[xiph0s]

hopefully I'm in the right spot. I recently purchased an old house and gutted the entire thing. The house has completely new blown in insulation in the walls and new batt insulation in the attic and the crawl space. This house is so old that the floors in two of the rooms have no subfloor. Meaning, we have plank pine floors laid directly onto the joists. During the renovation new insulation with a kraft face was put in the crawl space (kraft paper towards floor) While standing on the floor mentioned above I can feel air still moving into the house.

My question is this. I do not want to put up styro board due to cost and hassle of putting it up (crawl space is tiny) but something needs to be added to control air movement and heat loss. Would it do any good to take some standard fiberglass insulation without kraft paper and run it perpendicular to my joists so that in effect I have insulation between the joists and then the new layer of insulation covering everything including the joists and old insulation. If I were to do this I would use a thinner, lower R-value insulation and staple it to the joists as I worked my way across the house.

My main concern is moisture being trapped in the insulation. Since I am not familiar with insulation I must also ask does fiberglass insulation allow moisture to migrate out of it?

The crawl space already has a vapor barrier and vents are insulated as well.

thanks in advance!

[21boat]

serious question here Why is it always a cost thing on doing the best insulation possible as opposed to it being there for life and heating the building for life? Where is the savings there?
Adding more unfaced insul stapled to the joist knocks down the 'R' value in that because of it being compressed. One place the air gets is is where the joist meet that outside band and plate. Stuff spray foam seals that up well. The ides for moisture in the fiberglass id not to be in it at all. It has to breath so as not to trap moisture CREATED by improper vapor barrier or double barrier. A perfect glass insul in a crawl space can go bad if the crawl space air itself gets to high in moisture .
The reason I say that is because fiberglass insulation in a crawl space is not the best way simply because of no cross ventilation and if it has cross ventilation possibly the bugs mice etc can get in through screens. Hears the catch. Any foam board in a crawl space should be put right under the sub floor. The you can add unfaced glass insul to that to secure that from dropping out. Use a treated lath to help support the glass and it will breath under the crawl space. You don't want to use a foam board under the glass insul to start a double vapor barrier problem. 5% of any moisture in glass kill 95% of its insul properties. Spray foam is the perfect insulation to use and you will NEVER have a draft. Spray foam also is mold resistant and has higher "R" value per inch than glass and the bugs stay out. If this is not a huge crawl space you can do your own spray foam I posted a site below for that. Reuse the insul there peel of the kraft face and recycle it to the attic on top of the other insulation. I don't know if the crawl space has cross ventilation in it which changes this here also except for the spray foam part.

http://www.southface.org/web/resourc...e%2000-774.pdf

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