6.4.18 Notching and drilling
Notching and drilling shall be carried out within recognised limits.
Solid timber joists
Notching and drilling should be designed by an engineer where:
- the joist is deeper than 250mm
- it does not meet the guidelines in this chapter, or
- it is close to heavy loads, such as those from partitions, cisterns, cylinders and stair trimming.
Notching and drilling should:
- have a minimum horizontal separation of 100mm
- be in accordance with Table 6.
Table 6: Notching and drilling solid timber joists
| Location | Maximum size | |
|---|---|---|
| Notching joists up to 250mm depth | Top edge 0.1-0.2 x span | 0.15 x depth of joist |
| Drilling joists up to 250mm depth | Centre line 0.25-0.4 x span | 0.25 x depth of joist |
I-joists
Preformed holes should be provided in the web and:
- holes or notches should not be cut without the approval of the manufacturer
- restraint straps can be slotted into webs immediately below the top flange.
Metal web joists
In metal web joists:
- service conduits should run in the gaps between the metal webs
- maximum duct sizes should be in accordance with the manufacturer’s recommendations
- large service ducts may have to be inserted before fixing the joists, as it may not be possible after the joists have been fixed.
Last updated: 2nd January 2024