Any Carpenters by trade?

[Citizen229]

Any US based carpenters? Seeking some advice on span tables.

Im going to be redoing some pre-1940's sections of my house floor. They are actual 2x8's 18" on center. To replace these floors and use 2x8(16" centers) will put me at the limit of 40 loads for span. Sooo.. Im, going to have to cut down 2x10's to 8" width. With the extra 3/4" inch over a 2x8, is there a span table that show the span for going outside of standard dimensional lumber? I would prefer not to assume the extras 3/4 inch thickness will put me well under the limit of my span.

I am guessing they knew when they built this house the floors were not correct. The 2 front room have large limestone rocks, chiseled flat on top, with block laid on top.

[stormryder]

Im, going to have to cut down 2x10's to 8" width.

The extra 3/4 would make the joists stronger but you may find it easer to use normal 7 and 1/4 2x8s and use 3/4 shims (use 1x4) under the joists where they sit on the foundation/beams. Getting a full 8" joist under the exterior walls may be nearly impossible especially if the joists you are replacing are rotted or even just slightly soft. Joists tend to crush a little between the walls and the foundation sill.
If the old joists are sound you could just add new lumber to strengthen the floor to desired load capacity.
Ripping out the old joists is really an ambitious project and expensive.

I am guessing they knew when they built this house the floors were not correct. The 2 front room have large limestone rocks, chiseled flat on top, with block laid on top.

This is under the floor for support?
If so you may have to add a beam under the joists to break up the span.

[Citizen229]

Yes the rock slabs are for support. They share a common beam spanned between them.

These front rooms are the most screwed up . The load bearing walls do not sit on block, they sit next to block. For these walls they used 4- 2x8's to make header to hold the weight over the span. Needless to say those will be monolithic untill the original L shaped roof and 2 expansions comes off. There is a tremendous amount of roof weight as it stands, the large L shaped roof is old style, with 6" slats under rolled single, and god knows how many layers of modern shingles. One of these "off center load headers" is going to get a load bearing wall(to concrete basement floor) under it to get support as well as provide a wall for a new staircase to the basement. The other is between the 2 front rooms. This "beam" has the joists of 1 room hanging on it. This joists set is going to get turned run the opposite way to remove floor load from the beam to block on both ends. This beam is the sagging beam, causing uneven floor. I got a few sheets of steel painted up and some floor jacks ready for this beam. The floor will get leveled, plaster be darned.

[stormryder]

Quite the project, if you do rip 10s down to flush up the basement ceiling I wouldn't worry about the extra 3/4. It will actually increase the load the floor will carry and getting some of the roof load transfered directly to the basement floor will defiantly help prevent any sagging in the future. I wish you the best of luck.

[Citizen229]

thanks for the support! (pun intended ). The new staircase is not the sagging one, but correct, it will help over all.