If the cut outs are too large or in the wrong location the joist can be weakened and unable to support the load it was designed for.
Cutting floor joists.
If you need to cut through a joist firm up the floor as shown in fig.
Sometimes joists are notched at the end where they bear on a wall or sill.
As a remodeling contractor and carpenter one common structural framing issue i see alot of in bathroom remodeling jobs are floor joists that were cut drilled notched or need to be cut out to accommodate plumbing pipes and drains.
Additional support for the floor joists is achieved by nailing the ends of the joists into headers.
Structural floor joist repairs.
Start by cutting out a small 1 2 in 2 5 5 1 cm section of the floor joist with a reciprocating saw.
These joists may need reinforcin g to reduce bounciness sagging or excessive deflection in the floor or ceiling.
Position bathroom vent fans so the ducts can run parallel to the joists right up to where they exit the house.
Then set new joists same height as existing ones alongside the old.
Make sure not to install joists so they run parallel to and directly under walls where you intend to install ductwork.
This will create a weak spot.
Nailing two 2x4s together will work to span about three joists unless the sag is under a weight bearing wall.
Then use pry bars and your reciprocating saw to pry and cut the floor joist away from the subfloor.
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.
Tack a beam under the sagging joists.
Framer jim anderson demonstrates solid techniques for cutting floor joists to length quickly and accurately.
Notches will compromise the strength of the new joists but some notches are acceptable depending on their location.
To minimize problems with ductwork.
Pry the floor joist from the subfloor with the back of your hammer.
Cutting and or removing joists to provide an entry or access can be the most difficult part of the overall project.
It is very easy to over cut the notches and remove the waste in two swift cuts but over cutting the notches in this manner weakens the structural integrity of the replacement lumber.
Section r502 10 of the international residential code states that header joists can be the same size as the floor joists when the header joist span isn t greater than 4 feet but if the header joist span is more than 4 feet you ll need to double the header joist and ensure that it s capable of.