Australia’s National Construction Code (NCC) states that certain performance measures need to be met when designing roof drainage. To do this, many factors including rainfall intensity, roof catchment area, gutter size/capacity, gutter outlet type (sumps, rainheads, nozzles), downpipe size, overflow planning and material selection should be considered, as they all affect overall drainage performance.
Adding to the complexity are variations to these requirements depending on what state you live in – these are good reasons then to leave roof drainage system design to a suitably qualified tradesperson, engineer or other industry professional.
Although there are variation requirements between the states, each reinforces that having adequate drainage is critical to protect people and the building from leaks or damage caused by water.
Fielders Rainwater Solutions Guides go into considerable detail covering a range of design topics including calculating roof catchment area, considerations for different roof styles and overflow measures.
Taking overflow safeguards as an example, many homes use high fronted gutters to hide the lower edge of tiles or roof cladding for a nicer finish. Where high fronted gutters are installed, the guides detail contingencies to avoid overflow back into the roof or building structure during heavy rain. To overcome this, gutters may feature a slotted front that allows water overflow, stop ends that that are cut to a lower level to encourage overflow over the sides, or by leaving space between the fascia and gutter back to allow overflow at the rear.
Alternative building design methods can also be used to get a similar result, and may include ‘Freeboarding’, where the gutter front is installed below the top of the fascia; removing lining from the eaves where the house design suits, or by applying ‘back flashing’, where gutter support brackets allow for back flashing installation such as external brackets.
Fielders’ Rainwater Solutions Guides also detail the minimum standard downpipe sizes to suit gutter types, taking into consideration variables such as downpipe style, effective cross section, diameter or shape.
Also included are tables that help simplify calculations such as for working out roof catchment areas, while making allowances for different roof pitches.
For installers, the guides are a powerful reference tool to help design and fit the roof and drainage system, particularly if using rainwater goods or working with roof styles that they’re not accustomed to.
And for homeowners, these brochures are a great educational resource, providing insight into the complexities of designing a compliant and effective roof drainage system, they’re just another way you can do it with Fielders.