We just bought an 80 year old house and are fixing it up. The original wood floor is still intact - pine we believe. I haven't measured, but it appears to be the standard 3/4" tongue and groove planks throughout the house. It appears to be in good shape, although there are a few patches (perhaps they had to cut into the floor for access underneath the house as it is a pier and beam foundation). There is no sub floor underneath the tongue and groove. I've never dealt with a pier and beam house before. Is it normal to have the floor resting directly on the joists without any sub floor? There are some small gaps between some of the planks. Would it be sufficient to put spray foam insulation underneath the house? Or, do we really need to lay a new floor over the top? Thanks for your thoughts!
Julie

Any up north experts care to assist?

Pictures would help. But generally, in New England, some old homes either have plank floors top nailed to the floor joists or you find a 45 degree pine subfloor that is nailed to joists with some type of flooring on top of the pine.

Either way, if the floor feels solid , keep it . If you want to put something on top of it, do that .

To give better advice , I would need more information and pictures would be helpful

The old house I live in and the old house my son in laws, (both of them) there
is only a single floor) no sub floor and I have seen a number with just the tongue and grove fir flooring as the only floor, no sub flooring,
my house was built in about 1905, my one SILs house was built in about the same time, and the second SIL house was build in 1928.

A reasonably common practice in our area, for he time (home steading in Colorado in the early 1900's),

when I have worked on them and a new floor is wanted, I usually lay a Plywood underlayment, to level and reinforce the existing floor, if needed, and some depends on the type of floor that is being laid,

if the floor is in tact no reason not to keep it.

I have seen oak, tons of Fir and wide plank oak and pine laid directly over joists..Very common practice til about the 30s I would say..

I have seen a subfloor that looks like flooring with groves from homes built in the 1930.
what you can do is draw out the joist locations on the wall with a pen put 1/2 inch plywood over and install a new floor.