Vapor barrier in middle of insulation?
I have a 1893 balloon framed home in Wisconsin. It has 6″ of blown cellulose in the attic floor between the plaster and the T&G. I believe this is approx R24. I would like to double this by putting 8″ FG bats on top of the T&G. There currently is no vapor barrier. I am considering putting poly on the floor before the FG bats. I have foamed all the pipes, wiring, etc. to try to air seal the attic. After doing this I looked at the T&G floor and thought it probably is an air sieve.
My goal is to reduce moisture infiltration into the attic and provide more R value to my home. Any recomendations?
Thanks for the recomendation on the foam gun. This thing is extremely handy. Although I still have not figured out how to make a sanwich. Maybe with more experience.
Replies
Your vapour barrier should not be any further than 1/3 from the warm side. What you are proposing is 1/2. So if you can have R48 on the cold side it would be fine but do you really need all that insulation.
Tom
What are the signs you are getting moisture into the attic? What is it doing?
If moisture is truly now getting up there, you definitely don't want to stop it halfway and ruin all the insulation below it.
Excellence is its own reward!
The only moisture problem I see is the nail points through the roof boards turn white in the winter from condensation. My concern is my attic never had any venting until two summers ago when I replaced the standing seam metal roof with conventional shingles. We added 4 pods but the attic does not have soffit vents. However the soffits are T&G and daylight can be seen through them from the attic. To make up for the lack of venting I want to air seal it from the warm living space as much as possible. In Wisconsin I believe code for a new home roof is R48. Maybe thats overkill.
Some of the northern states do have high requirements in new work. Once you start getting over R30 the payback can take longer. You can seal agianst moisture into the attic with paints in the ceiling. Don't trap moisture by putting plastic over the insulation tho' I can think of two jobs wheree owners did this and had to remove all the insulation because of the mold farm they created. If you have no major signs of moisture in attic, either you aren't getting that much or it is venting itself automatically through holes you are unawares of ..
Excellence is its own reward!