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Insulating Unvented Crawlspace Connected to Conditioned Basement

njvictorianhome | Posted in General Questions on

Hi everybody!

First time posting, but this website has been invaluable for me the past year reading everything, so first of all- thank you all!

Last year I bought a home in northern NJ by the PA border. Soon after, I found plenty of moisture and termite issues in just one room in particular (the addition- more on that below). Remediating the home so far has included extensive grading (the soil had previously been so high that it overlapped the first piece of vinyl siding around the entire addition, so the corrective grading involved literally digging out all three walls of the addition) and rebuilding three exterior walls that had almost completely deteriorated from the termite damage.

The home was built in 1895 but the three walls with the most termite and moisture damage are from an addition built in the 1990s to extend the kitchen area. Most of the addition appeared to be built quickly and improperly when I inspected it prior to rebuilding the walls.

The home has a large fieldstone foundation with a large basement, but the addition is over a small concrete slab crawl space. The crawlspace is unvented but it opens up to the larger basement where I can crawl into the crawlspace from the opening in the basement wall.

The basement is conditioned with the HVAC, so my question is- since the crawlspace opens to the basement, should I treat insulating the crawlspace as if it was vented or unvented? I am primarily confused as to whether I should be insulating the walls/sill/rim joists or the floor joists and subfloor since this question seems to be based on whether the crawlspace is closed or vented- yet mine is neither.

Thank you!

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  1. DC_Contrarian | | #1

    If the basement is conditioned and the crawlspace is open to the basement then the crawl space is inside the building envelope and should be treated as unvented (closed, conditioned).

    In 1890 (and in some places as late as the 1990's) they believed in magic. By that I mean you could have a space like a basement or an attic that was sort-of kind-of inside the house and sort-of kind-of outside the house. So it would be unheated yet uninsulated and connected to the rest of the house. Today we believe in science, which tells us that space has to be either inside or outside the building envelope.

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