Last time, we looked at how sister joists can help firm up a bouncy or sagging floor by providing support where the original joist has sagged. Here’s how to install the joist you’ve cut. We’ll assume the simplest situation, that is, with no jacking up of the floor involved.
First off, get a friend to help. The joist will be heavy, and you may need to have both ends raised at once.
First, figure out which joist or joists need sistering by estimating the location of creaking floors above, and by holding a level or line across the joists.
You don’t need to, but you may want to begin by zig zagging a bead of construction adhesive along the face of the original joist.
If you’re able to place the joist on the sill plate, insert one end between the floor and the sill plate. It may be a tight squeeze, though, so you have a couple of options. You can cut chamfers or a notch into the new joist to help get it into position. Do the same on the other end.
Once the joist is in position, hold it there with clamps. It’s tough to drive nails in those close quarters, but it’s a bit easier to use a screw gun. Drive three screws in every 16″ or so along the length of the joist.
Now go dance on the floor above.