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Insulate crawlspace walls or insulate floor joists?


Oopey's Avatar
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01-24-15, 03:23 PM   #1  
Insulate crawlspace walls or insulate floor joists?

I want to spray foam the walls of my crawlspace to warm the above floor, not worry about humidity (running two humidifiers is expensive!) and not worry about frozen pipes (all pipes run through the unconditioned crawlspace and are not insulated).

The walls are blocks, and the ground is poured concrete (from the 1950s). I had two estimates from companies I trust, and both companies said that I don't need to worry about vapor barriers for the ground because its poured concrete. I know new foundations are built with vapor barriers, but I'm not sure if ours has one. Both companies said regardless of whether or not there is a vapor barrier built in, I still don't need to worry about putting in a vapor barrier. Both companies went down in the crawlspace and said moisture is coming thru the walls and not the ground (I guess no wet spots or something?) One of the two companies also used a thermal camera.

The third company I called said that I should instead spray foam the crawlspace ceiling and then also insulate all the pipes that are down there, i.e., not worry about the crawlspace walls. They said that I should definitely worry about moisture coming up through the ground and that if I condition the crawlspace I might have moisture issues. At their suggestion, I am running a test wherein I taped down a 2'x2' piece of 4mil plastic; I'll wait 2-3 days and then see if any moisture is trapped. (They have not yet come for an estimate, they wanted me to do this test first.)

So, my question: is the third company right? Do I need to worry about moisture coming up even if I have poured concrete floor? I'm very unsure of what to do if my test shows some moisture.

 
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01-24-15, 04:04 PM   #2  
Your test will show moisture as you don't live in the Nevada desert, there is moisture down there. But is it enough to worry about. Think about the gallons of water you are adding with those humidifiers. You did say "running two humidifiers is expensive!" and didn't mean dehumidifiers. So a little extra moisture may be good.

Check local codes to see if the spray foam will need to be covered with a fire rated barrier. Spray foam companies often neglect to mention this as it increases the cost of their total job. In some cases a local code official may not require such in a crawl space, but best to check.

Insulating the walls and then conditioning the space down there will handle any small amount of moisture from the floor. it will also give you nice warm floors . When you insulate the floors the only heat reaching then comes from above and we all know where that warm air heads, up. Warming floors from above is a frequent problem which conditioning the crawlspace will eliminate.

Bud

 
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01-24-15, 04:46 PM   #3  
Whoops, I meant "dehumidifiers." Sorry! (Does that change what you said?) I already got the actual estimates from the two companies, which did not include anything about fire barriers; I will ask them if I need a fire rated barrier (or I guess I should call the town construction office?)

Assuming I do spray foam the walls, I am then considering the crawlspace to be "conditioned." I was not planning on dropping a baseboard loop from the boiler into the crawlspace to heat it (we have no utilities in the crawlspace; they are all up on the first floor - only thing in the crawlspace is a sump pump). The insulation guy thought his company would charge about $1,000.00 to drop a loop, but recommended not doing it until I could test temperatures after conditioning to see if I actually needed a loop down there.

Also, the two companies apparently use different foams:
Company A - 2" High Density E-84 closed cell, R-15 value
Company B - 2" Lapolla Foam Lock closed cell, R-13 value

Company A is about 75% more expensive than Company B. Worth it for an increase in R-value by 2 and/or for the different type of foam?

Thanks again.

 
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01-24-15, 06:56 PM   #4  
No real experience with the different types of foam. R-2 is really no difference.

Yes, running two dehumidifiers makes a huge difference, since most homes in the winter run exceedingly dry. This says you have a very large source of moisture that needs to be identified before you spray those walls.

If moisture is coming through the walls, then you first need to be sure the drainage around the house is directing the runoff well away from the foundation.

You mentioned a sump pump, does it run often?

To be sure those dehumidifiers were actually removing the amount of water I'm concerned about, do you have any idea as to their output?

Another point, if you spray foam the tops of the walls where the house rests on the foundation, a common area to air seal when adding foam, it will reduce the air exchange and increase the humidity inside the home.

A 1950 home should not be very tight. Has any air sealing or other energy efficiency work been done? Adding new siding with a well taped layer of insulation under it will do a good job of air sealing and increase the inside humidity.

I'll let you sort that out before continuing.

Bud

 
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01-25-15, 11:34 AM   #5  
Thanks again for the info.

We run the dehumidifiers from approximately March or so until maybe about September. So we don't seem to need them in the winter months (I'm just going by what others have said to do in the past).

Exterior grading has been corrected a year or two ago; gutters/downspouts extend away from the house. We just happen to be in an area with a high water table (I've been told its because of a few very nearby lakes). None of the houses in my area have basements, just crawlspaces.

Sump pump does not run all that often. During a thunderstorm, it might run once every 2-3 hours or so. Otherwise, maybe once every few days? (I'm not usually home during the day, but I know that I generally don't hear it.) The dehumidifiers drain directly into the sump pump pit, so I don't think they are taking tons of water out of the air.

We have had an energy audit done, including lots of additional insulation added and replacing high hat lights with the new ones that restrict air flow (blower door test showed huge improvement after the work was done). The foundation and first floor are 1950s, but second floor was entirely added in 1999-2000. The siding is from 1999-2000, so I'd rather not replace it.

So, my goal is to reduce humidity, not worry about frozen pipes and increase overall efficiency. Warmer floors would be nice, but not a requirement. So - do you suggest spray foaming the walls (including the wood framing just on top of the walls)? Or spray foaming crawlspace ceiling and insulating pipes against freezing?

Thanks again for all the help.

 
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01-25-15, 01:12 PM   #6  
IMO, I would foam the walls and leave the crawl ceiling/floor above fully accessible.

Bud

 
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01-25-15, 06:44 PM   #7  
Ok, so no real need to worry about moisture coming through the concrete floor, even if no vapor barrier was installed when the floor was poured.

Thanks for the help and advice!

 
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