Expert: Daniel Humphrey - 3/15/2009

Question
I live in a 1950's home 1000 sq. ft.  The wood floor has slight humps over the center support beam on center with the floor joists.  I ripped up the floor in where one of the humps are and saw that where two floor joists meet on the beam it appears that the end of the joist is pushing the floor up. It seems as though the outside end of the joist resting on the outside wall has settled more than the end on the supporting beam.  I attempted to jack the outside end of the joist up off of the outside wall to see if I could get some movement and improve the hump.  I could tell there was movement without any improvement at the point where the hump is.  I am thinking of shaving the top of the joists so they are even then laying new subfloor.   It seems as though there is no real good solution.  What do you think of my solution? What is the best and 100% way to fix this?  I am afraid that if I go through the task lowering center beam it will not solve the problem.   Please give me your overall analysis. (see attached document.)

Answer
Dear Leonard,

It is common for the outer supports to sink while the center support beam remains high, creating a bulge in the center of the floor. If the joists themselves are sagging, that can increase the hump at the summer beam.

Sometimes, the foundation supporting the outer walls have actually sunk into the ground, and sometimes the rim joists have rotted and collapsed. The faults can be remedied by cutting the old rim joists loose and raising the floor by hydraulic jacks and temporary saddle beams, actually raising the whole house. Usually, most of the work (besides the jacking) is done from the outside after removing some sheathing, just so you don't have to crawl around under there too much. If the rim joists are sound, the floor is raised by adding additional treated wood sills, or shims, on top of the concrete.

Lowering the center beam is definitely easier and will probably decrease the floor bulge. This option is good if the rest of the house has settled evenly and is okay. It is best to get a laser level on the job so you can eliminate guesswork. The best method of lowering the center (summer) beam is to place saddle beams beneath the floor joists about a third of the distance back from the summer beam and support them with concrete plinths having adjustable post bases. This will take the weight off the summer beam and allow you to re-position supports at the correct level and then lower the floor until the summer beam just rests solidly again. The saddle beams can remain in place at the new floor level.

If the entire house is fine, except the floor, you could just level out the existing floor as you have proposed. Or instead of removing the old floor and shaving the joists, you may use furring strips of various thicknesses running perpendicular to the joists. A new subfloor on  top of that would raise the floor and perhaps require shortening some doors.

I would check out the building a little better and determine how much the outer walls have settled and why. I would look for other damage and reasons for raising the outer walls back to level and then decide on how much I want to do to the building.

Daniel