Repairing Floor Joists Cost

• If only a few joists are rotted primarily at the bottom, they can be repaired using a process known as "sistering" -- after the rot is cleaned away and the timber treated to prevent more problems, a new joist is laid beside the old one and fastened to it. Total costs will depend on the extent of the damage and the ease of access to the joists (through a basement or crawlspace), but in general sistering averages $100 -$300 or more per joist, and could run $1,000 -$3,000 or more to repair a tilted, wavy or bouncy floor under an average room.
• If the floor joists are extensively damaged, it will be necessary to support the house with jacks while the joists are removed and replaced. In many cases, the sill may also be rotted and need replacing. Costs can run $10,000 -$30,000 or more for a typical home, depending on its size, the extent of the extent of the damage and the ease of access to install jacks and replace the timbers. If the damage is limited to just one section of floor joists, the project could run $5,000 -$10,000.

• Joists carry the weight of walls, furniture, people, appliances and anything else placed on the flooring they support. Usually wooden floor joists are 2"x8", 2"x10" or 2"x12" timbers -- their size depends on their length, the amount of "load" they're designed to carry and the building codes in effect when the house was constructed. The Family Handyman explains how joists work.
• If there is sufficient access through a basement or crawlspace, floor joists can be repaired or replaced without significant impact on the rest of the house. However, if there is limited access, all furniture and appliances must be removed from the affected area and the flooring and subfloor torn out. The Family Handyman explains how to "sister" damaged joists and HammerZone.com describes using a jack to raise a slightly sagging floor.

• Floor joists can be damaged by boring insects such as termites or extended exposure to water. Before you replace damaged floor joists, you must exterminate the insects or improve the drainage and ventilation so the problem won't reoccur. Costs will vary widely depending on the extent and nature of the original problem.
• Typically floor joists are repaired or replaced working from below, in a basement or crawl space. But if there's limited access to the joists, it may be necessary to work from above, removing the flooring and subflooring to repair or replace any damaged floor joists. Costs will depend on the extent of the damage and the type of replacement subflooring and flooring chosen.

• Skilled do-it-yourselfers can sister floor joists with $200 -$500 worth of materials.

• ThisOldHouse.com provides tips for hiring a contractor.
• Get several estimates, making clear what is (and isn't) included in each quote. Request and check references; ask about the contractor's length and type of experience; and be sure they're properly bonded, insured and licensed in your state. See if there are any complaints with the Better Business Bureau.

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