Do you have access to the underside of the floor boards? On our fir subfloor, the boards are actually marked with the name of the lumber yard, which might narrow it down a bit. (Of course, the floor could have been replaced without replacing the subfloor, though!)

As far as the pattern, no clue---but it does look like those are matchstick boards (narrower than traditional floorboards, usually just under an inch). You see them in some California homes built in the 20s and 30s, but I don't know if they were popular other places at the same time.

You are all losing me on the sub-floor talk. I've never had an old house with a sub-floor. What you see in the basements are the bottoms of the tops you walk on upstairs and they're all thick and substantial.

You have a relatively modern floor if done some what unusual. How are the floors in the remainder done?Don't think I have seen that pattern before. IMO, houses of that era would have had wider plank flooring, perhaps yellow pine or similar. Over time,pine floors get a lot of dings. Presume the previous owners removed the original flooring.

I was thinking maybe it was from the 20s or 30s, as my last apartment (which was built in the 20s) had a wood floor of an almost identical width, though it didn't have the same pattern and did have some inlay. My house was restored/added onto significantly in the mid 1940s, though, so it's possible the floor could be from that time.

I'll have to go in the basement and see if I can find any kind of subfloor. I'm not sure if the original floor was removed, or if it's underneath the floor you see in the photo. At the top of the stairs on the second floor, where the original staircase meet the new floor, it actually looks like the new floor is right on top of the old. I am sure I'll never, ever be able to convince my SO to tear up a perfectly good floor to expose the old one underneath, but boy, it would be great to still have that original floor intact somewhere!

In the 'newer' old houses where I've lived, the early 20th century ones had subfloors of boards laid diagonally; both had narrow oak strips for the actual flooring but not in a design like yours.

Argh! Is it just me??
Lol! :-)
Your description of the pattern on the floor, then the link to the photo had me anxious to see it, it sounded pretty cool and like a lot of work potentially went into it. Then... the photo - with a rug covering up the most interesting sounding part? And no-one else mentions it?

All teasing aside, can we get a pic, without the floor-covering? Perhaps I'm just missing something, lol - I'm known for that. The color tones in the wood do look lovely, and seem (to me - not an expert by ANY means) to have a warmth and depth that new wood might not give off if not done "just so".
If it were me, I'd embrace them and move on to the next project. If ya think you don't have any more, and you're in an old house - just wait a few days, lol!

Ha, sorry about the rug. I have been meaning to ask this question for ages, but wouldn't you know it, my beloved camera is completely dead and I won't be getting a new one for a while yet. I thought maybe, maaaaybe someone here would recognize the floor pattern as something they have in their own old home and could jump in and say, "Oh of course, that's an X pattern from 19??"!

I went in the basement last night to see if I could find any kind of a subfloor above the ceiling beams. I did see boards of about 4-5" in width, and I got excited for a second because they appeared to be about the same color as my home's staircase. Then I walked over to the "new" part of the basement, above the "new" addition ("new" = 1947) and there it was, the same subfloor I had just seen in the original section of the house. Darn! So, I guess the original floor isn't underneath after all, at least not on the first floor.

I believe the pattern is called a yankee floor. I have seen this pattern many times. Almost always w/ maple on the perimeter and fir in the middle.One instance that I recall was the main house built around 1840 and the other house , on the same property 1920's . I have a justifiable suspicion that the carpenters added the floors to the older home while building the other house.Most of the older houses I have seen had random width soft pine that was painted.I am just N of Boston and there are no shortages of older homes here.

Since you found the same subfloor underneath both additions, then the floor probably does date from the latter period...but it is weird to do that style that late.
A floor like you describe usually had a larger center section than 4"x4" made of cheaper wood because it was meant to be hidden by a rug, thereby saving money. The expensive flooring was laid around the edges of the room just as you describe--I believe this was done mainly in New England, but don't hold me to that. :)
Perhaps your house's original floors were laid like that, and when the addition was done, they redid all the floors to match a similar look?

Update. My suspicions were correct. The two houses were owned by a friends great uncle who was a carpenter from Nova Scotia.
The 20's house was built by him and the floors in the older home were added by him.
I just came from another friend's house, same exact pattern.But it was all maple. This house was built in 1905 and these are the original floors.
As far as the sub floors go, I vacationed in New Brunswick this summer and noted the arrangement at my buddies' house. 45degrees as a opposed to being laid perpendicular to the floor joists like we do in the US. I had been told many years ago by old Norwegian carpenter that this was done for structural integrity (wind shear) . Not only the sub floor but the sheathing also.
As far as the addition goes from the 40's, the builder decided to go with what was there. Ply wood did not really come to use until the 60's. The house I live in was built in 1959 , there is no ply wood.