(1) General.- Aluminium and aluminium-alloy roofing shall be protected from any dissimilar metal, and from concrete or mortar on which it may rest, by a layer of suitable bitumen-based or coal-tar pitch-based paint between the contact surfaces or by an insulating material approved by the local authority.

(2) Corrugated-aluminium roofing.- Corrugated-aluminium-alloy roofing shall comply with the following requirements-

a) where the corrugation pitch is between 65 millimetres and 80 millimetres and the depth of corrugation is 19 millimetres ± 1 millimetre, the thickness of sheet shall be not less 0,7 millimetre, and the maximum purlin spacing, measured centre to centre, shall be 1,2 metres for the 0,7 millimetre sheet;

b) the requirements for laps and minimum slope shall be as set out in paragraphs (a) and (b) of subsection (2) of section 16 for corrugated-steel sheets.

(3) Aluminium flat-sheet roofing laid in a deck.- Where aluminium or aluminium-alloy roofing in the form of a flat sheets is laid on a deck, the following requirements shall be met-

a) where the roofing is a single-layer weather-proof covering, the minimum thickness of sheet shall be 0,5 millimetre;

b) the deck shall be continuous and shall comply with the requirements of paragraph (c) of section 12, except that timber may be unwrought and butt-joints.

(4) Aluminium-foil built-up roof coverings.- Where aluminium foil is used for built-up roof-coverings on a continuous concrete or boarded deck, the following requirements shall be met-

a) where such a foil is used as a single-layer covering for a bituminous-felt built-up roof-covering, or where such foil is used in a built-up roof-covering of successive layers, the thickness of foil shall be not less than 0,05 millimetre and not more than 0,1 millimetre;

b) where such foil is used as a single-layer covering over concrete roofs or over bituminous felt on a boarded deck the thickness of foil shall be not less than 0,08 millimetre and not more than 0,1 millimetre;

c) the foil shall be embossed to ensure good adhesion and to allow for expansion;

d) the deck shall comply with the requirements of paragraph (c) of section 12, or be a shell-type concrete roof, steel-rowelled to a smooth finish after having attained its initial set;

e) when laid on a flat deck without bituminous felt, a minimum of two thickness of foil shall be laid in shingle pattern, with use of an approved grade of hot bitumen or cold adhesive;

f) when foil is laid on shell-type roofs, an approved cold adhesive shall be used. If only a single thickness of foil is required, there shall be a lap of at least 100 millimetres at any joint.

(5) Aluminium fluted-sheet roofing (long-span custom).- Aluminium fluted-sheet roofing shall comply with the following requirements-

a) the roof-slope shall be not less than 3 degrees with the sheets seam-bolted together at all side-laps with aluminium seam-bolts of not less than 6 millimetres diameter, and the minimum side-laps and end-laps of sheets and the maximum seam-bolting centres shall be in accordance with Table IV;

TABLE IV

b) where the roof-slope is less than 10 degrees, the end-lap shall be sealed with an approved mastic sealer