Adding On To Floor Joists

Most new construction uses 2 by 8 lumber for joists although 2 by 6.

Adding on to floor joists.

Tack a beam under the sagging joists. To add a finishing touch paint the new boards if they don t match the other joists. I read it doesn t need cross ventilation. The concept as explained used strips of metal about 1 1 2 wide about 1 8 thick and the length of each joist fastened to the bottom of each joist.

Then refurnish the boards and add new boards to the affected part. Building codes specify the minimum joist depth and spacing typically 12 or 16 inches on center for spans up to 20 feet but those requirements are intended to prevent plaster ceilings from cracking not to. Sistering is the process of adding a new joist next to each existing joist. It s kind of old school.

A neat trick contractors do when dealing with dry rot is add another level to the floor joists. So i ve got 2 6 floor joists spanning 15 feet. And i d like to know if i rip some inch plywood and sister it up against the 2x6s and glue and screw it if that would be sufficient. Notches will compromise the strength of the new joists but some notches are acceptable depending on their location.

But larger is not always better when builders are constructing a home or adding a room addition. Nailing two 2x4s together will work to span about three joists unless the sag is under a weight bearing wall. The extra two inches of vertical distance when a floor is framed with 2 x 10 joists rather than 2 x 12s can be quite important for example. In the case of 2x6 joists you can pair them up with additional 2x6 joists by nailing them together side by side.

If the attic joists are not adequate one way to strengthen the floor for live loads is to sister the old joists. They put chemicals in the affected board to kill the dry rot. Then set new joists same height as existing ones alongside the old. This solution doesn t make the floor as stiff as the other solutions but since it s relatively easy and inexpensive you might want to try it first.

The best way to limit annoying flex in a floor is to make sure that joists are sized correctly before a house or addition is built. After a lot of on line research i started seeing the same solution over and over adding to the bottoms of floor joists instead of sistering. Even if your joists already have a row of bridging at the center of the span adding a row on each side of the existing bridging will stiffen the floor. My crawlspace has six vents under the floor and i want to seal them up.