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Moisture in crawlspace?

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Topic by bringitonhome posted 03-31-2010 09:12 PM 3507 views 0 times favorited 6 replies Add to Favorites Watch
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bringitonhome

5 posts in 4521 days

03-31-2010 09:12 PM

Hi-
I’m planning on remodeling a room in my house that is over a crawlspace. For some reason, the it’s split into two areas by a foundation wall (for support?). On one side, there is fiberglass insulation between the ground floor joists that is falling down – i’m assuming that’s becasue of moisture. There’s no insulation on the other side – maybe it had already fallen and the previous owner removed it.
As I remodel the room above, is there anything I should do to address this moisture issue? Is it even an issue? Are you not supposed to use insulation in a crawl space because of the humidity? Must I insulate the floor at all?

The floor of the crawlspace is a sandy/dirt mix. and is at or near ground level.

Thanks.



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Dan Lyke

331 posts in 5248 days

04-01-2010 02:10 AM

I did a heck of a lot of reading on this and didn’t come up with anything definitive, but my big project last summer was insulating and putting a vapor barrier in my crawl space based on what I felt the preponderance of the evidence was.

First thing: Fiberglass insulation falls down because it wasn’t secured properly, not because it’s humid. It should be paper side up (if it’s faced), and held in place with metal springs or by a stapled netting, or other mechanical fixing.

I then also put down a vapor barrier on the ground. 2 layers of 6 mil plastic (places that do this professionally will offer you thicker stuff), taped at the seams and glued to the foundation and piers with construction adhesive.

Subjectively this has made a huge difference in the house, the house is warmer, we no longer have problems with mold on the walls in the rainy season, I highly recommend it.

-- Dan Lyke, Petaluma California, http://www.flutterby.net/

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bringitonhome

5 posts in 4521 days

04-02-2010 05:32 PM

thanks for the reply.
Did you just use a regular 6mil painting dropcloth? or is there some special “vapor barrier”?
Also – did you insulate the foundation walls with that foam block stuff? Or just the floor above? I’m going to be running some plumbing in one of the areas, so I may have to insulate the walls. Wondering if that would go outside or inside the vapor barrier. I’m guessing inside…

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Dan Lyke

331 posts in 5248 days

04-02-2010 05:49 PM

I bought a big hundred foot roll of the stuff when Yardbirds was going out of business, but, yeah, same stuff. 6 mil clear polyethylene.

I just did the floor above, and I wasn’t confident enough in my vapor barrier to try to seal off the vents and other ways air could get through the foundation. For my new workshop I think I’m going to go with a sealed crawlspace, as the EPA and various other government agencies now seem to recommend, but as a retrofit for my existing house it seemed like more than I was up for.

But I also live in a very mild climate, we have the rainy season and the dry season, and frost 5-10 days a year. So the main thing was controlling the humidity and some basic insulation during the dry season.

-- Dan Lyke, Petaluma California, http://www.flutterby.net/

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UnionLabel

70 posts in 4605 days

04-21-2010 06:26 PM

bringitonhome, I know I am a little late on this, but here is the rule of thumb for crawlspaces. There is the vented and unvented crawlspace, not sure which you have, so here is both.

How to Insulate a Vented Crawl Space
The insulation is installed from below, much as it is installed in ceilings.

1. Cover the ground with sheets of six-mil plastic film. The sheets should overlap each other by approximately twelve inches, and extend a few inches up the walls.
2. Tape the film in place at the walls and hold the seams in place with tape, scrap lumber, or rocks. After the ground is covered, you’re ready to install the insulation.
3. Fit the insulation batts into the joists with the Kraft-paper vapor retarder facing against the sub-floor. Make sure the insulation fits snugly so that there is no air space between the flooring and the insulation.
4. Staple the insulation flanges securely to the sides or bottom of the joists (called “inset stapling”).

When installing Kraft-faced insulation, use wire lacing, screen or stiff wire fasteners to hold the insulation firmly in place. The fasteners are bowed upwards into the insulation, pressing it gently against the sub-floor without overly compressing it. Place the fasteners at least six inches from the end of each batt, and no more than 24 inches apart.

How to Insulate an Unvented Crawl Space

In an unvented crawl space, the general rule is to insulate the perimeter walls. This eliminates the need to separately insulate the water pipes and heating ducts.

1. Cover the ground with sheets of six-mil plastic film. The sheets should overlap each other by approximately twelve inches, and extend a few inches up the walls.
2. Tape the film in place at the walls and hold the seams in place with tape, scrap lumber, or rocks. After the ground is covered, you’re ready to install the insulation.
3. Locate the header joists, which run across the ends of the floor joists. Measure and cut pieces of unfaced insulation and place them against the header joists between each floor joist. Completely fill the spaces enclosed by the sub-floor, sill, and floor joists.
4. Install lengths of standard batts or the wider basement blanket insulation to the sill using furring strips to nail the insulation to the edge of the sill plate. The insulation should be cut long enough to hang down the wall and extend two feet into the crawl space. It can also be installed horizontally in the same manner.
5. Anchor the insulation as close as possible to the wall where it meets the ground using 2×4s.
6. Locate the stringer joists, which run parallel to floor joists. Position an insulation blanket against the underside of the sub-floor and staple or nail it directly to the stringer joist. Or, attach the blanket to the top of the sill, and wedge smaller pieces between the sill plate and sub-floor. (This technique takes longer, but provides better thermal protection at the joist.) The insulation should be cut long enough to hang down the wall and extend two feet into the crawl space. It can also be installed horizontally in the same manner.
7. Anchor the insulation as close as possible to the wall where it meets the ground using 2×4s.
8. Make sure all pieces of insulation are tightly butted together. Be sure they fit snugly, without gaps between them. Taping is not usually necessary. An alternate way of fastening basement blankets to the walls in crawl spaces is using a Hilti-type gun to drive the fasteners into the concrete.

-- Methods are many,Principles are few.Methods change often,Principles never do.

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englederek

2 posts in 4204 days

02-11-2011 10:05 PM

The most informative website that i have found on this topic is http://crawlspaceinfo.com

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rrdesigns

100 posts in 4651 days

02-12-2011 06:07 PM

Good detailed advice. Thanks for sharing your expertise.

-- Beth, Oklahoma, Rambling Road Designs

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