6.4 Timber and concrete upper floors

6.4.15 Strutting

Strutting shall be provided where required to distribute loads and ensure adequate rigidity of the floor structure.

Strutting should:

  • not project beyond the top and bottom edges of joists
  • be firmly blocked to the wall at the end of each run
  • be provided before the deck is laid.

Proprietary metal strutting should comply with Technical Requirement R3.

Solid timber joists

Strutting to solid timber joists should be:

  • provided in accordance with Table 4
  • be herringbone (38mm x 38mm timber) or solid (minimum 38mm thick and 0.75 x the depth of the joist).

Table 4: Strutting for solid timber and I-joists

Joist span (m)Rows of strutting
Under 2.5None needed
2.5-4.51 (at centre of span)
Over 4.52 (at equal spacing)

I-joists

Strutting to I-joists should be:

  • provided in accordance with Table 4, where required.

Metal web joists

Strutting to metal web joists should be:

  • provided in accordance with Table 5
  • solid timber ‘strongback’ bracing.

Table 5: Strutting for metal web joists

Joist span (m)Rows of strutting
4-81 (at centre of span)
over 82 (at equal spacing)

Last updated: 2nd January 2024

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