Hi All,
I live in Rochester, NY. The attic in my old (1850) housewith aluminum siding has no insulation. I’ve just spent 2 days air-sealing all the openings I could find up there with foam per Fine Homebuilding’s excellent book on insulation by Bruce Harley. What a difference that alone has made! Our second floor is definitely warmer.
My question is this now that I’m ready to insulate: If I blow cellulose in the open attic floor, and in the stud bays that are open at the gable ends down to the 1st floor ceiling, do I need vapor barriers? Of course there’s no way I can put vapor barriers in the stud bays, my main dsire is to not do anything that might cause problems with moisture in the walls. Currently, the 2 house bathrooms and stove hood are vented to the outside so I know I’m not adding a ton of moisture that way.
What do you think? Can I just blow the cells in?
Thanks in advance,
Dave
Replies
One reason why moisture was not as much of a problem in older (roughly pre-1955) homes is that they were typically solid plaster walls painted with oil paint, and the walls would get to several coats over a few decades. This made an excellent vapor barrier. The early latex paints that later became popular were not nearly as good at preventing moisture transpiration, especially over drywall.
If your house has reasonably crack-free plaster, and the expected number of coats of paint for a house its age, that's a pretty good vapor barrier. The only addition you need (and one that you've been working on) is to seal any air leaks around fixtures and pipes and along the tops of studwalls.
For any new drywall work or plaster repair, if you don't put poly behind it, use a primer or paint that has a vapor barrier rating. Most current good-quality paints will suffice, but check the label.
I thought the older houses didn't have much problem with moisture was because they were so leaky and dried out as fast as they got wet....
Yeah, that's another reason.
"If I blow cellulose in the open attic floor, and in the stud bays that are open at the gable ends down to the 1st floor ceiling, do I need vapor barriers?"
Vapor barriers are overrated. Most moisture enters wall cavities (or attic spaces) riding on leaking air. Seal the air leaks to solve the problem. Blow the stud bays using dense pack technique, then cap them off with blocking for good measure.
Dave,
"The 2 house bathrooms and stove hood are vented to the outside so I know I'm not adding a ton of moisture that way."
What about the crawlspace/basement??
You can get a lot of moisture from down there.
Rich Beckman
Another day, another tool.
Rich, You're absolutely right about basements and crawlspaces. I did a bunch of grading and running downspouts into drain pipe network away from the house ( the basement was wet in spots before). I'll know for sure this spring when the snow melts!
Yes, you can just blow the cellulose in.
Unlike batt insulation, Cellulose, installed properly, is not an effective medium for air to move back and forth through. You don't need a vapor barrier with cellulose although I would use a vapor barrier paint, or an oil based paint as a precaution in a high humidity area like a bathroom.
Be Constructive
Gord
St.Margaret's Bay NS