34 — Build 143 — August/September 2014 DESIGN RIGHT BY ALIDE ELKINK, FREELANCE TECHNICAL WRITER, WELLINGTON IF AN INTERNAL GUTTER servicing a metal roof overflows, the only place for the water to go is into the building below, causing inconvenience and damage to the building and incurring repair costs. With a membrane gutter that is integral with a roof membrane, the risk from an internal gutter overflowing is lower. Good design principles Good internal gutter design includes: ● constructing gutters that are large enough to cope with the maximum rainfall intensity for the region ● lining the gutter with a continuous, impermeable material ● providing a good fall to outlets THE BEST WAY TO DEAL WITH INTERNAL GUTTERS IS TO DESIGN THEM OUT, BUT SOMETIMES, THIS ISN’T AN OPTION. WITH GOOD DESIGN AND CONSTRUCTION AND ONGOING MAINTENANCE, THE RISK OF AN INTERNAL GUTTER OVERFLOWING CAN BE MINIMISED. ● providing sufficient outlets so that, if one is blocked, another is able to discharge the full volume of water ● providing overflow outlets in obvious locations to give early warning of issues. Start with the Building Code There are three New Zealand Building Code clauses that must be applied to internal gutter design: ● Clause B2 Durability requires 15-year minimum durability. ● Clause E1 Surface water requires that construction protects people and other property from the adverse effects of surface water. ● Clause E2 External moisture requires that roofs: • shed precipitated moisture, hail and melted snow Figure 1 gutter base strong enough to walk on Internal gutter design. profiled metal roofing with 50 mm overhang to gutter Note: Other roof framing not shown for clarity. membrane gutter lining (or metal over isolating layer) additional 20 mm freeboard if required 70 mm minimum 300 mm minimum purlin gutter support structure roof underlay 100 mm minimum 50 mm roof overhang gutter sides to support membrane 20 mm H3.2 CCA-treated triangular fillets at base of 90° upstand DESIGNING, CONSTRUCTING AND MAINTAINING INTERNAL GUTTERS Internal gutters
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BY ALIDE ELKINK, FREELANCE TECHNICAL WRITER, WELLINGTON
IF AN INTERNAL GUTTER servicing a metal roof overflows, the only place
for the water to go is into the building below, causing inconvenience and
damage to the building and incurring repair costs. With a membrane gutter
that is integral with a roof membrane, the risk from an internal gutter
overflowing is lower.
Good design principlesGood internal gutter design includes:
● constructing gutters that are large enough to cope with the maximum
rainfall intensity for the region
● lining the gutter with a continuous, impermeable material
● providing a good fall to outlets
THE BEST WAY TO DEAL WITH INTERNAL GUTTERS IS TO DESIGN THEM OUT, BUT SOMETIMES, THIS ISN’T AN OPTION. WITH GOOD DESIGN AND CONSTRUCTION AND ONGOING MAINTENANCE, THE RISK OF AN INTERNAL GUTTER OVERFLOWING CAN BE MINIMISED.
● providing sufficient outlets so that, if one is blocked, another is able to
discharge the full volume of water
● providing overflow outlets in obvious locations to give early warning of issues.
Start with the Building CodeThere are three New Zealand Building Code clauses that must be applied to