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Seal (but don't insulate) crawl space?


powpow's Avatar
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04-25-15, 10:13 AM   #1  
Seal (but don't insulate) crawl space?

I've got a crawl space that I'd like to seal, and wondering if it's crazy to just do that -- and skip insulating.

The crawl space is reasonably warm and dry, but a radon system is going in soon. I think that will draw more air through there, and I'd like to prevent pipes in the crawlspace from freezing.

Can I just use caulk or Great Stuff on the sill plate and rim joist, and skip the insulation step that most websites seem to show? I want to minimize the time I spend down there...

Hardcore professional spray foam is probably not an option for me. I'm wondering if a quick seal-up job will make a nice dent in things.

If I use Great Stuff, will that make my life harder if someday I do decide to insulate (I doubt that will happen, but who knows)?

Thank you for any input.

 
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04-25-15, 11:02 AM   #2  
If you can give us an idea as to your climate and perhaps add that to your profile it will be easier to answer. Insulation questions are directly related to a location and particular climate.

Bud

 
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04-25-15, 11:34 AM   #3  
Good point. I'm in Southwest Colorado. It is generally pretty dry, and it can get very cold in the winter here (lows in the teens or lower are not uncommon). Pipes certainly freeze. Summer temps are highs in the 90s. I think the elevation is around 5000 ft.

 
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04-25-15, 12:24 PM   #4  
We just insulated with R-19 fiberglas bats below the floor of a 12' X 24' crawl space with joists 16" on center and used those 16" long spring loaded support wires made by Simpson (packs of 100). That went pretty quick in comparison to the chicken wire I've stapled up in the past on areas like this.

How big is the area you're considering ?

Is a moisture barrier on the ground part of the radon mitigation ?

 
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04-25-15, 12:33 PM   #5  
Vermont,

I'm told the radon system will have "a cross laminated polyethylene" for submembrane depressurization. My limited understanding is that this will help pull any moisture out if it comes up (within reason of course, I doubt it'll dry out a puddle).

EDITED TO ADD: in other words, I think they lay down a plastic vapor barrier over the whole crawlspace. That is then attached/sealed to the foundation walls (and basement wall, where there is basement next to the crawlspace). So I think the answer is yes but I'm not sure.

The crawlspace is about 20x40 and another area about 10x13.


Last edited by powpow; 04-25-15 at 12:49 PM.
 
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04-25-15, 12:38 PM   #6  
I'm in favor of sealing a crawlspace and insulating the walls. Since you say it stays somewhat warm down there already, air sealing the perimeter will improve on that.

As Vermont asked, I assume the radon mitigation will include a full vapor barrier across the floor and sealed up the walls a ways. The exhaust fan for radon venting does not pull a lot of air from that space. They are intended to be sealed away from the crawlspace or basement as much as possible and create a negative pressure below the vapor barrier to ensure that any soil gas coming up through does not enter the crawlspace.

I would recommend you add at least a 1" layer of rigid foam insulation over those walls. If you use (and code official approves) a foil faced foam board it will provide the required ignition barrier. But just 1" would make a huge difference. Again, check codes they might require more.

Bud

 
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04-25-15, 01:58 PM   #7  
Also, in case a photo helps, I expect the floor of the crawlspace to look like the stuff on this page (but much less neat and tidy- the house is 70 years old). Again, my assumption is that also helps with water vapor, but I don't know.

 
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04-25-15, 02:07 PM   #8  
Something like 50% of the air you breathe flows through your crawlspace and up into the house, so keeping it well sealed is a major IAQ (indoor air quality) issue. I heat my basement and I enjoy the warmer floors. When you start air sealing where your house rests on the foundation you may find some surprises, most do.

Bud

 
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04-25-15, 02:26 PM   #9  
Heh... I'm assuming by "surprises" you don't mean warmer toes in the winter. More like black widows, gaps, shims, cracks, and generally more work to do....

 
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04-25-15, 04:18 PM   #10  
Building codes that I am familiar with require that crawlspaces be ventilated, if not to the great outdoors then to the living areas of the house. Not insulating the side walls will mean that you WILL lose heat through those walls.

 
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04-25-15, 04:20 PM   #11  
Yes "More like black widows, gaps, shims, cracks, and generally more work to do.... " but maybe "warmer toes in the winter".

I have found 1/2" gaps over 10 feet long. In my own house I discovered they did not fill above those tip down windows set in the concrete. A 1" high highway for the many mice I had been trapping for years. After I filled it with silicone they chewed right through and moved back in. Had to add some sheet metal to end that game.

Bud

 
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04-25-15, 07:10 PM   #12  
Well, you weren't kidding about surprises. I found out there's an additional/separate crawlspace under my house. I just recently bought the place... The inspector never noticed it. That one has even more spider webs and less room to move around.

Furd I don't know if it's to code or not but there is plenty of potential for venting to the living space (probably not intentional). Don't know what the requirements were when it was built.

 
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