The house is about 26x26', the main support beam in the basement is 3x (2.5x7"ers) from 60 years ago set in the middle at 13', with 22" centers. The 3 beams are nailed together and look in reasonable shape. They are the main support for the whole house, on the main floor there is some sinking in the middle,n about 1/2" , both sides slop down toward the this main beam. So the beam must have come down 1/2" which i think is caused by the concrete degeneration on the supporting ends.
The beams ends sit on the concrete foundations of the basement, looks to be blocks and concrete. Then the main beam is supported by 4 steel posts grounded in the thick concrete basement floor. Look ok.
The foundation looks in good condition but there has been water damage over the years. I believe i have stop the water problem now. But the joyst has suffers some warping probably due to humidity.
Above the main beam on the main floor is a supporting wall then on the other end is a small bathroom underneath the staircase. So the bathroom and stair case sit above and on the main beam. There seems to be the most amount of 'sinking' is below the bathroom.
When you look at the bathroom floor you can see a bit of hump forming in the middle of the floor where the main beam is bellow and the side walls are pushing down. like a skate board park...
I think i need to support bellow at about 3 feet off of the main beam, supporting the bathroom walls and staircase.
i should be thinking of support each of the 13' joysts in the basement as well as the main beam near the foundation crumbling. Which is about 28 posts. That's why i'm think sister 2 (2x6's) as support posts should be $trong enough.
One the other hand it seems to be what is known as 'settling' of house but i think it is good time to think about preventive measures. The inspection i had mention doing this with jack posts. I have already fixed one crack joyst this way. What do you think about sistering all 13' joysts once i've propped them up with the new posts? overkill?