Under floor insulation--

Thurman · 11-07-2010, 07:24 PM

Kraft paper facing: Up or Down? Stopped by a friends house to day who has recently put a new room on the back of his home. He had been putting fiberglass Kraft paper faced insulation under the new flooring yesterday and today. He was complaining about having to lie on his back in order to staple the paper strips on the side to the floor joist. Hmm, I had to ask him why he didn't put the paper to the floor side. He just replied "How would I staple it in though?" Now I have been taught to put the paper to the "home/interior" side of whatever I was putting insulation on. I have been taught to use the straight wire "hangers" to hold the insulation up under a floor, spacing them even closer that the manufacturers recommendations. So-which way do you put under floor, fiberglass, faced insulation? David

wnabcptrNH · 11-07-2010, 07:26 PM

paper facing down into the room. you fold the paper edges out and they staple onto the ceiling/floor joists above.

Thurman · 11-07-2010, 08:37 PM

"paper facing down into the room." A bit confusing there. But I failed to mention this is within the crawlspace under a single floor home. The paper would be facing the dirt this way. I'm thinking the paper should be facing the bottom of the floor to act as a vapor barrier, much as the insulation of a wall faces the living space. Thanks for the response. Doing something the same way many times does not always make it the right way, that's why I'm asking. David

wnabcptrNH · 11-07-2010, 09:07 PM

Well if you are putting in insulation in the crawl space I wouldnt be using any insulation with paper backing.

FYI paper is not a vapor barrier so its honestly usless at that point. You need to install a 6 mil poly vapor barrier on the warm side of the insulation.

If it were me, I would have a company come in and spray foam that area because you get insulation and vapor barrier with the closed cell type.

**Gary in WA** · 11-08-2010, 12:55 AM

Unless required by Code: “Crawlspaces should be designed and constructed as mini-basements. Crawlspaces should not be vented to the exterior (see FAQ on Crawlspace Venting). They should have their floors uninsulated, the ground vapor sealed, their walls insulated and air sealed, and their air conditioned with indoor air.

Crawlspaces should have a continuous sealed groundcover of vapor diffusion resistant materials, such as taped polyethylene or, preferably, a thin poured concrete slab over polyethylene with perimeter and control joints sealed.” From: http://www.buildingscience.com/docum...d%20in%20walls

If vented, vapor retarder faces the conditioned living space above, never a vapor barrier.

Gary

Thurman · 11-08-2010, 01:23 PM

Thanks a bunch for all the information. Now I can take this printed info back to my friend and tell him to tear it all out and start over again.

. Lesson learned here. David

Jim F · 11-08-2010, 10:38 PM

My crawlspace is vented and has 6 mil covering the ground and going partway up the CB wall. Under the floor it has 4 inches of rigid foam that is flush with the floor joists and held in place with what looks like 1x3 tongue and groove finished floor boards. Not sure why they used those to hold the insulation but it seem to work OK.

operagost · 11-09-2010, 01:20 PM

Atlanta's just barely within the zone in which the vapor barrier should be placed toward the living space. In the southernmost part, cooling is used far more than heating so the opposite is true. This is probably why you have been told to place the paper (which is a lousy vapor barrier, but I digress) toward the living space: because that's how it's done in the southern 1/3 of Georgia.

http://www.energysavers.gov/your_hom.../mytopic=11810