Insulating crawl space?

[David Paul]

My daughter bought a new construction home here in NJ. Built on an uninsulated crawl space. Last winter the floor was quite cold. I’ve heard you can spray insulation or use batt insulation in the floor joists. Not sure which is the best way to insulate this space. Crawl space has some ventilation and a cement floor. Any ideas are greatly appreciated.

 

[mike93lx]

There is no insulation in the floor? Wow.

IMO, best approach is fully encapsulate the crawl (easy since it is concrete), seal all the openings and insulate the walls of the crawl space. You don't want it to "breathe", you want it conditioned. What is the house using for hvac? Is there duct work in the crawl?

 

[cannuck]

If you just enclose the crawlspace with an insulated skirt, you will still have a cold floor as the pad beneath will be at ground temp (usually freezing in winter) . I would spray the floor with polyurethane closed cell, at LEAST 4 inches (about R30). 6" fiberglass might make you feel good, but won't do much to keep the floor warm and you would also need a vapour barrier. Much better to seal it up with foam.

BTW: "best practice" for an exposed floor is recommended at R50 just a few hundred miles North of you.

One way or another, I suggest you get in touch with a proven insulation contractor and take their advice.

 

[billconner]

Crawlspace should be interior - conditioned just like the house. Seal vents, cover walls and ground - look at Stego Crawl product - and insulate walls and rim joist area with foam. Don't insulate the floor - mildew, mold, and rot are certain

 

[fitter30]

Had a fiber insulated floor the mice had a very good time in it. Pulled out all the duct work sealed the air vents, insulation and have a crawlspace dehumidifier. Would like it spray foamed. Space never gets lower than 54°

 

[yeldogt]

My daughter bought a new construction home here in NJ. Built on an uninsulated crawl space. Last winter the floor was quite cold. I’ve heard you can spray insulation or use batt insulation in the floor joists. Not sure which is the best way to insulate this space. Crawl space has some ventilation and a cement floor. Any ideas are greatly appreciated.

Ductwork in the crawl ?

 

[David Paul]

No duct work in crawl space. The preventative bug service does not recommend spray foam insulation as it hides bug activity.

 

[billconner]

You can find a lot of stuff on internet saying he's to that claim, but leave the required 3" inspection strip and you'll be fine.

Very few dispute that uninsulated crawls are bad.

 

[WisJim]

A new house should have had an insulated crawl space to comply with most current building codes.

 

[turbowoodworker]

I too am surprised that a new house would not have a sealed and conditioned crawl space. That sounds just strange in 2022.

 

[David Paul]

Yea, I tend to agree with the last 2 posts. I’m pretty much going on what my daughter told me. Guess I’ll have to check myself next time I’m there.

 

[mike93lx]

I wonder why they did a concrete floor. That feels odd

 

[billconner]

As far as I can tell, the IRC does still allow vented unconditioned crawl spaces.

 

[Mzungu]

There is no insulation in the floor? Wow.

IMO, best approach is fully encapsulate the crawl (easy since it is concrete), seal all the openings and insulate the walls of the crawl space. You don't want it to "breathe", you want it conditioned. What is the house using for hvac? Is there duct work in the crawl?

Exactly this, for the least amount of problems let it become part of the conditioned space.

 

[Firebrick43]

If you just enclose the crawlspace with an insulated skirt, you will still have a cold floor as the pad beneath will be at ground temp (usually freezing in winter) . I would spray the floor with polyurethane closed cell, at LEAST 4 inches (about R30). 6" fiberglass might make you feel good, but won't do much to keep the floor warm and you would also need a vapour barrier. Much better to seal it up with foam.

BTW: "best practice" for an exposed floor is recommended at R50 just a few hundred miles North of you.

One way or another, I suggest you get in touch with a proven insulation contractor and take their advice.

The ground temp under the house doesn’t change much from summer/winter, and insulating the walls and conditioning the space makes a world of difference in my experience. I made a trim metal termite edge to jamb into The sill and caulked. Then I chipped away some of the excess concrete from the form ties and shoved 2’x8’x2” eps foam onto the ties and used a foam gun to seal around the seams. If you don’t have ties just glue the foam onto the wall after brushing it clean.

Most crawl space houses have the utilities under the house. I couldn’t imagine the night mare of working on pipes and such encased in foam.

 

[billconner]

There is not much heat loss into the ground below frost depth, where this slab must be. I would not try to insulate on top of the mud slab.

 

[Dig Doug]

Call 2or 3 insulation professionals have them out for a quote and inspection of the space, ask a lot of questions !

Don’t use the cheapest guy if he is way way lower than the other 2 guys!

