Quality.
    Maximum
    England

    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

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

    Read the full answer

    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. All joists must be of the correct type, installed in the specified locations, and designed to incorporate suitably sized trimmers around floor openings.

    Basis in regulation

    How to check it on site

    Check joist spacing, type, and location against design drawings and ensure all floor openings have appropriately sized trimmers.

    Common failure

    Incorrect joist spacing or inadequate trimming around openings can compromise floor performance and structural integrity.

    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

    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

    Minimum

    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

    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

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