# Crawlspace insulation and conditioning



## stick\shift (Mar 23, 2015)

Obviously, you know the water problem has to get resolved. After that, looks like a concrete floor so no additional vapor barrier would be required on the floor. After that, it's your call - you either seal a crawlspace from the outside and open it to the conditioned house air or you seal it from the house and open it to the outside air. In the former, you insulate the walls and in the latter you insulate the ceiling. The further south you go, the more you find the space vented to the outside but there are no hard and fast rules.


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## jim_bee (Feb 23, 2021)

I think your first priority is to control the water--if you can't prevent intrusion from the outside by regrading & installing a foundation drain, then you need to channel it to a sump pump. Then, as stick/shift says you can either insulate the walls with foam and close the vents or insulate the between the floor joists and keep the vents. I don't think you'd get much benefit from insulating the concrete floor. In other words, do #5.


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## Nealtw (Jun 22, 2017)

Solve the water problem. Insulate the ducts and floor and leave the vents as they are. 
Conditioning that space is like heating the basement where the air will always be cooling so It will have higher humidity and condensation from the same upstairs air.
So you will need a dehumidifier running 24/ 365.


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## Dave Sal (Dec 20, 2012)

Your crawlspace sort of looks like mine. I have a tri level house and the crawlspace is under the main floor at ground level. I live in the Chicago area and during winter, the floors on the main floor would always get really cold and uncomfortable to walk on unless you had shoes on. I put a remote thermometer down there and the temps would get down to just above freezing. Some of the heat ducts run down there and they are uninsulated, same as the copper water lines going to the kitchen. I was afraid that the water lines would freeze. Anyway, I read about crawlspaces on Building Science.com and decided to follow their recommendation. 






Info-512: Crawlspace Insulation


Read this in depth information sheet discussing crawlspace insulation, addressing issues from condensation and drainage to how to approach vapor permeance.




www.buildingscience.com





I closed off the two vents to the outside, one on each side, and insulated the rim joists with rigid foam board, sealing the edges with Great Stuff. The vents were also covered over with the foam board. After the job was complete, I found that the temperatures down there stay around 63 degrees all year round. The floors above are no longer ice cold during the winter and I no longer worry about the copper pipes freezing.


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## wrbrb (Aug 18, 2020)

Thanks for all the input as usual.




Dave Sal said:


> I closed off the two vents to the outside, one on each side, and insulated the rim joists with rigid foam board, sealing the edges with Great Stuff. The vents were also covered over with the foam board. After the job was complete, I found that the temperatures down there stay around 63 degrees all year round. The floors above are no longer ice cold during the winter and I no longer worry about the copper pipes freezing.


Interesting - I’m also in the Chicago area. This sounds like a different approach than the other suggestions. You blocked the vents and insulated the rim joists, but didn’t insulate the walls or ceiling or vents/pipes, nor are you actively heating or cooling the space with your HVAC?

I wonder if the lack of that active heating/cooling in the crawlspace prevents the condensation issues Neal mentioned, while the rim joist insulation and vent blocking gives you a constant temperature that doesn’t affect the heating or cooling of the house much, even in extreme outdoor temperatures?


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## SPS-1 (Oct 21, 2008)

I would think the floor joists is where you want a vapor barrier and insulation. 
After that, the crawlspace is unconditioned and would be vented. Sprayfoam is a possibility for achieving both. Existing vents don't look like much venting. 
Sump pump is the simplest way of getting rid of the water. But as @jim_bee pointed out, might need some method of getting the water to the pump -- not sure of best way to do that.


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## wrbrb (Aug 18, 2020)

Thanks. I do plan on resolving the water issues, hopefully with downspout rerouting and French drains, but I’m hesitant to insulate the rim joists or walls for fear of water coming back and getting trapped and damaging the wood.

Maybe that means leaving the space unconditioned and vented is the best approach, and insulating the ceiling and ducts. Then if water did get in again, it wouldn’t damage any insulation and could breathe to dry out.

Is there a typical way to enlarge vents like the ones I have (aluminum siding) if necessary?


