By today’s standards, art deco roof framing was undersized.
Roof framing typically consisted of 4 x 2” (100 x 50 mm) rafters spaced at 18” (450 mm) centres. In a ‘butterfly’ roof with a central gutter, they span between the parapet wall framing and the central gutter in a ‘butterfly’ roof; in a mono-pitch roof, they span between the front wall parapet framing and the rear wall framing.
Support, where required, was provided by 4 x 3” (100 x 75 mm) or 4 x 2” (100 x 50 mm) struts that transferred the load to a loadbearing internal wall.
The roof framing was significantly undersized by today’s standards.
As with villas and bungalows, there were also marked regional variations in art deco construction.
If the roof pitch was between 7 and 10º, the cladding was typically corrugated galvanised steel, which was fixed to 3 x 2” (75 x 50 mm) purlins on the flat spaced at 36” (900 mm) centres, or sarking.
The very low-pitched and deck roofs, i.e. roofs where the pitch was 1 – 7º, were clad with a built-up membrane laid over sarking. The sarking consisted of 1” (25 mm) thick, close-butted boards that could be laid perpendicular to the rafters or on the diagonal.
Roof bracing was not generally incorporated in roof framing of very low-pitched roofs. A butterfly roof with valley rafters had some roof bracing provided by the triangulation created by the valley rafters, but no roof plane bracing was included.