All isn't as you think it is. For one they didn't have fiberglass 120 years ago so it has been installed since. Time to ask a smaller,younger and athletic person try getting underneath to look around.

Nothing is as simple as it sounds. I'd get a structural engineer, and look into the crawl space option.........and raising the house in total.

Klem, good point, not sure how they got it in, but trust me, there's no getting inside the crawl space currently. I'm not sure if raising it is an option either since it's a row house, so we share walls with neighbors on both sides.

Yours is a row house. That means it is attached to other houses. What have your neighbors done? How have they addressed the issues that you list? Perhaps a row house party, hosted by you, that “raises” these concerns??? (Sorry for the pun!)

I believe the International Residential Code requires a minimum of 18" between the bottom of the floor joists and grade. Since your house was built in 1890 I have no idea what your local jurisdiction would require if you replace the floor joists and subfloor. I would check with your building department to ask if they would require excavation of the existing crawlspace or not. Even if they don't require additional excavation but your decided to do it anyway I would definitely have some examine the building footings to see if they can withstand an excavation. Good luck and would love to know how things turn out for you.

Is there a possibility of blowinfgin insulation and as far as the joists are concerend you waill not know if they need replacing until you remove the flooring that is there . I agree ask the neighbors what they have done and IMo you should not have bought without knowing this since I have no idea how it passed inspection.

Consult with a structural engineer, if sections of the the current floor need to be removed for inspection - so be it. If you can afford the labor cost of hand-digging have it done. After the vapor barrier etc. a concrete floor, with 36 inches of headspace from the bottom of the joists, will allow tradesmen easy access (less cost to you on future hourly labor charges) and some surely needed storage space. Add an electrical outlet for portable lighting. With proper planning you might be able to relocate the HW heater. Many possibilities here.

Really appreciate the thoughtful responses! Good idea to ask around and get an engineer involved. I'll try to remember to post an update.

Those old row houses had REALLY shallow foundations in some cases- excavating 24” could go below the footer where I live. If the floor is failing pull the bandaid and rip it out from above. Option to pour a slab after?

You can't excavate your crawl without regard to support for the adjoining houses.

I've got all the pipes and other guts of the house down there

Installed by trained rats, I take it.

@worthy - When built in 1890 many row houses had a "privy" out back, the lone water supply (cold only) being at the kitchen sink. A hipbath was stored outside, then brought in on Saturday night and filled with water heated on the stove (coal-fired). With the advent of a sewer system, the privies were condemned and a hand-dug tunnel, just large enough for a small man to squeeze through, was dug to the interior point of connection. Being associated with the building trades in a major Northern city one gets to observe how things were done "way back when".