Also see:
6.66.4.16 Joists and openings
Upper floors shall have adequately sized and properly supported trimmer joists around openings.
Trimmer, trimmed and trimming joists should be:
- detailed in the design
- designed in accordance with Technical Requirement R5.
Connections between joists should be made with suitable ‘timber-to-timber’ hangers, and:
- where face fixing I-joists to another I-joist, be provided with backer blocks on both sides of the web of the trimmer
- where metal web joists are used as a trimming joist to support another metal web joist, have timber uprights between the flanges of the trimmer.
Deflection
The following should be considered in the design and detailing around openings in floors:
- Deflection of trimming joists to be similar and no worse than the adjacent floor joists
- Compound deflection of the floor including trimming and trimmed joists should be limited to the overall floor deflection, to ensure there is no differential movement or noticeable step in the floor level adjacent to the trimming joists
- Where partition walls are built off trimmers and trimming joists, particularly fire compartment walls, additional care should be taken to ensure that the overall deflection of such joists would not result in residual gaps at the heads of the walls or in distorted walls or openings within the walls.
There should be no notching or drilling of trimmers or trimming joists unless proven by design calculations.
Last updated: 2nd January 2024