NZ METAL ROOF AND WALL CLADDING CODE OF PRACTICE
SECRET FIXED CLADDING
11 V:2.2 PAGE 307
1 1 . 6 . 2 VA L L E Y S Fully supported valley gutters should comply with section 8.4.5. Where a valley is formed between two roof slopes, a separate valley gutter welted to the roof sheeting should be used. Jointing between the valley gutter and roof sheeting can be carried out by two methods:
• by dressing over a timber angle fillet with a single welt on the top front edge of the fillet. (see drawing 11.6.2.A) This detail is not suitable for high or very high design wind loads; • by forming a re-entrant fold in the valley to accept the panel turn under; (see drawing 11.6.2.B)
Timber angle fillet
Drawing 11.6.2.A
Drawing 11.6.2.B
Valleys should be secured using clips with a minimum of two fasteners, installed parallel to the valley, and be formed from at least the same gauge metal as is the valley metal flashing. Securing clips with two fasteners side by side, holds the clips in place more securely than using one fastener per clip because with only one fastener, cyclical thermal movement of the valley metal will loosen the fastener and the valley can bind against the misaligned clips. The back tab of a clip should be bent over the fastener heads, and the tab flattened, to keep the fasteners from backing out and from damaging the underside of the metal roof panel. Because valleys attached with clips can move within the clips due to thermal expansion and contraction, and slip downslope with time, the head of the valley should be securely attached to the substrate. A raised centre within the valley flashing not only allows for some expansion, but also prevents water flow from running across the valley from one side to the other. (see drawing 11.6.2.B.) Where a valley drains a dormer roof and the capacity of the panel or bay does not equal the discharge, it must be spread over two or more bays. (see section 6.5)
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