Sisterhood is powerful!
I only know one carpenter’s term that is feminist. It is the term for attaching a second floor joist to a cracked or under-built joist, beam, rafter, or stud. The term for this is called “sistering.” Sistering is powerful: it can stop sagging all over the house.
This is how it’s done.
- If both sides of the beam have wires and pipes near them, you might want a pro to do this job. Most do-it-yourselfers are not up to re-routing wires and pipes. Most floor joist will have one side you can work with.
- Nail a 2 X 4 perpendicular to the cracked joist, and run this to the joists on either side.
- Put glue in the cracks to help seal them as you initially support the lift the joist. Not so thick as to change the shape; this is an extra support for the weak spots.
- SLOWLY jack up the 2 X 4. The first day, jack it up until it is pushing at the subfloor. Then check it in a day or so. Jack it gingerly, no more than 1/8″ a day, if the joist is moving the subfloor above, lest you crack all your plaster upstairs.
- Once it is straight, cut a joist that is the same size. It should be long enough to cover the cracked part, plus 3 feet beyond the crack. Notch it where the original is notched.
- Glue the joists together. Clamp them until they are dry.
- Drive 3/8-in. x 3-in. lag screws every 16 inches through both joists. You will want to drill through first.
Buyers, when walking through a house showing, sometimes you’ll feel a sag halfway through the room. That is a cue for your agent to look at the floor joist below. Sometimes, they are cracked. Don’t panic, Sisterhood is here! Getting the joist re-supported with a sister joist will do the trick.
Joists that are not under supporting walls can be saved. It is not uncommon to see this and it is fixable without losing your shirt.
If the floors are compromised by weak main beams (the 4 X 4 that runs through the middle of most houses) or the cracked joist is under a wall, the problems is more structural and you should get help (and pay for it.)