wow this sounds like my house on the other side of the country. I have the exact......seriously exact same thing. I'll write out some stuff maybe it will help. My crawlspace also is like a foot from the dirt to the joists and an addition to the main house that has a basement. I have no idea how they put the baseboard heat in that room.
My house is 120yrs old and this addition only has 2 feetof whatever rock they found on the property. It extends only 6" below grade. That was a big surprise.
Mine wood looks like yours after i stripped off 6 layers of flooring.....talk about a time capsule. But mine is straight grain fir not pine. I was told the only way to tell them apart is to cut them. I also have 2 layers of it instead of a traditional subfloor. I only found that because i had to cut through it for a frozen pipe. If yours looks the same on the underside but you can't see through it you probably have 2 layers as well.
Short of jacking it up and adding a proper concrete basement with height to move around, the only way i've come up with insulating would be to rip the floor up down to the joists, probably put in I-joists to get more height, add subfloor, then add that underfloor radiant heating stuff that is routed out to put pex heat in it, then the top floor. That way i'd have a heated and somewhat insulated floor. Doubt i'll do that ever.
https://www.warmboard.com/products/...vBuNvEL7KNSTSibCEoYXm66gcu1ve1xhoC4kAQAvD_BwE
Adding any insulation in the bays underneath (rockwool, fiberglass, etc) just seems to make a nice mouse motel. Even after you kill them their **** and piss are still there. God forbid if something bigger gets in there through those doors.
I took those doors out and sealed them up. I also repointed the foundation to keep the wind out. If you can get the lowest strip of siding up you can air seal with zip tape and/or zip caulking so the fountation to sill is sealed. you don't have anything in there now so big air leak area. General concensus I got when researching is to NOT sprayfoam the inside of the foundation if its rock. Those foundations will constantly be transmitting water in and out so sprayfoam increases the changes of mold.
Guessing those windows are double hung with ropes that go to weights in the side pockets. I've replaced just about all of mine over the last 30 years with anderson 200 series. IMO the most important thing is to get rid of those side pockets if you do. I increased the size of my windows and got rid of them. This of course makes interior drywall/trim and exterior work but something to think about. Replacement windows without at least spray foaming that whole cavity just isnt worth it.
When i drywalled this room......the 1st time lol.......i added 1.5" thick pieces of 2x4 to each actual 2x4 wall stud so i could have a true 2x6 cavity and add rockwool.
I get some heating down there from the baseboard heater pipes but if its single digits out that floor is freezing. I just put shoes on if i'm going to be in there. Consider a carpet for the winter that you can roll up in summer and store away.
