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skinny2 11-13-2008 11:09 AM

Crawl Space Insulation
 
I have a mid-1800's home built with stone foundation and logs for floor joists. Located in Ohio so heat is larger concern. About 60% of the house is crawl space, about 2' from the ground. The space gets very cold because the stone foundation lets a lot of air through. There is insulation in the floor joists for parts of the crawl space, but the Kraft is facing the ground. It looks like it's drawn moisture.....some of the Kraft has black on it (mold?), and parts are falling down.

It's going to be a nice weekend for army crawling and I was thinking about doing some improvements under there. One thing I've wanted to do is put down plastic on the ground. I also considered continuing the plastic up the stone foundation and attaching to the sill. This would help with drafts coming into the crawl space but I'm worried about humidity/moisture. I will likely do the plastic first just to make a cleaner area to crawl around. The dirt floor is very fine powder and it makes a terrible mess and very dusty. So in terms of the ground, there's not really any moisture problems to speak of. Any thoughts on this?

Also, do you think I could just flip most of the insulation over so the Kraft is against the floor? Or should I throw it out and buy new (trying to keep this on the cheap). The logs are very different sizes and shapes so I don't think sheets of styrofoam would work very well.

Rkeytek 11-13-2008 02:50 PM

I would go with new insulation (the r values are probably higher than what you have in there) with the paper side down, then roll a 6 mil plastic vapor barrier over it and attach that to the beams

Wildie 11-13-2008 04:29 PM

The rule for vapor barrier is that its installed on the warm side!
Otherwise, moisture laden air will condense on the plastic and cause mold problems.

DangerMouse 11-13-2008 04:54 PM

if there are drafts, i'd address that before VB. take a tube of caulk or a can of Great Stuff foam with you under there to seal cracks first.
(smoke a cigarette or use 'other' smoke methods under there to see where the drafts are.) =o)

DM

Maintenance 6 11-14-2008 06:21 AM

Plastic on the ground is an OK idea, but I'd stay away from the walls. That would seal up the space and cause moisture issues. Plastic on the ground will keep a lot of additional moisture from evaporating into the air in the space. Crawlspaces need to breath. Install your new insulation with the vapor retarder up against the warm floor. You want to keep the warm vapor in the heated side, not on the cold side where it can condense in the insulation. You have mold now because the vapor retarder is on the wrong side of the system.

Marvin Gardens 11-14-2008 11:19 AM

Quote:

Originally Posted by Maintenance 6 (Post 184718)
Plastic on the ground is an OK idea, but I'd stay away from the walls. That would seal up the space and cause moisture issues. Plastic on the ground will keep a lot of additional moisture from evaporating into the air in the space. Crawlspaces need to breath. Install your new insulation with the vapor retarder up against the warm floor. You want to keep the warm vapor in the heated side, not on the cold side where it can condense in the insulation. You have mold now because the vapor retarder is on the wrong side of the system.

Exactly.

Unheated spaces up against heated spaces need to breath to get rid of excessive moisture.

gomi_otaku 11-28-2008 01:07 PM

This is information I was looking for to confirm what I knew- that the faced insulation goes toward the heated area.
However, does the kraft facing allow one-way moisture transfer? because if it doesn't, then it would still cause condensation, wouldn't it? In this case, the moisture is forming on the "faced" side, since it is facing the unheated "moist" space- but if you flipped it, and the facing doesn't "breathe", wouldn't the moisture just build up on the other side of the facing, INSIDE the batts of insulation?
gomi_

Maintenance 6 11-30-2008 03:37 PM

No because the vapor retarder will then be against the heated floor and will be above dew point. No moisture will be able to condense on it. Right now your vapor retarder is in the cold where it the temperature drops below dew point and moisture condenses. Vapor pressure always passes from warm to cool because warm air can hold more water vapor than cool air.

gomi_otaku 11-30-2008 07:37 PM

That makes sense. Funny thing, I was just at Home Depot today. Their insulation aisle has production panels lining the aisles that depict how to select insulation, and for what area and purpose. Their explanation of faced and unfaced insulation- faced insulation is to PREVENT moisture from penetrating into the house envelope FROM OUTSIDE!! I beleive you can probably go into any HD in the nation and see these same displays mounted on the aisle racking.
gomi_

Maintenance 6 12-09-2008 10:17 AM

In areas where you run air conditioning all year around and keep the indoor temperature lower than the outside, then that would be true. Then you would install the vapor retarder toward the outside. There is only a small slice of the U.S. south where that applies. When it comes to the big box stores, only trust them to sell you the stuff, not to tell you what to use or how to apply it.

sawyerEd 12-12-2008 11:36 AM

Moisture Problems
 
Gomi, you are in Seattle, skinny is in Ohio and has different environmental conditions than you. Skinny's outside air is relatively dry in the winter and moist in the summer so his vapor travel reverses through the kraft paper during the year. You are moist outside basically all year depending on your elevation and proximity to water. Skinny needs to poly his dirt floor, fill cracks that are leaking water into his crawlspace and provide some heat and air exchange in there. His logs have lasted as long as they have because they have almost free exchange of air through the rock foundation and that has kept the logs dry enough to impede the growth of mildew and rot. By adding insulation he has caused condensation points to form against the backwards paper and in his log joists, no more free air exchange. If he wants to save this building and have warm floors he is looking at a major retrofit of his foundation or insulate the topside of his floor if he can spare the headroom.


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