# Crawl space insulation question



## gregsenne (Feb 16, 2009)

Hi,
My crawlspace (24x15) is cinder block walls, and about 3 ft tall with a gravel floor and vapor barrier under the gravel. There are two vents on opposing sides at the top of the cinder block. There is also R9 blanket insulation laid up against the cinder block, and that fiber tar substance sprayed on the outside of the wall. The entire crawl space besides the top block is underground. Rim joists are insulated with R49 and sill plate has the blue stuff between the cinder block and sill plate.
Builder told me that the blanket insulation was only so the wall would not sweat. 
The crawl space also has uninsulated water lines and ductwork in it. Never had a problem with frozen pipes. Also, the crawl space is COMPLETELY sealed from the basement with plastic sheeting vapor barrier which is caulked to the ceiling, walls, and floor, and the basement walls are insulated.

My tile floor above the crawl space is VERY cold. Much colder than my other rooms with tile that are above the conditioned basement. 

I have enough fiberglass R19 laying around to insulate the crawl space ceiling, but only enough to do the ceiling over the tiled bathroom, and not my carpeted bedroom (which is also over the crawl space). 

So here are my questions:
Will insulating the ceiling just under the tile bathroom help?
Would it be better to insulate the crawl space better? It seems like majority of my cold comes from the two vents (even though they are closed in winter, they still let alot of cold air in). 
Do I need those vents in my crawl space? Or can I completely seal them up with some foam board and expanding foam?


Thanks for the help!


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## Windows on Wash (Aug 30, 2011)

gregsenne said:


> Hi,
> My crawlspace (24x15) is cinder block walls, and about 3 ft tall with a gravel floor and vapor barrier under the gravel. There are two vents on opposing sides at the top of the cinder block. There is also R9 blanket insulation laid up against the cinder block, and that fiber tar substance sprayed on the outside of the wall. The entire crawl space besides the top block is underground. Rim joists are insulated with R49 and sill plate has the blue stuff between the cinder block and sill plate.
> Builder told me that the blanket insulation was only so the wall would not sweat.
> The crawl space also has uninsulated water lines and ductwork in it. Never had a problem with frozen pipes. Also, the crawl space is COMPLETELY sealed from the basement with plastic sheeting vapor barrier which is caulked to the ceiling, walls, and floor, and the basement walls are insulated.
> ...


There are bunch of threads on crawl spaces with people going through nearly identical situations. This board is a wealth of information.

Conditioning the crawl is the best bet.


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## gregsenne (Feb 16, 2009)

Thanks for the reply. That's kinda what I was thinking of doing. 
My walls are already insulated and so are my rim joists. So, really all I need to do is block those vents off and add some ductwork.

Thanks!


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## gregsenne (Feb 16, 2009)

Ok one more question. When I google image search "conditioned crawl space", I see pictures of crawl spaces with white barrier material all over the floor and up the walls and up the cinder block supports in the middle of the crawl space.
Do I need this? 

When we built the house, after the footers were poured and the block walls were laid, we laid a vapor barrier on top of the dirt and then filled a few feet of pea gravel on top of the barrier. The barrier is not sealed to the walls (I dont think) and there is no barrier that goes up the cinder block walls or cinder block supports. The insulation, however, has a barrier on the back side of it that is stapled to the sill plate and touches the gravel (but not attached any way at the bottom). The insulation is between this barrier and the cinder block wall.

The house was built in 2009 and there is currently absolutely no signs of moisture in my crawl.

Thanks again.


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## Windows on Wash (Aug 30, 2011)

You will need to insulated those areas differently to do it properly.

Fiberglass is not well suited for crawlspace stem walls (moisture, mold, etc) and the fiberglass in the rim joists is doing nothing to stop the air leakage.


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## gregsenne (Feb 16, 2009)

So, foam board and spray foam is my best bet?

If (for now) I were to leave the fiberglass against the walls and rim joists, and just sealed the vents and added a duct, would I be better off than I am now?

Basically, I'm looking to make the tile above the crawl space warmer, but not at the expense of a higher utility bill. 

Thanks.


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## HomeSealed (Jan 3, 2008)

You won;t have a higher utility bill. As WOW said, seal up the vents and insulate the space properly... Yes foam board and Spray foam are best. Also, be sure to use the correct foam board as Rob O. mentioned. Thermax is good, just very pricey. There is a generic version of it as well, but the name escapes me.


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## Gary in WA (Mar 11, 2009)

http://www.advancedenergy.org/buildings/knowledge_library/crawl_spaces/pdfs/Closed Crawl Spaces.pdf



Whoops, old thread...

Gary


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## operagost (Jan 8, 2010)

Eh, not that old! That report is definitely interesting, though. Other sources, like Building Science, suggest that insulating the foundation walls in a closed crawlspace is sufficient. This report suggests that the floors should still be insulated. I've been considering doing that in my closed crawl (in SE PA), because the floor temp still drops as low as 60F when it's in the 20-30F range outside. While I probably could do more to air-seal the rim joist, I'm sure that I will still need to provide more heat in the crawlspace and expected that might actually INCREASE my heating costs. Their research seems to have come to the same conclusion in Flagstaff. SE Pennsylvania is slightly warmer and a lot more humid, putting it somewhere in between Flagstaff and Baton Rouge, so interpretation of this report is tricky. I wish they'd tested in a third, more humid/temperate environment like NJ, PA, VA, or OH.


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## gregsenne (Feb 16, 2009)

I ended up sealing up my crawl space vents with foam board and expanding foam. That alone has helped out. I also added a little bit of heat to the crawl space from one of the ducts that runs through it, and haven't noticed my furnace running more than normal.

I'm also going to put R19 batts in the floor joists. In that last link provided, it mentioned that efficiency decreased without the floor insulated because of the heat loss down into the crawl. This alone was a good enough reason to spend the money on floor insulation. The other reason I wanted to insulate the floor was because I had a bad shower leak above the crawl space, and I'm trying to hide the damage somewhat. (And no I'm not covering up a problem, I've already fixed the problem, painted all the joists with Killz, and replaced any damaged wood, however it's still noticeable that something happened there). Since the problem is fixed, I'd rather it not be blatantly obvious to whoever looks at buying the house next that there was a water leak.

For now I will leave the batts against the exterior walls, with the intention of replacing them with foam board later on.

Thanks everyone for the input.


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## operagost (Jan 8, 2010)

I read their North Carolina report from 2005 (a much more similar environment) and found that the results still suggested insulating the floor is better, although I can't see any reason that doing both (as my walls are already done with about 2" of foil-faced polyiso board) would be a problem. I only have issue with their use of kraft-faced insulation. One thing I'm sure of is that if that is used in conjunction with moisture-impermeable flooring (vinyl), you'll get high moisture in the subfloor and that will cause mold and/or your flooring will peel up. The people who did my place (before I owned it) hedged their bets, insulating the crawlspace walls AND ONLY the floor under the kitchen with kraft-faced fiberglass. Guess where the vinyl tiles are peeling up? I think I'll be pulling off the paper, and insulating the rest of the floor with unfaced boards or batts. I have a hydronic multi-zoned system, so trying to condition this area is not likely to be effective in my case.


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## Gary in WA (Mar 11, 2009)

http://www.buildingscience.com/documents/insights/bsi-009-new-light-in-crawlspaces/



http://termites101.org/termite-basics/termites-by-region


http://energy.cr.usgs.gov/radon/rnus.html

Gary


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