I have a small farm house built in 1930 on a cement poured foundation with a crawlspace of only 12″ clearance. I’ve read a lot of articles about venting, conditioning, encapsulating but I’m not sure which applies best to my situation. The crawlspace has a dirt floor and had moisture damage along the sill which has since been fixed. It has never had any insulation or encapsulation or venting and is otherwise in relative good shape. The home does not have air conditioning. Does it make sense to encapsulate or insulate this older home’s dirt crawlspace considering it has held up relatively well in the past? It does get quite humid in the crawlspace and in NY we have cold winters and hot summers. There is no ductwork.
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I'm in the same situation with an 1840 house. The circa 1850s addition is on a non-mortared stone foundation (our land is sitting on a ridge of locally well-known sedimentary stone, Panton Stone), with a dirt floor crawlspace. We also have seasonal moisture that runs through the crawlspace. There's no way to divert the seasonal ground water because the ledge is on the surface right up against the house on the uphill side. The ledge goes into the crawl space, and on one side of the space the clearance is about the same as yours. I haven't figured out a way to insulate the half I can't crawl into, so it keeps getting moved lower on my extensive list of things to do. I've thought that simply insulating the walls (in my case I'd have to spray foam because they're stone) won't help a lot because the crawlspace floor will still be very cold, additionally because of the ledge. I've also thought about spray foaming the underside of the subfloor, a very expensive option, and no company will try in such a tight space. If I try to install rigid foam underneath the subfloor I still have the problem of how to fit myself and the foam into the space. I know none of this helps you, just commiserating, I guess. I've asked on a few forums in the past and some of the suggestions, even from "experts" like Martin Holladay and others, were somewhat silly: lift the whole addition and insulate, then lower it (yes, an "expert" actually suggested that), remove the entire addition's finished floor and subfloor, insulate from above and replace all of it (riiiiggghhtt). You said it's never had any venting, how would you access it then?
The most important task to to cover the dirt floor with 6 mil poly, sealed the best you can to the walls. You would need access to at least one side of crawlspace One way to do this in such a crawl space would be to attach a wood furring strip to one end and then push or better pull furring/plastic to other end. Also if there are any outside vents to the crawlspace seal them up.