Understanding crawl space insulating

My nephew is building a house and it will have a crawlspace, he installed rigid styrofoam against foundation walls. From what I understand he says he is going to eventually lay down a vapor barrier when he is finished and insulate under the subfloor sheathing. If this is the approach he takes I told him he should have some sort of ventilation. My question is would he still need to knock out ventilation areas in the block walls if he did not insulate under the subfloor? but I am thinking regardless he should’ve had some sort of ventilation


Northeast Ohio is the location


I see windows

So the windows being installed is an acceptable ventilation as long as he keeps up on his remembering to operate the windows?

Just like a typical crawlspace vent, both can be in the open or closed position.

Do you think the most efficient way is to have his forced air and return supplying his crawlspace? As long as everything is insulated properly

During new construction, local building codes may require the addition of a sill gasket

Yes there was a sill sealer installed under the treated board, Is that what you are referring to?

I would rather to be able to operate the crawlspace vent from outside.

I would think there has to be some kind of air movement at all times, in Larry’s info it says to get the forced air and return air circulating through the crawl space. That seems to be the best approach, nobody wants the opportunity for pests to enter through foundation vents. Does it sound like I am think right on the subject?

I was only referring to some functions of crawlspace vents - they have very fine rigid screen as a protection from pests.
Definitely conditioned crawlspace is better.

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Yes, conditioned crawlspaces work well up in our Ohio, Michigan, etc. areas.

After inspecting by the AHJ, close and insulate the windows. And, around here one needs r-18 sill/rim joists and r-13 walls minimum…and don’t forget to foam the cracks.

Amen to that. Don’t vent the crawlspace and encapsulate it.

It looks like the answer is pretty straightforward (A conditioned crawlspace) thanks for the help.

You got it, Joshua. :smile:


Modern engineering and building experts are finding a non ventilated / non conditioned crawlspace can last longer and have fewer problems than a ventilated crawlspace if it is set up right. Vapor barriers, insulation between areas that may experience rapid thermal change including HVAC ducts, and humidity sensors are generally installed. I built homes for 25 years and a friend of mine was discussing this with me last year, and actually showed me two of his homes that are set up like this. I was sold, it is a solid concept.

I am in Colorado though, so you would need to check with some of the local experts in your area, considering you have higher humidity levels that may counter the benefits. Talk to a design engineer or two, a few phone calls should find one that is willing to discuss the concept with you.

Rick Moore, BA CPI
Sherlock Homes Inspection & Appraisal, LLC
Mead, CO

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