Galvanised steel, aluminium, and metal or concrete tiles were all common for roofs during the 1970s.
As with wall cladding, a wide range of roof claddings became available during the 1970s (Figures 1 to 4). Most common were concrete tile, metal tile with a stone chip finish, and corrugate profile galvanised mild steel.
Other options available included:
- corrugated aluminium roofing
- tray or trough section galvanised mild steel roofing with concealed fixings
- organic asphalt shingles
- trapezoid metal roofing profiles
- clay tiles and slate (on more expensive houses)
- corrugated asbestos-cement sheet roofing
- asbestos-cement shingles
- butyl rubber and asbestos/bitumen (Nuralite) membrane roofing
- translucent polycarbonate, acrylic and fibreglass roofing to porch and veranda roofs
- aluminium glazing bar systems with wired or toughened glass.
Roofing underlay consisting of heavyweight bitumen-impregnated Kraft building paper was supported by galvanised wire netting where purlins or metal tile battens were used. It was not commonly used when concrete or metal tiles were installed.
Insulation was not commonly installed in houses until NZS 4218P was issued in 1978. See Insulation.
Sizes and profiles
During that decade, roofing manufacturers adopted metric measurements with the introduction of high tensile 0.40 mm G400 grade and 0.55 mm G 300 grade roofing and new profiles such as tray and trapezoidal profiles.
Longrun roofing had become available during the 1960s, and meant that roof cladding could be made from cut-to-length sheets without the need for end laps which were susceptible to corrosion.
Some older imperial roofing may still have been used such as 26 (Birmingham) gauge, (that is, 0.45 mm), although 24 gauge, (0.024" or 0.609 mm) was also available. Standard sheets were 8 corrugations, 648 mm wide and in lengths 1.5-3.6 m until longrun roofing became available.
Tray section roofing fixed with a concealed clip nailed to the purlin was commonly used on roof slopes of less than 8⍛.
Sheets were laid over Kraft building underlay and wire netting over the purlins.
They were laid with a 1½-lap cover, or a 2½-lap cover in exposed situations or when the roof pitch was particularly low, and sheets were laid so the exposed edge was facing away from the prevailing wind.
Fixings were by means of 63 or 76 mm lead-head nails or spiral shank galvanised nails with a metal/neoprene sealing washer fixed through the tops of the corrugations.
Galvanised steel roofs were generally painted on-site or left unpainted, and side laps were primed.
Pre-painting of galvanised steel roofs steel was not introduced until 1982.
Flashings for metal roofs
Junctions and changes in direction of the roof such as ridges, hips, barges, valley gutters and changes in roof pitch, were flashed with 0.55 mm G300, galvanised flat sheet steel, cut and folded to create the required shape with a lead soft edge for dressing to corrugate and trapezoidal profiles.
Flashings were notched for tray section, or the ribs were cut and capped.
The use of tray section saw a different approach to flashing changes in direction where the roofing pan was folded over the junctions and the ribs cut and flashed with proprietary cap flashings, sometimes called Canterbury prickles (Figures 5 to 7).
Flashings at complex junctions such as around pipe penetrations and chimneys were generally in lead, which could be folded over the corrugations - and in some instances soldered to the roofing.
Aluminium roofing was available in two sheet widths with eight and ten corrugations respectively, as well as in tray and trapezoidal profiles. It was installed and fixed in the same way as corrugated steel roofing, but with aluminium-alloy nails and washers fixed over neoprene washers.
Pressed metal tile roofing had its origins during World War 2 when a process was developed in which mild steel was coated with a specially-developed protective bitumastic emulsion coating, which was then covered with sand. The coating was initially applied to corrugated steel, but a pressed tile profile (from 0.55 mm G300 steel) was soon adopted, and stone chips replaced the sand. The roofing was able to be laid to a lower roof pitch than standard tiles - as low as 15° - while still providing a lightweight roof.
The tiles were nailed to 50 x 50 mm or 50 x 40 mm timber battens fixed over the rafters and the lowest course of tiles was supported by the fascia board, which was raised to keep the bottom row of tiles at the same angle as the other tile courses.
Purpose-made flashings were provided for ridges, hips and gables, while at apron flashing the edges of the tile were bent up on site and cover flashed.
Concrete tiles (Figure 8) were durable, low maintenance and economical to install. They could be laid on roofs where the pitch was greater than 20°.
They were laid over 50 x 50 mm or 50 x 40 mm timber battens and held in place on the roof by a lug on the underside of each tile that was hooked over the batten (Figure 9).
Alternate tiles were also secured with copper or galvanised steel wire threaded through a hole in the lug and tied around the batten. To increase stability in exposed situations, tiles were also sometimes bedded in a cement mortar.
Proprietary ridge, hip and gable trim tiles were mortar bedded to the roofing tiles. They were available in a range of colours and with accessories that included ridge and hip tiles, apex caps and end stops.
Corrugated asbestos-cement roofing had a long history of use, was durable and did not ignite easily (although it would explode when very hot). The health risks of asbestos were not yet well known, so it was a commonly used roof cladding.
A well-known trade name was 'Super Six'. This was available with accessories including ridge and hip cappings, barge boards, spouting and downpipes.
Although the corrugations of asbestos-cement roofing were wider and deeper than those of corrugated metal roofing, it was installed and fixed in a similar way.
Sheets were available in 2.4 m lengths and installed over building paper and wire netting laid over purlins or sarking. Where overlaps created three layers, one corner was cut off so the laps could sit flat.
Sheets were fixed with galvanised screws fixed through the tops of the corrugations with a metal washer over a bituminous felt washer to make the fastening watertight. The ridge cap and other components were screw-fixed in the same way as the sheets and joints were made watertight with a mastic compound.
Because the sheets were brittle, purlins were more closely spaced than was necessary for other roofing materials, or roofs were sarked. See Roof framing.
Membrane roofing or walk-on roof decks were generally laid over plywood, but a moisture-resistant particleboard which was available briefly in the 1970s was also used. This did not prove to be durable.
Membranes during the 1970s were typically:
- butyl rubber, a flexible, impervious, synthetic rubber that was developed during the 1950s. Butyl rubber was typically 1.5 mm thick and supplied in 1200 mm wide rolls and fully adhered to the substrate. Joints were lapped secured with adhesive or lap tape
- bitumen asbestos roofing, consisting of bitumen reinforced with asbestos fibre, marketed under the trade name Nuralite. It was available in 2400 x 900 x 2 mm sheets and laid using heat to spot adhere it in a staggered sheet pattern with 75 mm lapped side and end joints.
The 1970s also saw the arrival of elastomeric liquid applied membranes, but initial use was more typically in commercial buildings.
Flashings for membrane roofing
Membrane roofing junctions such as at parapet upstands required a turn-up of the membrane for at least 150 mm above the highest point of the roof, and an angled fillet was required at internal angles.
Internal gutters and outlets were formed in the same way as upstands with the gutter framed and lined with a supporting substrate, angled fillets at the internal angles, and generally a splayed top edge at the external angles. The base and sides of the gutter were lined with the membrane to form a continuous finish.
Corrugated translucent polycarbonate and fibreglass sheets to match the corrugated roofing profiles became available and were installed where additional light below was required. Additional purlins were sometimes required to provide mid-span support for the sheets.
Thermal movement of translucent sheets tends to be greater than other roofing materials and over time UV exposure causes loss of translucency and reduced strength. Sheets are brittle and should not be walked on.