(1) Roof-coverings.- All roofs and roof projections of buildings shall be weatherproofed and shall be covered with one or more of the coverings detailed in this Part.
(2) The coverings shall be secured so as withstand climatic conditions, such as wind pressure, wind suction and changes in temperature.
(3) Notwithstanding the restrictions placed on the profiles and sizes of roof coverings in sections 13 to 21 and the B.S., S.A.B.S. and C.A.S. mentioned therein, alternative profiles and sizes of the respective materials may be used, if approved by the local authority.
(4) Substructure.- The trusses, rafters, purlins or other supporting framework to roof-coverings shall be designed in accordance with the respective requirements for concrete, steel or timber, contained in these by-laws.
(5) Timber battens and purlins shall be provided of such strength, dimensions and spacing as shall adequately support the roof covering applied to them, together with all superimposed and wind loads, to the satisfaction of the local authority.
(6) Roofs with more than one kind of covering.-Where a roof-covering is provided over another roof-covering, the minimum roof-pitch shall be taken as the minimum pitch allowable.
(7) Flashing.-Flashing shall be provided so valley and the junction of roofs with chimneys, parapets and other abutting surfaces, so as to render the roof weatherproof, and such flashings shall comply with the following requirements-
a) they shall be corrosion-resistant;
b) they shall be composed of soft copper, zinc, aluminium, hard lead, galvanized metal, asbestos-cement or other approved material having similar corrosion-resistant qualities. Zinc flashings shall have a mass of not less than 4 kilograms per square metre, and lead flashings of not less than 15 kilograms per square meter. The minimum thickness for flashings of copper, galvanized metal or aluminium shall be 0,55 millimetre. Asbestos cement flashings shall be at least 5 millimetres in thickness;
c) whenever a metal flashing or other metal fitting is used in conjunction with a dissimilar metal, whether of the roof or another fitting, which may lead to electrolytic corrosion between them, provision shall be made to prevent such corrosion by painting on contacting surfaces wit bitumen-based paint or by any other method which will prevent a galvanic couple being formed;
d) flashings to the junction of roofs with chimneys, parapets and other abutting surfaces shall be in two pieces. The underneath flashing shall extend at least 100 millimetres up vertical surfaces and shall be covered with the second flashing which shall be securely wedged and pointed.