Insulating basement with partial crawlspace?

I inspected a home with a below grade unfinished basement with two partial crawlspaces that were open to the basement. There was gas HVAC equipment, plumbing, etc in this area but no heat source or return vent. I feel the area should be insulated but do the walls get it or the floor? Also, no vent opening for the crawlspace incase your wondering.

Can you post pictures and location?

There ya go !

The area with the ceiling tiles and wood wall panels is all part of the unfinished area as well

If the space is not conditioned, why insulate? It is not part of the conditioned building envelope. The overhead floor structure should be insulated.

Unventilated crawlspaces should be conditioned (dehumidifier).

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So are you saying if there was a HVAC vent, the walls would need to be insulated but since there is not only the floor joist need to have it?

If the crawlspace is open to the basement, it is in my opinion a conditioned space and the walls should be insulated.


You could insulate the basement walls and the floor structure over the crawl area.
Or you could insulate just the floor structure everywhere.
Or you could insulate the crawlspace walls.
One of the three above would complete your insulating of the building envelope.

Now, the crawlspace is not ventilated which is incorrect unless the crawlspace is conditioned. Separate issue.

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The OP stated the crawlspace was open to the basement. I don’t think you would want to vent it in this case. At least not in Minnesota!

I do not disagree. But, look at all that moisture wicking thru the CMU block. I would bet a $1 there is mold in multiple areas including the basement.

Even with louvered doors, that is what I think and have done in my own homes, Ryan. And it worked great!

We used to put he crawlspace vents in (due to the code requirement around here) and then seal them off when the AHJ gave us our Certificate of Occupancy. It made a fine basement and crawlspace together by insulating the walls of the crawlspace and sealing the floor (dirt).

Sometimes codes don’t make sense.


I agree on that point. My recommendation to the client in this case wouldn’t even be related to insulation, unless local code states that an energy wall must be installed. I would focus on the moisture.


And today, if you did that and added a dehumidifier you would you would be code complaint. :smile:

If the crawl space is connected to the living space with no door the exterior walls should be insulated whether it’s conditioned or not. If the crawl space were not connected to the living space the floor could be insulated.

Deal with that moisture on the exterior where it is coming from. IMHO :grin:

Even so, we used 2 sided foil faced rigid insulation and ran the dirt floor moisture barrier up the walls about 6" and sealed it to the insulation really good. :grinning_face_with_smiling_eyes:


I’ve never seen good results with insulating under the main floor in the crawl space. In my area it always ends up being a big moisture problem.


I agree, it is typically saturated and falling. However, new building standards require a vapor barrier have lapped and sealed sides as well overlapping seams.

In my area with high humidity, venting a crawlspace is useless in my opinion. I have seen very good success with non-vented crawls with dehumidification and a good vapor barrier.


I agree, Christopher, we insulated the crawlspace walls only definitely NOT between the floor joists above.


@pmccoy3 That is an interesting basement for sure. It looks like the crawl areas have louvred doors in the opening, is this correct? That IMO would make the crawl areas part of the conditioned space. And windows into the unfinished utility area? :thinking:

In the last picture, looks like efflorescence on the CMUs. Moisture issue. Insulation on damp walls = bad juju.

Where are you located??? That in of itself can be a determining factor.