Tying up those slabs

One of several changes that came out of the Canterbury earthquakes was the requirement that all reinforcing in slabs-on-ground must be tied into the foundation wall reinforcing.

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Tying up those slabs
By
Trevor Pringle
Last updated 1 Dec 2011
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The Canterbury earthquakes of 2010 and 2011 and the research that was conducted after them led to some changes in how concrete slabs-on-ground are constructed.  

  • B1/AS1 2nd edition makes a number of modifications to cited standards: 
  • In Subsection 2.1.3 there are amendments around concrete slab reinforcement requirements in NZS 4229:2013 Concrete masonry buildings not requiring specific design  
  • In Subsection 2.3.7, there are modifications to the requirements given in NZS 3604:2011 Timber-framed buildings. These modifications remove the unreinforced and untied slab to footing single storey option In NZ 3604, as well as making other changes. 

The updated edition of NZS 3604 that is now available in draft form has a number of modifications that result from the Canterbury earthquakes.

A cross section diagram of grade 500E mesh reinforced slabs
Figure 1: Grade 500E mesh reinforced slabs.

Tying correctly

To tie the slab to the foundation, R10 starters at 600 mm centres are required. Starters should lap the mesh by 300 mm (see Figure 1). When installing the starters, the end embedded within the wall must be hooked around the bottom bars (see Figure 2).

Alternative to 500E mesh

While grade 500E mesh is now available in limited quantities, Figure 3 details a slab reinforcing option using bars.

A diagram showing starter bars hooked around bottom bars seen without the wall and slab
Figure 2: Starter bars hooked around bottom bars (wall and slab not shown).
A diagram of Slab reinforcing using D10 or D12 bars – an alternative to mesh
Figure 3: Slab reinforcing using D10 or D12 bars – an alternative to mesh.