It’s probably tongue and groove fir like the others have said. Your profile doesn’t say what State you are in. This type of floor was common around where I am in California back in the 60’s and early 70’s. How is the weather where you are? I’m betting there is no insulation under that floor unless somebody has added it. I just did some work on a rental house my parents own that has the exact same floor. When we stripped out the carpet and some of the old underlayment you could actually feel wind coming up between those fir boards in places. I think the builder counted on putting wall to wall carpet over that floor and the carpet and pad acting at least as a little insulation. Just something to thing aboud.
-- Mark Smith, Tracy, CA., http://www.markscustomwoodcrafts.com
