A damaged broken or cracked ceiling joist can cause a ceiling to sag and should be repaired as soon as possible.
Roof joist fixing.
Squeeze the joist hanger tightly around the joist and drive the speed prongs into the ledger board to temporarily hold the joist in place.
Tack a beam under the sagging joists.
If the problem worsens it can cause the ceiling or upper floor to sag crack the drywall covering on the ceiling and compromise the structural integrity of your home.
Usually when a joist gets sistered the new lumber does not span the entire length of the old joist.
To replace the joist you need to measure the entire length.
If is wasn t for this joint a rafter or roofing joist would only balance on top of the wall plate making fixing difficult not to mention the fact that there wouldn t be any solid connection between the roof and the supporting walls below.
Jacking them up too fast may cause cracks in the walls and floors overhead.
Nailing two 2x4s together will work to span about three joists unless the sag is under a weight bearing wall.
Total costs will depend on the extent of the damage and the ease of access to the joists through a basement or crawlspace but in general sistering averages 100 300 or more per joist and could run 1 000 3 000 or more to repair a tilted wavy or bouncy floor under an average room.
To repair a roof joist you will need to either replace the entire joist or use a spliced in piece of wood.
Take some extra time and jack the damaged area up so that the new lumber doesn t need to be notched.
Place a level on the bottom edge of the joist to determine the amount of sagging that has occurred.
Repair and reinforce a ceiling joist by affixing a new plank to the side of the joist.
Cut a sister joist the same length as the damaged joist.
Remove any blocking or bridging above the sill or beam where the sister joist will go.
Birdsmouth joints cut into roofing rafters and mounted in place on top of the wall plate.
Set a hydraulic jack and post under the beam and jack up the joists about 1 8 in.
Keep in mind that the joist extends through the wall.
How to repair a cracked or sagging joist.
To fix the joists and rafters down on to the wall plates they should be toe or skew nailed to the top plate like below.
Set out the ceiling joists onto the wall plates the ceiling joists are installed before the rafters as they will stop the roof spreading and also give something for you to lay planks across to stand on when building the roof.
Identify the cracked or sagging joist before it causes additional problems.
Make sure the joist is sitting squarely in the joist hanger without gaps alongside and under the joist.
