Notching of Lumber Roof, Ceiling or Floor Joists
Notches made on the upper side of lumber joists near their ends (Figure 148) must be located within one-half the joist depth from the edge of the bearing and their depth cannot be more than one-third of the joist depth. Notches are not permitted on the bottom of joists. If notches are necessary elsewhere in the top of a joist, deeper joists must be used so that the net depth at the notch is equal to or greater than the joist depth required for the span and load conditions. The flanges of wood I-joists and truss chords and web members must not be notched or cut.
Drilled Holes in Joists
Holes drilled in joists must not be larger than one-quarter the joist depth or closer than 50 mm (2 in.) to either edge (Figure 149). Holes in engineered wood products must conform to the product manufacturers’ guidelines for size and location.
Notching and Drilling of Studs
Load-bearing wall studs that have been notched or drilled to more than one-third of their depth must be reinforced (Figure 150), usually with 38 mm (2 in. nominal) lumber nailed to the side of the studs and extending at least 600 mm (24 in.) on each side of the notch or hole. Also use reinforcing when notched partition studs have less than 40 mm (19⁄16 in.) of solid wood remaining.
Notching and Drilling of Top Plates
In load-bearing walls, top plates must be reinforced with 38 mm (2 in. nominal) lumber when the solid wood remaining in the plates is less than 50 mm (2 in.) in width. If required reinforcing must be placed on the face of the plate or stud, sheet metal may be used to support the wall finish and to protect the plumbing and electrical wiring from gypsum board fasteners.
Roof trusses cannot be notched or drilled.
Source : Canada Mortgage and Housing Corporation (CMHC)