How To Fix Sloping, Sagging, and Unlevel Floors

Old Wooden Floor
Old Wooden Floor. Getty / Gregor Schuster

When your floor slopes from one end to the other or has dips and sags, it is a frustrating, vexing problem that cannot easily be solved.

A bad window can be cured with a replacement window. A leaky roof can be fixed or replaced by a roofing company.

But when the underlying structure of your floor is bad, you will find that there are few floor specialists who deal with this kind of problem.

1. Floor That Slopes

Scenario: You have an old house with less-than-level floors.

In one bedroom, over a distance of about 15 feet, the floor slopes down 1.5 inches. Except for that slope, the floor itself is flat (not level).

Solution: For rooms that have a general slope, the issue may be foundation problems that require the assistance of a foundation repair company or a general contractor.

  • Foundation Footer Has Subsided: Since the floor itself is flat, the first guess is that the foundation footer has subsided or sunk. With foundation problems, this is an identifiable problem and you can actually find companies that specialize in foundation repair. They will have to come in and jack up that portion of the house and place new footers. While difficult to estimate the cost, certainly the cost will be no less than $10,000.
  • Sill Is Rotted Out: Alternately, the sill (the wooden part of the house that rests on the foundation footer) may have deteriorated either due to rot, water, termites, or carpenter ants. For this, you will have a harder time finding crews who specialize in this kind of work. Foundation repairs companies will not take the work, so you may have to resort to a general contractor, who will pull together tradesmen (or sub-contractors) for this kind of work. If you do not want to go through a contractor, a good general carpenter who possesses house jacks or is willing to rent them will be able to do this work, too.

    Keep in mind that anything involving 20-ton house jacks will take time. You cannot jack up a house in one day. It has to be jacked up slowly over weeks or even longer to avoid cracking wallboard, plaster, windows, and even structural elements.

    2. Floor That Sags and Dips

    Scenario: You have a dining room floor that, end to end is level, but between those two points are various sags and dips.

    Solution: Foundation may not be the problem. Instead, it may be an issue with joists and beams below your floor that require shoring up.

    • Sistering: If you have access to the basement or crawlspace, it is possible to jack up saggy joists until they are level and then sister them so that they remain straight after the jacks are removed.
    • Lally Columns: Another fix is to place adjustable steel columns under the joists to keep them propped up. This steel column fix does require that the base of the column be secured to the basement floor and the top of the column be secured to the joist.
    • Bridging: On the top side, another fix-it idea to lay down new hardwood over the existing floor. A plywood subfloor would nicely bridge any minor waves in the existing floor, and leveling compound would help, too. You will have to make sure your joists can handle the addition of considerably more weight from the plywood subfloor and 3/4" hardwood. Below, you can sister the joists and add a few adjustable columns to strengthen the joists to handle the additional weight.
    • Acceptance: One last idea is to come to terms with your sagging, sloping floor. Old houses often have floors that are less than perfect; even historic houses have saggy, sloping floors.