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## Dave Sal (Dec 20, 2012)

"You blocked the vents and insulated the rim joists, but didn’t insulate the walls or ceiling or vents/pipes, nor are you actively heating or cooling the space with your HVAC? "

Correct. Floors are concrete but thankfully I never had any issue with water intrusion. The heating duct seams are sealed with foil tape but other than that, nothing was done as far as insulation for the HVAC ducts. Insulating the rim joist and closing the outside vents made a huge difference. Before I did that, during the summer it would get musty down there as the outside humidity would enter the space.

The crawlspace is sealed from the rest of the house except for the area over the below grade bathroom and a small opening in the utility room between the exterior wall and the shower stall for the bathroom. There is also an opening of about one foot between the upper floor joists and the top of the bathroom ceiling that are open to the crawlspace.


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## wrbrb (Aug 18, 2020)

If I want to insulate the ceiling, what kind of insulation is recommended? 

For between the joists, would I use batts face down (maybe R-19?), stapled to the joists - or rigid foam in each cavity with spray/can foam?

For the ducts, would I just wrap them where possible with something like R-6 wrap and foil tape, and if I can't reach up and around to the tops of them just try to fit the R-19 batts around them as best I can?


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## Nealtw (Jun 22, 2017)

wrbrb said:


> If I want to insulate the ceiling, what kind of insulation is recommended?
> 
> For between the joists, would I use batts face down (maybe R-19?), stapled to the joists - or rigid foam in each cavity with spray/can foam?
> 
> For the ducts, would I just wrap them where possible with something like R-6 wrap and foil tape, and if I can't reach up and around to the tops of them just try to fit the R-19 batts around them as best I can?


Anything inside the insulation is inside the envelope, When you insulate the floor you go around the ducts so that are inside the envelope. That part of the floor and the top of the duct do not need insulation. You might insulate the top of the duct for performance but not for the envelope. 
In basement we frame in duct work and some people insulate that for noise. I think ducts in a crawl space or attic should just be included in the envelope the same way.








Consider the subfloor as the warm side and it is the vapour bearier. So no paper needed, FB bats or rockwool both work but the fit is important and usually need chicken wire or something to hold them up.


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## jim_bee (Feb 23, 2021)

You could use fiberglass or rock wool batts for the ceiling or have it spray foamed. If you use batts or rolls with a backing, the backing should be to the conditioned side (up in this case). Support the batts with insulation supports. 

Insulate the rim joist by cutting foam insulation to fit and then spray foam the gaps.


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## wrbrb (Aug 18, 2020)

After reading a lot, I’m now wondering if it might be best to actually treat this entire crawlspace as conditioned space.

I would block the vents with 2” XPS foam, and use that in the other rim joist bays as well, sealed with expanding foam.

Then with the HVAC ducts that run through the crawlspace (serving the room above) radiating heat in the winter in heating mode and cold in the summer in AC mode, that might be enough to keep humidity at bay down there?

Access to the crawlspace is through the floor above (in a closet with bifold doors where the furnace is located - not from outside). Maybe it would make sense to turn that access hatch in the floor into a vented hatch to help equalize temperature and humidity between the first floor and the crawlspace?


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## bbender716 (Nov 29, 2021)

Another fellow Chicagoan here! I actually encountered a very similar situation.

I addressed the water issues from the outside as best I could by improving grading and downspouts/gutters etc.

Then I installed an Aprilaire crawlspace dehumidifier and ducted it with insulated flex duct 

Then I insulated the rim joists with 2"XPS foam and also spray foamed the space between the sill plate and foundation.

Last remaining things I have to do is tear out the batt insulation the previous owner put in some of the rim joists and replace with rigid foam, then put up XPS board on the crawl walls. Hopefully then the dehumidifier runs much less frequently.


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## wrbrb (Aug 18, 2020)

bbender716 said:


> Another fellow Chicagoan here! I actually encountered a very similar situation.
> 
> I addressed the water issues from the outside as best I could by improving grading and downspouts/gutters etc.
> 
> ...


Interesting to hear your progress and plan. I’m hesitant to install a dehumidifier - I would rather not have the electricity expense and have a piece of equipment down there if I can avoid it. If my drainage/grade system works and I block the vents, I don’t know where any humidity would come from. Keep us updated on your progress because I’m interested in what each step does to improve the situation.


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