Crawl space neither vented nor conditioned

Crawl space has its old vents blocked (cemented in pace) or no vents. Insulation of the floor above is missing. No ground vapor barrier present.

What do you recommend, to vent or to condition? this will determine what to do with the vents and insulation.

In my area (MN), I prefer conditioned. Seal the ground and install insulation on the perimeter walls. Basically treat it like a shallow basement.


I agree with Ryan.

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Kind of a long read, but really good information.

New Light in Crawlspaces | Building Science Corporation

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Kevin, thanks, I’m aware of the differences and the new preferred way. Just trying to see what others are recommending :slight_smile: In my area I can count on my hands the times I’ve seen an old house with a conditioned crawl space. They’re all vented, partially vented, or non vented – but not properly conditioned per today’s practice.

Got it Simon.

This is the note I put in all crawls that I find that aren’t sealed and conditioned.

The building science concerning crawlspaces has changed over
the years. The crawlspace should be considered as part of the
house, so what is in the crawlspace is also in the occupied areas of
the house. Best practices today recommend crawlspaces to be
encapsulated, the exterior walls insulated, and the air to be

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So which is it? That would determine my response

Neil, they vary between no vents to open vents. Why would it matter if the crawl space had no vents or cemented vents? In either case, unless the crawl was conditioned, it would be wrong and require some sort of recommendation.

So what would you recommend if the vents were blocked/cemented in place? and if the crawl had missing vents?

Encapsulating and conditioning a crawl is my pick. It controls moisture and mold under controlled conditions. But cost becomes a factor.

It is my choice, too, Brian.

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First i was thinking you were referring to a specific crawl inspection and not a generalized question, thus the question i asked.

If the vents were originally installed but have been sealed off, then i would recommend opening vents and installing v-barrier and add insulation under floor.

Adding conditioned air to a crawlspace may not be the most cost-effective means for my client dependent upon configuration of the crawlspace.

I agree having the crawlspace encapsulated with conditioned air is the best method but not always an option.

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Lots of regional differences for sure. In the Pac NW where I’ve done most of my inspecting, vented is best. Encapsulated can be okay but I’ve seen some mold problems when the fans fail. Also, when rodents get in it’s REALLY a mess. I’d take just a good vapor barrier and lots of air movement over the encapsulation.

Also, be aware of “plenum homes”. These have no vapor barrier and usually pea gravel on the ground. No heat ducts either - just one large supply blasting air into the space and register holes into rooms. At first glance it looks like a normal crawl space where someone forgot the vapor barrier and heat ducts.

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Until about ~5-10 years ago… just about everywhere in the nation this was indeed the case. How humid does it get up there in the summer? the whole idea is not to vent with humid air (it gets 95%+ humid here) in the summer as it defeats the purpose. Do you still inspect? what do you recommend, today?

And in my area, (FL), I never see vapor barrier or insulation. So venting is extremely important with the humid air. I have seen some major wood rot and mold from lack of air circulation


Do you see many crawl spaces in NY? What is typical in your area? Sounds like there is alot of opinions, solely based on locations


Yes, a lot of crawl spaces here, mostly partial. They are either vented, not vented, or partially vented. Those with missing insulation are usually okay, no problems. Those insulated with fiberglass insulation often have issues. Kevin has posted a link that every home inspector that inspects crawl spaces should understand.

We don’t get the crazy humidity like in the south so just passively venting is fine. Also, our bug problems really aren’t as bad as other areas. As an indication, HIs in Oregon/Washington are generally x-trained to do P/D inspections with the general HI. I’ve heard of some who don’t do both but always scratch my head and wonder how they stay in business. I’ve been doing both for 20+ years. The big/bad bug problems I find are usually accompanied by a wet crawl, a missing vapor barrier and vents that someone’s brother-in-law covered with plywood in 1960. Newer buildings with PT sills, something resembling a vapor barrier and a couple open vents and it’s usually okay. The absence of a lake under the house helps too but can be difficult here with all the rain.

I am surprised most people are recommending a conditioned crawlspace. In 5 years i have only see this once, although i suppose plenum crawlspace would be a better term. Seemed like a terrible idea, dead rats and droppings down there as you would typically find but that was directly their breathing air. Im in northern ca. Its dry here, humidity comes in the winter. If i found this crawlspace i would most likely recommend to vent it, install a vapor barrier if needed. I typically recommend insulation but that is a bit debatable. It has a minimal effect and can add to moisture problems. I know energy contractors in the area who will recommend to remove insulation and install vapor barriers.

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The conditioned crawl space should be sealed tight.


As Larry said, the crawlspace would be sealed so that no critters would be able to get in. Also, a conditioned crawlspace does not mean it is being used as a plenum. The few crawlspaces I have encountered had regular ductwork installed.

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