Add Floor Joist

Long spans of joists in newer homes may wobble or bounce from foot traffic.

Add floor joist.

When the sagging joists are level apply a generous bead of construction adhesive to the existing joist. The added depth of these two allows extra support and reduces bouncing. In the case of 2x6 joists you can pair them up with additional 2x6 joists by nailing them together side by side. Sistering is the process of adding a new joist next to each existing joist.

Then attach the sister joist using three 16d common nails driven every 16 in. Start by cutting out a small 1 2 in 2 5 5 1 cm section of the floor joist with a reciprocating saw. A sister joist is a second joist that goes alongside the first one and stiffens the floor. The floor above will be stiffest if you place the wall in the middle of the joists.

If the attic joists are not adequate one way to strengthen the floor for live loads is to sister the old joists. However shifting and settling can work these loose and separate the boards. 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. If you build a wall to support joists be sure to place a stud directly and tightly under each joist.

Driving 16d common nails in old hard wood is difficult. Ideally nails should be used to temporarily set the piece and then either lag bolts or more. In some cases additional joist supports will have to be installed before there can be extra heavy objects on the floor. The longer the distance a joist spans without support the more it will flex.

This will create a weak spot. Common sense tells you that large floor joists can carry more load and spacing joists closer together also increases the load bearing capacity of a floor. By building a wall under joists you divide the span. But it s usually best to run the sister joist over the entire span.

The only caveat to this is that you need to make sure you have enough space to add another joist. When sistering these pieces together it is easy to put just a few nails in the boards and move on. The joist support helps reinforce the floor so it can handle the weight load it needs to. The amount of weight that each floor joist handles is pretty amazing.

A joist support is the horizontal beam that supports the floor joists. Pry the floor joist from the subfloor with the back of your hammer. But larger is not always better when builders are constructing a home or adding a room addition.