 

[cannuck]

The ground temp under the house doesn’t change much from summer/winter, and insulating the walls and conditioning the space makes a world of difference in my experience. I made a trim metal termite edge to jamb into The sill and caulked. Then I chipped away some of the excess concrete from the form ties and shoved 2’x8’x2” eps foam onto the ties and used a foam gun to seal around the seams. If you don’t have ties just glue the foam onto the wall after brushing it clean.

Most crawl space houses have the utilities under the house. I couldn’t imagine the night mare of working on pipes and such encased in foam.

We seldom encounter crawlspace construction around here and the frost line is closer to 6' so not at all familiar with life in the Bannana Belt! Thus, why I/we tend to think in terms of heat loss to ground in winter terms. Where we DO see crawlspaces is under trailers, and those are thermal disasters in winter. I can see why (and how) you have treated your space to keep the utilities within the insulated envelope (which the OP does not yet have). I would still like to see some number of ground heat losses in what you describe as probably typical in your climate zone.

The thought process is more than morbid curiosity to to me as we have purchased a farm that sits on abut 10' of glacial till overlaying a hundred feet or more of clay. While it is normally pretty dry, a really wet year has the ground water table rise right to surface, so the only way to have a basement is to go slab-on-grade, build walls and backfill to make a yard. A lot of planning to decide what and where to insulate vs. include within envelope.

 

[u2slow]

My crawlspace is a slab also. Ive taken to insulating the perimeter walls.

The original floor insulation was inadequate in the first place, plus it had become rodent habitat. I was fighting it everytime I have to go in there to work on electrical, plumbing or HVAC.

 

[FrancisJ]

Just bought a renovation home (hobby of mine) where some sprayed foam chit (if you can believe it) between the floor joists in the crawl space -- talk about a nightmare - that crawlspace gets more water (trapped) than storm surge from many hurricanes.

Earlier reno had the floor joist insulation in "upside down" on hangars (LOL) --- another nightmare.

Encapsulate the crawl space perimeter and floor , leave the joists alone.

 

[David Paul]

I appreciate all the information you guys have provided here. The forced air HVAC is all in the attic. Hot water heater on the 1st and only floor. I will have her contact a couple of insulation contractors for estimates. I like the idea of insulating the crawl space walls approach.

 

[Sumboodie]

$40 buys a nice pair of slippers....

 

[David Paul]

$40 buys a nice pair of slippers....

Christmas is coming…..

 

[FrancisJ]

Mr Bill Conner zero'd in on it above --- the crawl space should be part of the "interior-conditioned" space. That design factor is what builders follow today.

 

[cannuck]

Just a few more thoughts on crawlspaces: I once built in the sub-arctic with a home standing on 40 piles down well below permafrost. I then build an insulated wooden basement to move the bottom of the insulated envelope 9' below grade. There was a footing on the piles and a wooden floor in the basement - of course with a "crawl space" below. Over time, some permafrost melted and became ground water in the sub-basement and had to be set up with a permanent collection point and pumpout. Even so: warm, most air is a perfect breeding ground for all kinds of organisms. That is why I worry about moving the lower thermal barrier down to open ground. Of course with a pad much simpler, but I am sure that even in the most moderate NA climate you would be surprised how much heat can be lost to ground (that could be a very GOOD thing if air conditioning is your largest cost).

 

[larry4406]

The kitchen extension at our house I did an 8x16’ conditioned crawl space.

It’s got normal perimeter 4” perf drainage system with footer weep holes and it’s own sump crock and pump. Block walls core filled. Outside of walls parged and GMX waterproofed. Inside there is a 4” concrete slab over 6 mil vapor barrier. Applied UGL Drylock extreme to inside of block walls as a precaution. Walls and band board were close cell spray foam insulated to R21. There is a 6” duct connected to the space with a 4x10 register.

I think there is around 30-32” height in there.

Built just like a basement.

 

[billconner]

The kitchen extension at our house I did an 8x16’ conditioned crawl space.

It’s got normal perimeter 4” perf drainage system with footer weep holes and it’s own sump crock and pump. Block walls core filled. Outside of walls parged and GMX waterproofed. Inside there is a 4” concrete slab over 6 mil vapor barrier. Applied UGL Drylock extreme to inside of block walls as a precaution. Walls and band board were close cell spray foam insulated to R21. There is a 6” duct connected to the space with a 4x10 register.

I think there is around 30-32” height in there.

Built just like a basement.

smart!

 

[mike93lx]

Looks good, my only concern is that if you ever have a leak from exterior flashing, where the rim joist or "BAND" is exposed to moisture, it will rot and you will never see it. Additionally, you should always leave a 2-4 inch gap for a termite inspection window. It's code down here in NC, not sure where you are.

Hunting for old posts to revive isn't a great way to start