your area over the ROXUL. I prefer ROXUL over fiberglass because its more forgiving to install. If you don't cut it perfectly, you can just stuff some loose ROXUL into any gaps, and its just fine.
Thanks for the response. I would definitely need a vapor barrier on the inside facing side of the roxul. before I put up drywall.
My concern is all the stuff I have been reading about how insulating older homes reduces air movement in the cavities, which doesn't allow the wood to dry, causing rot/mold/ect...
Is this a valid concern?
I second the Roxul recommendation. It's also fire resistant, can get wet and dry out without impact to the R rating and unlike fiberglass the little critters dont like it much. However you should think twice about the vapor barrier. You dont need it and it will prevent the insulation from drying out if it ever gets wet.
Now I've been researching vapor barriers and it's all conflicting information about that too. Great. I am kind of leaning towards no vapor barrier and rockwool now.
You say it would prevent the rockwool from drying if it gets wet. I would assume you are referring to a plumbing disaster or something weather related...something other than vapor movement from inside the house. How would having a vapor barrier between the drywall and rockwool prevent it from drying? I feel like in either case, if it were to dry, it would have to dry to the outside of the house since the drywall will be sealed up so well, even without a vapor barrier. Will insulation dry through the drywall?
You don't need a vapor retarder for the wall assembly to work, you just need to control air movement. If moisture in the wall is a real concern you can always accomplish both tasks by using a "smart" vapor retarder such as Intello or Membrain and caulk along the seams and edges. If you don't go with a vapor retarder or smart retarder you could also control air leakage by following an airtight drywall approach. We have articles and videos on that topic here on the site. And yes, as long as you aren't installing vinyl wallpaper or some vapor barrier paint your wall will allow for some drying to the inside.
As for insulation, mineral wool is great, but cellulose and fiberglass would also work just fine. Once you're controlling air movement the type of insulation becomes much less critical, assuming you are installing each correctly.
By the way, for that pipe in the exterior wall you might consider putting a piece of rigid foam between it and the exterior sheathing and caulking/foaming it in place for some added R-value there. If you can't fit rigid foam, canned foam is a good second choice.
Justin
Fine Homebuilding
Something that I encountered in a 1918 house that I wanted to insulate: knob and tube wiring. This has to be replaced before you insulate because the wires rely upon the air gap within the uninsulated wall for cooling and electrical insulation. The original rubber insulation is way beyond life span. Plus the knob and tube positive/neutral wires were run a certain distance apart