Guidance on reinforcement for concrete slabs-on-ground
This document is issued as guidance under section 175 of the Building Act 2004. This updates previous guidance issued in August 2011.
On this page
The recent changes to the B1 Compliance Document require that concrete slabs-on-ground constructed in accordance with NZS 3604:2011 on good ground be reinforced with a minimum of 2.27 kg/m2 of Grade 500E reinforcing mesh fabric which conforms with AS/NZS 4671.
As Grade 500E reinforcing mesh was not initially available, the Department issued two satisfactory solutions of equivalent capacity. One was based on a lower strength ductile mesh and the other on Grade 300E reinforcing bars.
Since then, the Department has worked with reinforcing wire and mesh manufacturers to ensure Grade 500E reinforcing mesh is available. A range of this reinforcing mesh is now widely available.
The two satisfactory solutions previously published (see below) may still be used if needed.
Back to top
Satisfactory solution: Equivalent Capacity Mesh
The steel properties of the mesh need to comply with the requirements of AS/NZS 4671, except that lower yield strength steel than that required for Grade 500E can be used, provided that an equivalent capacity in the slab is achieved.
- The amount of steel (kg/m2) necessary to achieve the equivalent capacity shall be determined as:
2.27 x 500 divided by the Strength Grade of steel (where the strength grade of the steel is the verified lower characteristic yield strength of the steel bar in MPa).
- The uniform elongation Agt (refer Table 2 of AS/NZS 4671) must equal or exceed 10%.
- Properties shall be determined in accordance with Appendix C of AS/NZS 4671. Testing shall be carried out by independent qualified testing organisations and evidence shall be presented to Building Consent Authorities and to others on request. Extensometer measurement taken across the necked portion of the test specimen shall be ignored.
- Reinforcing mesh fabric laps shall be a minimum of one grid wire spacing plus 50mm but not less than 150mm. Where deformed mesh wire with no cross wires is lapped with another sheet also with no cross wires, or where reinforcing bars are used, a lap length of 40 wire diameters or reinforcing bar diameters shall be required.
- Reinforcement must be supported on chairs to ensure reinforcement position and 30mm top cover is maintained.
- Mesh shall be suitably identified to confirm conformance with these requirements.
Back to top
Satisfactory solutions using reinforcing bars
Reinforce the slab using either:
- Grade 300E – D10 reinforcing steel bars (conforming with AS/NZS 4671) at 300mm centres each way with 30mm top cover, or
- Grade 300E – D12 reinforcing steel bars (conforming to AS/NZS 4671) at 450mm centres each way with 30mm top cover.
Back to top