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Old 01-24-2011, 08:54 AM   #1
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Air leaks through floor from insulated crawl space


I recently bought a house that is about 100 years old. While I was insulating the crawl space, those above, in the house, could see my work lights shining through chinks in the floor. There is no sub-flooring under the finished pine planking! This winter lots of cool air from the crawl space is leaking into the house. Does anyone have any suggestions on how to resolve the air leaks? Can I put house wrap or felt paper between the floor joists? I am concerned with moisture accumulation, so I am not sure how to do this to fix the air leaks while not creating a moisture and mold problem as a result.

Thanks for any suggestions.

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Old 01-24-2011, 12:27 PM   #2
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Air leaks through floor from insulated crawl space


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Originally Posted by fdpelli View Post
I recently bought a house that is about 100 years old. While I was insulating the crawl space, those above, in the house, could see my work lights shining through chinks in the floor. There is no sub-flooring under the finished pine planking! This winter lots of cool air from the crawl space is leaking into the house. Does anyone have any suggestions on how to resolve the air leaks? Can I put house wrap or felt paper between the floor joists? I am concerned with moisture accumulation, so I am not sure how to do this to fix the air leaks while not creating a moisture and mold problem as a result.

Thanks for any suggestions.
Cut foamboard insulation and fill in the joist bays. Use foam in a can to fill in any gaps. There's an issue of it being a combustible material so you might want to use a dense fiberglass batt to avoid covering the foam with a non combustible material.
Ron

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Old 01-24-2011, 12:46 PM   #3
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Air leaks through floor from insulated crawl space


Thanks, Ron. Is there any issue with moisture being trapped in the crawlspace if I use foam board, since I have batt insulation on the crawlspace walls and no venting?
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Old 01-24-2011, 01:32 PM   #4
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Air leaks through floor from insulated crawl space


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Thanks, Ron. Is there any issue with moisture being trapped in the crawlspace if I use foam board, since I have batt insulation on the crawlspace walls and no venting?
I don't understand the batt insulation on the crawl space walls. Is this batt insulation against the concrete?
What about the floor? Concrete? Dirt? Is there a vapor barrier? What is the humidity level in there now? Other times of the year? If you don't know, pick up some humidistats and set them up.
You're speaking of the crawl space as individual features. It's a system and needs to be addressed as such.
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Old 01-24-2011, 02:31 PM   #5
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Air leaks through floor from insulated crawl space


It is a dirt floor with vapor barrier. And yes, the batts are against the walls, which are brick. Humidity is low, but I don't know exactly what the level is. I understand the system concept, from the standpoint of the crawlspace being a conditioned space.
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Old 01-24-2011, 02:45 PM   #6
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Air leaks through floor from insulated crawl space


Like Ron said, cut foamboard to fit between joists, that should help.

But you really want to think about putting down a subfloor over the pine planks, and then laying a new wood floor over that.

I'm just guessing, but I bet the floors in your house bounce really bad? And the "finished pine plank" floor you speak of, are the planks about 6" wide?
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Old 01-24-2011, 03:59 PM   #7
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Air leaks through floor from insulated crawl space


Mabc, thanks for the reply. Actually, they are about 3" wide, but the widths vary somewhat. They are nailed down with cut nails. I don't know what construction was like 100 years ago, so I don't know if this was originally subflooring or not. From what I know, there was linoleum over the top previously. The floor is definitely bouncy!
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Old 01-24-2011, 04:01 PM   #8
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Air leaks through floor from insulated crawl space


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Originally Posted by fdpelli View Post
It is a dirt floor with vapor barrier. And yes, the batts are against the walls, which are brick. Humidity is low, but I don't know exactly what the level is. I understand the system concept, from the standpoint of the crawlspace being a conditioned space.
It's good that you're aware of the system, but when you post, I think it's a good idea if you give us an overview of the whole situation.
The batts against the bricks will probably trap moisture in the Summer if it's like many places in the US. I'd check it next Summer if you get
50%+ humidity in the space.
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Old 01-24-2011, 04:30 PM   #9
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Air leaks through floor from insulated crawl space


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Originally Posted by fdpelli View Post
Mabc, thanks for the reply. Actually, they are about 3" wide, but the widths vary somewhat. They are nailed down with cut nails. I don't know what construction was like 100 years ago, so I don't know if this was originally subflooring or not. From what I know, there was linoleum over the top previously. The floor is definitely bouncy!

Yeah man, that's the original subfloor, you really need to think about putting down some tongue and groove plywood over it (the thicker the plywood the better) make sure to glue and screw it down.
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Old 02-07-2011, 11:27 AM   #10
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Air leaks through floor from insulated crawl space


I would strongly suggest that you consider , a technique that completely isolates the crawl space from the outside air and from the ground, including it in the internal building envelope. For a number of reasons:

1 - It is probably the most affordable option for you at this point.
2 - It will completely solve two problems at once and for good: the energy waste (cold drafts through the floor) and moisture problems, protecting your crawl space from mold, dry rot and structural decay.
3 - It is proven to make the whole house an average of 18% more energy efficient.
4 - Depending on where you live you might not need crawl space insulation at all.

Another word of advice: if you are using fiberglass batches against the walls or anywhere in the crawl space you are most likely wasting your money. Fiberglass soaks moisture like a sponge, and as it does, it loses all it's R Value. Not to mention that, in the mold remediation industry, they call it "mold candy".

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Last edited by Gary in WA; 02-07-2011 at 02:06 PM. Reason: Ad link in post body
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