Floor joists are horizontally oriented beams that make a frame for building up a raised floor.
Typically, they are spaced 16 inches apart on center. Some may be spaced 12 or 24 inches apart and supported by exterior walls and interior load-bearing walls.
Floor joists are typically solid sawn from wooden 2×8, 2×10, or 2×12’s.
They must be precisely spaced otherwise you’ll end up with sagging or uneven floors. They are normally set perpendicular to any load-bearing walls.
Even with the best support, floor joists often flex. Doubling the number of joists will double the floor stiffness.
Before you add significant weight to the floor, such as installing new granite counter tops, check whether the floor joists need additional support to safely hold it up. They can be built up to meet just about any need, within reason.
Silent floor joists can ensure a quieter floor, when properly installed.
If you’re experiencing sagging, uneven, or squeaking floors, there can be any number of root causes.
During original framing some of the floor joists may not have been straight or were slightly bowed over the full length. If installed without proper blocking, they can twist and warp below the subfloor, causing an uneven floor.
Floor deflection is more common in older homes because the floor joists often are smaller or spaced farther apart than in modern homes. They often aren’t on 12- or 16-inch centers, so they allow too much “give” when you step on the floor between the joists.
Maybe your foundation is drooping and the whole house is sagging, or just the effects of time and gravity is catching up to them.
Again, in older properties, floor joists may drop at one end because the wood has rotted and become compressed.
Internal load bearing walls often have less in the way of foundation and may have settled more than the external walls, or joists have warped under the load of heavy furniture over many years.
Repairing Floor Joists
Depending on your situation, there are several approaches to correcting these problems.
Nailing solid blocking between floor joists can strengthen the support for subflooring, eliminating squeaks.
They can be “bridged” with 2×10 blocking or X-braced wood slats or metal straps, to support heavier weights in a particular area of the house and prevent bending and twisting (or buckling) of the joists.
A good way to stabilize floor joists in a crawl space is by “sistering,” or attaching new boards the same size as your existing joists to double their width.
In extreme cases (particularly with crawl spaces or unfinished basements) where the floor joists are all in distress, running a new beam crosswise the length of the house supported by new columns can do the trick.Allied Foundation and Crawl Space is ready to assess your foundation issues and provide a customized solution. Give us a call at (256) 580-3210.