Quality.

    Structural spans and bearings — critical dimensions

    Bearings, notches, strutting and slab thicknesses for the load-carrying elements.

    Minimum

    Concrete cover to reinforcement cast against the ground

    75 mm cast against soil; 50 mm cast against blinding

    Reinforced foundations, ground beams and ground-bearing slabs.

    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

    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

    Ground-supported floor slab thickness

    100 mm

    Ground-supported concrete floor slab on hardcore

    Minimum

    Lintel end bearing length

    100 mm for spans up to 1200 mm; 150 mm for longer spans

    Masonry openings — confirm against the lintel manufacturer's schedule for the specific span and load

    Maximum

    Maximum depth of a hardcore bed under a slab

    600 mm

    Ground-supported concrete floor slab on a hardcore bed

    Minimum

    Minimum depth of a strip foundation

    450 mm minimum; 750 mm or more in shrinkable clay, deeper near trees

    Strip and trench fill foundations on non-aggressive ground, subject to the ground conditions on site.

    Minimum

    Minimum thickness of a strip foundation

    150 mm, and not less than the projection beyond the wall face

    Plain concrete strip foundations to Approved Document A.

    Range

    Permitted notches and holes in floor joists

    Notches: max depth 0.125 x joist depth, only between 0.07 and 0.25 of the span. Holes: max diameter 0.25 x joist depth, on the centreline, between 0.25 and 0.4 of the span, at least 3 diameters apart

    Solid timber floor joists — engineered joists follow the manufacturer's zones 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

    All critical dimensions · All topics

    These entries are our own editorial summaries of publicly available regulation. They are not building control approval, a warranty determination, or a substitute for the full source document.

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