Improper Repair Of Floor Joists

In situations when sistering damaged floor joists with lumber of similar dimensions it can be easy to notch and slide the sister board into place.

Improper repair of floor joists.

A common but improper repair by other contractors is to install more full length joists. Improper holes and notches from alterations and running service lines are a major source of weakened joists. Take some extra time and jack the damaged area up so that the new lumber doesn t need to be notched. Position bathroom vent fans so the ducts can run parallel to the joists right up to where they exit the house.

However doing this does not fix the slant that the floor has taken since the old joists got damaged. 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. Jacking them up too fast may cause cracks in the walls and floors overhead. Floor is sinking between the floor joists.

Finally if all else fails drop your pipes and ducts down below the joists and box them in with wood framed soffits. A day until they re level. The notch was made where the floor joist recessed into a wood beam supported by chimney corbeling. Tack a beam under the sagging joists.

Improper notching can weaken a floor joist. Click the image to enlarge. Use common sense when deciding how many fasteners to use. Pictured is joist repair method for end rotted joist using plywood and some suggestions for best practice.

This will not work as the joist was not designed for this load originally. Corbeling is an old school overlapping arrangement of bricks with each course extending farther out from the vertical of the wall than the course below. Notches at the end of a joist should not exceed 1 4 of the joist depth. Generally there should never be any cuts or penetrations in the middle third of any joist or anywhere along the bottom of the joist.

Nailing two 2x4s together will work to span about three joists unless the sag is under a weight bearing wall. Set a hydraulic jack and post under the beam and jack up the joists about 1 8 in.