MINIMUM DIMENSIONS AND COVER FOR CONCRETE FOOTINGS WITH REINFORCING STEEL BUILD RIGHT Reinforcing footings cover Do you know the minimum bending diameter for reinforcing steel and its cover BY TREVOR PRINGLE, requirements in concrete footings? This determines the minimum width you ANZIA, BRANZ PRINCIPAL need to make your concrete footings. WRITER SOME DIMENSIONS GIVEN in NZS 3604:2011 Bending diameters 5 × bar diameter ● the bar diameter Timber-framed buildings for reinforced concrete For foundation walls to concrete slabs, the ● the bar bend diameter. foundation footings may be insufficient. This horizontal bars are typically D12 and the is due to the bending diameters and minimum vertical starter bars are R10. Two D12s stacked concrete cover required for steel reinforcing in Minimum bending diameters for reinforcing For a foundation non-cantilevered wall using concrete footings. steel are given in Tables 8.1 and 8.2 of NZS two D12s horizontally with R10s vertically, the 3101.1&2:2006 Concrete structures standard. minimum width (see Figure 1) will be: Footing widths in NZS 3604:2011 According to Table 8.1, the bending diameter ● cover on each side: 2 × 75 mm = 150 mm NZS 3604:2011 section 7.5 sets out require- for 6–20 mm diameter deformed and plain ● vertical bar diameter: 2 × 10 mm = 20 mm ments for reinforced concrete foundation walls steel reinforcing bars must be at least five ● minimum bend diameter: 5 × 10 mm = and footings for concrete slabs on ground. times the bar diameter. Therefore, the 50 mm. Figures 7.13(B), 7.14(B and C) and 7.16 (B and C) reinforcing bar minimum bending diameter This gives a minimum foundation width of give minimum footing width dimensions. However, for: 220 mm, which is 20 mm more than the details when the thickness of the steel and the bending ● R10 is 5 × 10 = at least 50 mm in NZS 3604:2011 specify. diameter are considered, the required concrete cover ● D12 is 5 × 12 = at least 60 mm cannot be achieved at the footing widths shown. ● D16 is 5 × 16 = at least 80 mm. Two D12s side by side If the bars in the base were installed side by Reinforcing steel needs 75 mm cover Minimum foundation width side, bars should be spaced apart by 50 mm When footings and foundations are poured To calculate the minimum width of a found ation to allow them to be fully encapsulated by the against ground (paragraph 6.11.3) or constructed or footing to meet the cover requirements, you concrete. The footing would then need to be at from unprotected masonry blocks, the minimum need to know: least 244 mm or 280 mm wide (see Figures 2 cover to the steel must be 75 mm. ● the cover on each side of the bent bar and 3). ground level R10 R10 2 × D12 with R10 2 × D12 50 mm gap 2 × D12 ground level ground level as as as required required required 75 mm 75 mm 75 mm 75 50 75 75 50 75 75 50 50 75 10 10 10 12 12 10 10 10 10 220 mm 244 mm 280 mm Alternate footing with two Foundation footing with two Foundation footing with Figure 1 Figure 2 Figure 3 stacked D12s. D12s side by side. alternate R10 starters. 28 — April/May 2016 — Build 153.