How Do I Maintain Floor Joists?

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  • Written By: Dan Cavallari
  • Edited By: Bronwyn Harris
  • Images By: Itake Images, Gord Webster, Howard Sandler, Sven Hoppe, Design56
  • Last Modified Date: 08 August 2019
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Floor joists are the horizontal supports that hold up the floors in your home. Once they are installed, they usually do not require much of any maintenance unless they become damaged or exposed to mold and mildew. Squeaky floors are another indication that the floor joists may need some attention. If your floor sags, has a low spot, has a soft spot, or becomes bouncy, it is time to do an inspection of the joists to find out whether replacement or repair is necessary. In some cases, removal of the floor and subfloor may be necessary.

Maintenance for floor joists is usually fairly minimal, but if mold develops on the joists, it is best to address the problem as soon as possible. Joists that are in direct contact with soil, concrete, or other naturally moist materials are most likely to become moldy, as are floor joists that are situated near plumbing pipes in a basement. To address such mold, you can mix water and vinegar or bleach in a spray bottle and spray a fine mist of the solution onto the joists. Do not soak the joists; spray a fine mist and then wipe them down. Repeat the process until the mold is gone.


It is sometimes possible to visually inspect floor joists without removing the floor. This is usually possible if a crawl space or basement exists below the floor. An inspection may turn up a loose joist, a cracked or split joist, or even a warped support. If any of these situations arise, it will be necessary to either repair or replace the joist as soon as possible. For a loose joist, it is best to find where the support has come loose to determine whether it can be re-secured. A cracked joist may need to be replaced, but it may also simply be reinforced with a technique known as sistering.

Sistering a joist involves securing a new, straight joist to the old, cracked one. This is done by drilling holes and bolting the two joists together. It will be important to lift the floor or cracked joist to ensure the new joist is supporting the floor so it is flat and level. This can be done using a car jack or bottle jack, and a 4x4 piece of lumber. The same technique can be used for a warped joist. If the floor joists are damaged beyond safe repair, they will need to be replaced.


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