New Roofing Developed By School Of Architecture

Press, Volume XCIX, Issue 29219, 1 June 1960, Page 11

New Roofing Developed By School Of Architecture

[By a Special Correspondent]

A new style of roofing providing a satisfactory ceiling while keeping the advantages of indus-trial-type long-span sheathing and construction, has been developed at the Auckland School of Architecture. The style was described at the recent New Zealand Science Congress in Wellington by Mr A. H. Marshall, a senior lecturer at the school.

The roofing consists of a series of Bft 3in spans of trough-type aluminium alloy sheathing, with expanded-polystyrene sheet glued to its underside to form the ceiling. The trough sheet takes the place not only of the outside tile or corrugated iron weather-pro-tection, but also .of the rafters, ceiling joists, and such nogging as may otherwise have been required. The length of the spans

is controlled by the dimensions of the polystyrene board available. The polystyrene is made in Auckland in blocks Bft by 3ft by Ift, the required thickness of Jin being achieved by sawing or cutting with a hot wire. An experimental roof of this construction has been erected at the School of Architecture.

The thermal insulation provided by the new-style roofing in Auckland winter conditions worked out nearly twice as high as the minimum standard recommended for Auckland by the Department of Scientific and Industrial Research, Mr Marshall said. Traditional domestic roof types were well below the recommended standard in this respect. As the water-permeability of the expanded polystyrene was low. condensation should not be a difficulty in Auckland; but in

colder climates, where there was a greater difference between room and outside temperatures, the joints of the polystyrene sheets would have to be sealed.

The differential expansion between the polystyrene and the aluminium was unlikely to be a problem, as tests at the School of Architecture had shown that polystyrene had sufficient elasticity to take up any normal movement. No official fire rating of polystyrene foam had yet been published in New Zealand, said Mr Marshall, but he did not think there was any great danger. In any case, there was a non-inflam-mable board available for only a 10 per cent, higher price. Rainwater disposal was often a problem with aluminium sheathing; a “very satisfactory” solution developed at Auckland, however, used the trough section as the structural member with a folded gutter prop rivetted to

every second rib. Fall was obtained by skew-cutting the eave. The weight per square foot of the new roofing was only 0.871 b, compared with 3.81 b for corrugated iron and Gibraltar board and 111 b for tiles and fibrous plaster. The timber required for an iron roof with ceiling was nearly three times as much, and for a tiled roof nearly four times as much, as for the aluminium construction.

While no definite figures for a construction job could be given, it seemed probable, Mr Mafthall claimed, on the basis of the cost of the experimental roof at the School of Architecture, that the final roof would be of the same order of expense as a tiled roof and more than that of a corrugated iron -roof. The- extreme lightness of the new style, however, should make possible considerable economies in other structural parts of the building.