Roof cladding: original details

Most houses of the 1940s-60s used tile or asbestos-cement sheet roofing, though some had corrugated steel roofs.

Concrete or clay tiles

Marseille or clay tiles were made in New Zealand from the 1940s through to 1959 (Figure 1).

Concrete tiles (Figure 2) have been manufactured in New Zealand since the late 1930s. They had a simpler profile and lacked the colour of the Marseille tile, but had the same durability and could be produced more cheaply. Installation and fixing was the same as for Marseille tiles.

The clay and concrete tiles are interlocking and were laid over battens and secured. The first state housing specification developed in 1936, was based on NZS 95, the original model building bylaw, which required that all roof tiles be individually secured so they could not slip in an earthquake. In the 1946 issue of the specification, this requirement was relaxed to apply only to alternate tiles.

Tiles were held in place on the roof by hooking the lug that was on the underside of each tile over the tile battens. Tiles were secured by 18 SWG copper or galvanised steel wire that was threaded through a hole in the lug and tied around the batten.

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Asbestos-cement sheet roofing

Asbestos-cement was easily moulded and therefore ideal for use as corrugated roofing. It was cheap, durable, easy to install and fire-resistant. A common trade name at the time was Super Six, which was available with accessories including ridge and hip cappings, barge boards, spouting and downpipes.

The corrugations of asbestos-cement roofing were wider and deeper than those of corrugated metal roofing, but it was installed and fixed in the same way. The sheets were 8’ (2.4 m) long and installed over building paper and wire netting that was laid over the purlins. Where there were three layers, one corner was cut off to allow the laps to sit flat. Fixings were with galvanised screws fixed through the tops of the corrugations. A metal washer fixed over another washer of bituminous felt made the fastening watertight.

Ridge coverings and other accessory components were screw-fixed in the same way as the sheets, and joints were made watertight with a mastic compound or similar material.

Due to the brittle nature of the sheets, the roofing substrate consisted of sarking, closely-spaced purlins or metal mesh laid over the purlins to provide additional support.

Asbestos-cement sheet roofing can be home for moss growth (Figure 3).

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Steel roofing

Corrugated, galvanised (zinc-coated) mild steel roofing, already with a long history of use in New Zealand, was not commonly used on state constructed dwellings during the 1940s and into the 1950s, but it was used more on privately built houses.

The typical thickness was 26 (Birmingham) gauge, i.e. 0.018” (0.45 mm), although 24 gauge, 0.024” (0.609 mm), was also available. Standard sheets were eight corrugations, 25½ ” (648 mm) wide and in lengths between 5-12’ (1.5-3.6 m) until longrun roofing became available during the 1960s. Longrun meant that roofs could be made from cut-to-length sheets without laps which are susceptible to corrosion.

The sheets were installed over building underlay and wire netting that was laid over the purlins. They were laid with a 1½ lap cover or, in exposed situations or when the roof pitch was particularly low, with a 2 lap cover. Fixings were with 2½” or 3” (63 or 76 mm) long, lead-head, galvanised nails, fixed through the tops of the corrugations. The exposed edge of the sheet would be laid facing away from the prevailing wind.

During the 1960s the range of metal roofing products increased with the introduction of metal tiles and tray section clip fixed roofing designed for use at much lower roof slopes.

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Flashings for roofs

Flashings for metal roofs consisted of 26 gauge, galvanised flat sheet steel, cut and folded to create the required shape to flash ridges, hips, barges, valley gutters, roof penetrations and changes in roof pitch where they occurred. Ridge and hip flashings to corrugated profile roofing had a lead soft edge for dressing to the profile.

At complex junctions of metal roofs, such as around pipe penetrations and chimneys, flashings were generally in lead and dressed over the corrugations.

Ridges and hips of clay and concrete tile roofs were formed with manufactured cap tiles mortar bedded to the tiles. Other flashings such as apron flashings were formed by dressing lead to the profile of the tiles.

Ridge and hip caps for asbestos-cement were mechanically fixed factory-moulded units in asbestos-cement with lapped joints.