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Patton

Insulation for Crawlspace

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Is it required for there to be insulation in a crawlspace? I’m selling my old house, and I am going to get the crawlspace treated. They want to rip out the insulation; I believe it has caused moisture issues inside the house anyway. I am just trying to budget if I need to replace the insulation.

Edited by Patton

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If the house has central heat and air, with duct work under the floors, leaving the insulation off is the easiest solution.  Modern theory is to include the crawlspace as part of the conditioned area of the house, as such the outer walls are often insulated with rigid insulation, not fiberglass batts.  They will typically put some sort of vapor barrier under the floors to guard against moisture. In older homes, this isn't practical, so the next best solution is a properly vented crawlspace with no subfloor insulation.  This will prevent moisture accumulation such as you described.

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7 hours ago, No_0ne said:

If the house has central heat and air, with duct work under the floors, leaving the insulation off is the easiest solution.  Modern theory is to include the crawlspace as part of the conditioned area of the house, as such the outer walls are often insulated with rigid insulation, not fiberglass batts.  They will typically put some sort of vapor barrier under the floors to guard against moisture. In older homes, this isn't practical, so the next best solution is a properly vented crawlspace with no subfloor insulation.  This will prevent moisture accumulation such as you described.

I have heard others say that too.  I appreciate it. The moisture in the crawlspace really isn’t bad but some of our closets would get mildew. Someone hinted that the insulation could be to blame.

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Is there a vapor barrier (plastic sheeting) on the ground in the crawl space?  Is the fiberglass insulation faced with the backing toward the floor (up)?  Any wet spots under the house or drainage issues around the house?

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There is a partial vapor barrier now and a new one will be installed. The fiberglass faces up towards the floor. No water coming into to the crawlspace.

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15 hours ago, Patton said:

There is a partial vapor barrier now and a new one will be installed. The fiberglass faces up towards the floor. No water coming into to the crawlspace.

The floor insulation was installed backwards, the facing always goes toward the inside of the home. That's likely the biggest part of the problem. Completing the vapor barrier will help. You'll also need to check for mold and rot in the subfloor. 

If the closets stay closed all the time, lack of airflow contributes to moisture build-up.  If the closets are on an exterior wall, the temperature difference will also contribute. 

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The paper faces down towards the vapor barrier and the pink insulation faces up towards the roof. I don’t know if that is what you are describing or not.  The plan is to have the insulation ripped out, and the wood sprayed with Borate. There is not any wood decay and very little fungus. Then the vapor barrier will be replaced.  I am wanting to avoid replacing the insulation.

 Is there a requirement for there to be insulation in the crawlspace?

Edited by Patton

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Your insulation was installed backwards.  That is likely a large part of the problem.  

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My 34 year old home is also insulated like Mr. Pattons. Altho the prior owner had the crawl space vent holes sealed. Luckily, the crawl space is relatively dry and I'v check for black mold up under the fiberglass in spots and found nothing. As mentioned by No-One, the best thing to have in a case like these is pull the insulation out, Foam board the cinder block walls and then have the ground plastic sheet heat sealed so you have a zero moisture penetration from the ground up into that crawl space. The only reason I can think of, of putting Borate up on your floor joists is if you have a termite problem. Boring bugs stay away from it.

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I’m surprised an inspector didn’t catch it - either when the home was built - or when you bought it. 

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Yes, that's backwards. The paper (which is more than just paper, it's a vapor barrier) always faces toward the heated space, regardless of where it's installed.  

I'm no expert, but I don't think there's a requirement to insulate anywhere. Most heat is lost through the ceiling and walls, so those are most commonly insulated.

My house didn't have insulation in the floors or a vapor barrier in the crawl space when I bought it 13 years ago, it's 25 years old now.  I installed both, and more attic insulation, and immediately noticed a difference in how the house felt inside and my AC bill dropped noticeably. I paid someone to do the insulation as they charged me less to install it than I could buy the insulation for. 

Edited by peejman
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In the late 80s I worked for Terminix in the Memphis area for 9 months. I never saw insulation under any house. I laid out a lot of vapor barrier under houses. It was 6 mil plastic, 4 ft x 200 ft rolls, 4 rolls per case. Let it lap over 6" and use nails to staple it together. I did my sisters house and she said she could feel the difference during the winter.

My second wife wanted to spend our honey moon in Nashville. While there we visited a college friend. They were working on the crawl space. It was tall enough to stand in about a 3rd of the house. They had dug out to level the floor, trenched for water flow to the sump pumps. Laid down vapor barrier and covered it with crushed limestone. First time seeing insulation in the floor joist.,It was installed the right way. After wiring in lighting he wanted to staple insulation to the joist the wrong way and cover the joist. I talked him out of it. A couple of months later I passed a construction site where a large, tall metal building was on the way up. There was a large pile of 2" x 28" x 40" sheets of Styrofoam used in packing of the metal siding for shipping. I packed my truck with all I could carry. I read about it on the internet that night.  It will breath were paper will not. It was carried to Nashville our last trip there. They cut the foam so it fit between the joist tight and painted the bottoms of the joist. The picture I was sent looked great.

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House we bought last year had insulation installed upside down and moisture was a real problem in crawlspace and lower garage. We ripped all the insulation out and encapsulated the basement. Several people told me the floor would be colder underfoot if we didn't put insulation back. I chose not to. Floor is warmer than before, no moisture, and the house is much warmer. We've actually turned the thermostat down 2 degrees and still feel warmer. 

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I do handyman work on the side and end up in a lot of crawl spaces. The vast majority of homes that I go under, new and old, have no insulation in the crawl space, so I can’t imagine that it could be a code requirement to have it.

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Patton

"The moisture in the crawlspace really isn’t bad but some of our closets would get mildew"

Would it be prudent to get a moisture meter and get some actual test numbers?   Before and after the fix.   Documenting the results.   Test results before and after in the closets also.

Morgan88 

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