Best way to insulate basement that shares crawlspace

[burgundywires]

Its actually our old house basement and we're kinda refurbishing it, The basement itself is pretty straightforward, but it shares an open gap with the crawlspace, the space isn't huge, but there's a little air passage between the basement and crawl and it kind of complicates things for me honestly. A part of me is thinking about just sealing it off completely but at the same time, I'm also thinking to leave it open and insulate around it so the whole area breathes together. I don't want to trap damp air or set myself up for mold issues, but I also don't want the basement sucking in cold crawlspace air all winter.
Has anyone done this and did you block off the gap and treat them as two separate zones, or did you insulate it in a way that keeps the basement and crawl connected but more controlled?

 

[C05mopolitan]

@burgundywires for a modern approach, I advise sealing off the gap and treating the basement and the crawlspace as two separate, insulated zones. honestly, the idea of letting them breathe together is an older, outdated method that often leads to more problems than it solves.

 

[purdil21]

@C05mopolitan makes a lot of sense
Close the gap with foam board or sealed framing, then insulate the basement walls properly and handle the crawlspace separately, either encapsulate it or vent it depending on your climate

 

[burgundywires]

@C05mopolitan if I seal it off completely, should I still put a vapor barrier down in the crawlspace? And do I need to worry about ventilation in there separately, or does sealing it mean it stays conditioned?
Thanks for chiming in too @purdil21