Can you provide Crawlspace Insulation Design Assistance?

Randy Christensen
Updated: Aug. 27, 2020

Be warned; this is a long post!  Apologies in advance.

I live in the colder climate of western Massachusetts in an 1830s vintage home.  We have a 4'6" crawlspace (approximately 18' x 26') beneath our wood floored living room.  The house foundation is piled-up field stone (typical of that era) and it can be drafty in high winds).  The crawspace is dirt floor with several cemented fieldstone pillars supporting the original floor joists (full 8"x4" chestnut and oak petrified!).  Old, unfaced fiberglass batts were installed by a previous owner in the 24" o.c. joist space and secured with wire hangars.  The batts are in various states of sagging including several sections that have completely fallen out of place.  The basement adjacent to the crawlspace contains our oil-fired heating system; there is a small opening allowing access to the crawlspace from the "full" basement (still fieldstone and dirt floor, but about 6'2" of headspace).  My problem is the cold living room floor AND humidity issues as well. 

I was thinking of new fiberglass batts in the 24" o.c. joists supported by one of the newer breathable foil membrane products stapled to the underside of the joists; I was planning on securing the membrane with firring strips to get a better seal and to prevent the fabric from tearing away from the staples.  I was then planning on the 6 mil poly install on the entire crawlspace floor.  We do have some electrical and heating utilities within and beneath some of the crawlspace joists so spray foam would be problematic (I also have heard some spray foam horror stories that make me cautious).  I would cap off my efforts with a continuous running dehumidifier in the basement.  I am fortunate to have a drywell port which I can direct the dehumidifier drainage into easily.

Any comments on my plans would be greatly appreciated.  I'd be happy to add photos if they would better help to visualize my situation.

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