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Discussion Starter · #1 ·
I had previously posted about our 1960s/70s crawlspace and am still in the process of trying to control water infiltration through/over the foundation walls due to high grade and very heavy uncontrolled rainwater.

I removed some 1/2” yellow foil faced insulation from the walls to help control the smell, so now the walls are bare. There are a few vents to outside through the siding in rim joist areas, and uninsulated HVAC ducts run through the space but don’t output any air there.

Which of the following should I do?
  1. Block the outside vents and all rim joist bays with XPS and spray foam (a little concerned about doing this before the water issue is 100% solved because I don’t want any of the moisture to just end up being trapped and rotting the wood, there were a few inches of standing water down there after the last heavy rain).
  2. Put XPS on the floor and walls, again a little concerned about effects of trapped moisture or standing water damaging
  3. Cut into one of the HVAC ducts running through the crawlspace and add a vent that points down into the crawlspace (or some other method) to utilize the HVAC system to condition/dehumidify that space to the same temperature as the rest of the living space (~750 sqft on this 1.5T/45k-80% HVAC system, crawlspace is about 200 sqft and 3ft high)
  4. Don’t do anything with the HVAC, just run a humidifier down there
  5. Do some of these things after controlling the moisture

    Here are some photos of the space:
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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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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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retired framer
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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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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.


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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Discussion Starter · #6 ·
Thanks for all the input as usual.


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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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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Discussion Starter · #8 ·
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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"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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Discussion Starter · #10 ·
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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retired framer
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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.
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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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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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