Roof cladding: original details

Original roof cladding was generally corrugated steel, flat-sheet metal, or built-up bitumen impregnated felt.

The extremely low roof pitches of parapet style houses meant that roof cladding options were limited to:

  • corrugated, galvanised steel roofing
  • flat-sheet metal roofing with welded joints
  • built-up bitumen-impregnated roofing felt (malthoid) laid over a timber substrate.

The flat-sheet metal roofing and bitumen-impregnated roofing were used when the roof pitch was less than 7 o.
Insulation was generally not installed in roofs, but there were often vents to provide roof space ventilation.

Metal roofing

Corrugated galvanised steel roofing

Corrugated galvanised steel roofing typically used in New Zealand was 26 (Birmingham) gauge, i.e. with a thickness of 0.018” (0.45 mm). Sheet sizes were typically 8’ (2.4 m) long and 25½ ” (648 mm) wide.

The sheets were sometimes, but not always, installed over building paper and wire netting. 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 2½ ” or 3” (63 or 76 mm) long, lead-head, galvanised nails fixed through the tops of the corrugations.

Flat-sheet metal roofing

Although rarely used, welded joint, flat-sheet metal roofing was an option. Flat-sheet metal roofing would have consisted of copper or zinc sheet metal and both would have required a fully supporting substrate.

Flashings for metal roofs

Flashings for metal roofs consisted of 26 gauge, galvanised flat sheet steel, cut and folded to create the required shape to flash shallow valley gutters (Figure 1), central gutters, and, less commonly, parapet upstands and caps.

Parapets may not have been flashed originally – it was more common for the roof flashings to be finished behind the stucco on the back of parapets.

A parapet flashing, where it was done, consisting of a folded metal flashing, carried up the inside face of the parapet for a minimum height of 6” (150 mm), fixed to the parapet framing, and folded a minimum of 4” (100mm) down across the roofing. A capping flashing over the top of the parapet wall was folded down the exterior face of the wall for a minimum of 2” (50 mm) and down the interior face of the wall to overlap the upstand flashing (Figure 2).

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

Architectural drawings of houses built in the 1930s do not specify parapet flashings but it is likely that it was assumed the roofer would flash over the parapet as well as the roof.

If the roofing material was copper, the flashing was copper as well.

Rainwater outlets, gutters and downpipes

Roofs with continuous parapets and a central, internal gutter drained to an outlet point or rainwater head. A single rainwater head was typical for a roof plan area of approximately 1100 ft2 (102 m2) but this was dependent on the roof configuration. The rainwater head was made from folded and welded galvanised sheet steel and located on the exterior face of  the parapet where the internal gutter was channelled through the wall.

A typical rainwater head was approximately 14” (350 mm) x 8” (200 mm) x 4½” deep (114 mm) with a 2½” (63.5 mm) diameter outlet connected to a galvanised steel downpipe.

Where the parapet was open on one side, a galvanised steel external eave gutter collected rainwater from the roof. It typically had an ogee profile and was fixed with external brackets to the fascia board. It was available in 8’ (2.4 m) lengths and was soldered on site to achieve the required length.

Rainwater downpipes were round, galvanised steel pipes, 2½" (63.5 mm) in diameter and supplied in 8’ (2.4 m) lengths. They discharged into a corrugated iron water tank, a soak pit, a stormwater system, or onto the ground.

Built-up roofing

Built-up roofing was a general term given to any continuously supported sheet waterproofing membrane. It was used in flat or very low-pitched (i.e. less than 10°) roof construction and always featured an internal gutter system.

The supporting substrate typically consisted of 1” (25 mm) thick timber boards laid over the rafters. An initial layer of felt that was not bitumen-impregnated provided a non-bonded layer between the roofing and the substrate.
A built-up membrane roof consisted of bitumen or asphalt-impregnated felt made from rags, cardboard, hessian or asbestos that had been soaked in bitumen, and were laid, generally in three to five layers, alternately with hot bitumen over a timber or concrete substrate.

Surface finish

The surface of a roofing membrane required a coating for protection against the effects of weather, ultra-violet rays and traffic wear in situations where the roof acted as a terrace or deck. The protective coating was generally a light-coloured or white fine aggregate or stone chip coating applied to the surface of the roofing membrane immediately following the application of the final membrane layer. Malthoid typically had a sand finish.

Alternatively, a reflective paint with a silver or metallic finish was sometimes applied. The painted finish reflected solar radiation, providing protection against ultraviolet light, but was not used where the roof also acted as a terrace as it provided no protection against wear.

Flashing at junctions and upstands

Membrane roofing junctions, such as at parapet upstands, required a skirting or turn-up of the membrane for at least 6” (150 mm) above the highest point of the roof. A timber backing board, covered with wire mesh for the membrane upstand to adhere to, was fixed to the framing of a timber parapet for a minimum of 6” (150 mm).

An angled fillet was required at all internal angles. For a timber roof substrate, a timber angle fillet was used and for a concrete substrate, a sand-cement fillet. The membrane upstand was protected by metal flashing carried over the top of the paprapet and down to lap over the top of the membrane skirting.

Depending on the height of the parapet, an additional layer of overlapping flashing could be provided; this would be turned into a goove and pointed for a concrete parapet and fixed to the framing in the case of a timber parapet.

Internal gutters and outlets

Internal gutters and outlets were formed in the same way as upstands. The gutter was framed and lined with a supporting substrate and fitted with angled fillets at the internal angles and a splayed top edge at the external angles. The base and sides of the gutter were lined with the roofing membrane to form a continuous membrane finish.

The internal gutter outlet was fully formed and lined with roofing membrane, angled fillets and splays for internal and external corners respectively, and was drained to a galvanised steel rainwater head as per the metal roofing internal gutter.

Edges and eaves

Where a membrane roof edge did not finish to a parapet, the membrane was finished with a rounded, turned down edge that was dressed over a timber batten to create a drip edge.

Roof outlets and penetrations

Asphalt was applied over angled fillets fitted to the base and internal corners at junctions between pipes and other roof penetrations and carried up the penetration for a minimum of 6” (150 mm). The top edge of the asphalt was overlapped by a protective collar.