Early on in the process, we realized we were going to need to do some leveling work. Few, if any, of the floors in the house were level. Some tilted in multiple directions. This, we came to realize, was due largely to the failure of the mortise and tenon floor joists, many of which cracked at the tenon which drastically cut the strength of the member.
Our first solution was to hire a contractor, Phil, who came with with a 20-ton bottle jack, some 4 x 4 posts and his newly acquired puppy. He went down in the basement, I stayed on the first floor with a 4-foot level. I’d walk around and identify low spots. Phil would jack up the low spot while I watched the level. When the floor was level, I’d call out and Phil would place a post in the spot.
In some places, we raised the floor 2 – 3 inches before things were level.
It was exciting work, since the jack would slip occasionally and the floor would drop the 2 or 3 inches it had risen. Neither Phil nor the dog seemed the least bit disturbed by the crash.
While this method provided a generally level floor on the first floor, it didn’t do much for the second floor. And there were also spots against the back wall of the house where the floor rose sharply before meeting the wall. This mystified us for a while until we realized that the sill of the house, a massive 10″ square beam, had actually rotated several degrees, lifting the joists.
To fix these areas, we ended up tearing up the floor several feet back from the wall, shaving down the joists and beam as much as possible and reducing the subfloor to a single 3/4″ piece of plywood (the original house had two layers of 3/4″ boards. All this helped us to eliminate most of the slope. The rest we resolved by placing the kitchen cabinets there and shimming them appropriately.