Timber and concrete upper floors

6.4.13Joists into hangers

Joist hangers shall provide a suitable bearing on the supporting structure and be of an adequate size, strength and durability.

Masonry supporting joist hangers should be checked for level and height. The top flange loading on the joist hanger should not be greater than the strength of the supporting masonry. Where joist hangers are supported on lightweight blockwork, the suitability of the hanger should be checked. Joist hangers which meet BS EN 845-1 have a stamp indicating the minimum compressive strength of block for which they are suitable.

Hangers should:

  • be detailed in the design, including the type of support to be used for joists, trimmers and trimming joists
  • have a 75mm minimum bearing on masonry
  • comply with BS EN 845-1 or comply with Technical Requirement R3
  • have performance equivalent to restraint straps at 2m centres where required to provide restraint
  • be the correct size for the joist or trimmer
  • be nailed through each circular hole in the vertical sides
  • bear on level beds and be tight to the wall
  • not be cut into the walling.

Joists should be accurately cut to length. Where joists are not built into brickwork or blockwork, blocking should be provided at the joist bearing. The blocking may be used for fixing plasterboard and floor decking.

Solid joists

Where connected to hangers, solid timber joists should:

  • have a minimum bearing of 75mm onto the hanger
  • be notched into the hanger to keep the ceiling line level
  • be the full depth of the hanger.

I-joists

Where connected to hangers, I-joists should not be notched at the flange, and should have:

  • a minimum bearing of 45mm onto the hanger
  • the tabs of the hanger bent and nailed to the bottom flange.

Hangers should be:

  • the full depth of the joist and restrain the top flange, or
  • at least 0.6 x the depth of the joist and have stiffeners (full depth) fixed to both sides of the web.

Metal web joists

Where connected to hangers, metal web joists should not be notched at the flange, and should have:

  • a minimum bearing of 75mm onto the hanger
  • timber uprights fixed between the flanges.

Hangers should be to the full depth of the joist and restrain the top flange, or another suitable means of restraining the top flange should be provided.