Foundations: original details

Foundation walls

A continuous, in situ, reinforced concrete foundation wall supported the timber subfloor and wall framing (Figure 1). Where reinforced concrete wall construction was used, the walls were cast continuously with the perimeter foundation wall.

Foundation walls were typically 6–8” (150–200 mm) thick supported on a 12” (300 mm) or 18” (450 mm) wide x 6” (150 mm) deep footing. The underside of the footing was a minimum of 18” (450 mm) deep. The above ground height varied according to ground slope. Foundation walls supporting single storey timber framing were typically reinforced with one ½” (12.7 mm) diameter reinforcing bar at the top of the wall and 2 x ½” (2 x 12.7 mm) diameter reinforcing bars in the footing. A 4 x 2” (100 x 50 mm) timber plate was cast into the top of the concrete wall (or bolted to it) to provide fixing for the floor joists. Bearers were sometimes supported in recesses cast into the foundation wall or, alternatively, half-piles were cast integrally with the foundation wall. Damp-proof membranes were not always used in subfloor construction in this period. Where a reinforced concrete wall was continuous with the foundation wall, the foundation wall was typically 6–10” (150–250 mm) thick, supported on a 12” (300 mm) wide x 6” (150 mm) deep footing – and a minimum of 18” (450 mm) depth to the underside of the footing. Reinforcing consisted of 3 x 3/8” (3 x 9.5 mm) or 2 x ½” (2 x 12.7 mm) diameter reinforcing bars in the footing and 3/8” (9.5 mm) diameter reinforcing rods at 12” (300 mm) centres both ways in the walls. Bearer support consisted of a reinforced corbel or a reinforced half pile cast integrally with the foundation wall to support the bottom plate where it ran parallel to the foundation wall.

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Subfloor ventilation

Subfloor spaces were fully enclosed and ventilated by means of wire mesh or concrete cast grilles spaced evenly around the foundation wall. Access to the underfloor space was often limited or effectively non-existent.

In some situations there may have been insufficient ventilation grilles to provide adequate ventilation under the floor.

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Sloping sites

Housing on sloping sites sometimes had high foundation walls and subfloor jackframing to create the level platform on which to build. On steep sites (for example in Wellington), the construction during the 1930s generally included levelling the site. ‘Cut and fill’ excavation techniques were used, where the site was excavated to create a level building platform and the fill deposited elsewhere on site to create an area of flat section.

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In situ concrete, continuous foundation walls were finished on the exterior with a solid plaster finish. Splash coats were common, in fan or radial patterns. Piles By the 1930s, precast concrete piles were readily available. They were typically 8 x 8” (200 x 200 mm) square, unreinforced concrete. Piles were arranged in rows generally 4’8”–6’6” (1.4–2 m) apart and at centres supporting bearers at 4’6”–5’6” (1.350–1.650 mm). The requirement for strengthening against earthquakes meant that each pile was tied to the bearers with a loop of No. 8 wire. Concrete piles sometimes had galvanised ‘rodent proof’ caps designed to prevent rodents climbing into the subfloor.