Strutting rows by joist span

One row over 2.5 m span; two rows over 4.5 m

Herringbone or solid strutting, tight between joists and restrained at the ends

Every figure for this topic is on one page: Floor joists: spacing, bearing, notching and drilling

Read the full answer

Strutting stops joists twisting and shares load across the floor, and the number of rows follows the span.

Basis in regulation

Part A
Approved Document A
Read the source

How to check it on site

Check strutting is fitted before decking goes down — retrofitting it through a finished floor is impractical.

Common failure

Strutting omitted entirely, giving a bouncy floor that gets reported at handover.

Effective from 22 August 2026. Last updated 23 August 2026. This is our editorial summary of publicly available regulation, not building control approval or a warranty determination.

Related dimensions at this stage

Maximum

Light steel floor joist spacing and design

600 mm

Light steel floor joists should typically be installed at a maximum spacing of 600mm centre-to-centre, although wider spacings may be permitted if specifically engineered

Minimum

Floor joist end bearing on masonry

90 mm

Bearing directly onto masonry or a wall plate; joist hangers follow the hanger manufacturer's seating instead

Maximum

Floor deck fixing centres

300 mm at supported edges, 500 mm at intermediate joists

Boards laid with the long edge across the joists and joints staggered

Minimum

Lateral restraint for timber floors

90 mm

Timber floors can provide lateral restraint to masonry walls if joists have a minimum 90mm bearing onto the wall

Minimum

Lateral restraint for concrete floors

90 mm

Concrete floors offer lateral restraint to walls when they bear a minimum of 90mm onto the masonry

Minimum

Joist bearing and pointing

90 mm

Timber joists require a minimum bearing surface, typically 90mm, on supporting masonry or timber to ensure stable load transfer