How to Level a Slanted, Sloping Floor

Old Wooden Floor
Old Wooden Floor. Getty / Gregor Schuster

Few aspects of a home elicit as much anxiety as a floor that out of level. When your floor slopes from one end to the other or has dips and sags, it is a frustrating, vexing problem that is difficult to make right again.

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. Before calling in a floor company or contractor, to give you an estimate, determine why your floor is slanting or dipping in the first place, along with common solutions.

When the Floor Slopes

Floor slopes and slants are common in old houses. A slant/slope situation might be one where, over the course of 15 or 20 horizontal feet, the floor slopes down one or two inches. Except for that slope, the floor itself might be flat.

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. Possible causes include:

  • 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. Foundation repair is always expensive and is rarely 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 repair companies will not take the work, so your best bet is to begin with a general contractor, who will pull together the right subcontractors 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 days or even weeks to avoid cracking drywall, plaster, windows, and even structural elements.

    When the Floor Sags and Dips

    Different from slanting/sloping floors are those that sag or have dips. For instance, you may have a dining room floor that, end to end is level, but between those two points are various sags and dips.

    Your foundation may not be the problem. Instead, it will likely be an issue with joists and beams below your floor that require shoring up. Solutions include:

    • 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. Sistering is the process of mating up two boards with nails or bolts so that the new board corrects or supports the other, weaker one.
    • Adjustable Steel (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 of the floor, another fix-it idea to lay down new hardwood over the existing floor. A plywood subfloor will 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 any floor coverings. Below, you can sister the joists and add a few adjustable columns to strengthen the joists to handle the additional weight.
    • Acceptance/Workarounds: Finally, many homeowners, when confronted with staggering bills for floor repairs, come to terms with their floors. Old houses often have floors that are less than perfect; even historic houses have saggy, sloping floors. Minor workarounds are possible, such as leveling individual elements within the floor (tables, armoires, cabinets, etc.).