TAS Part E3 Stormwater - Roof drainage systems

The objective of this part is to—

1. safeguard people from illness, injury or loss (including loss of amenity) due to the failure of a roof drainage installation; and
2. ensure that a roof drainage installation is adequate; and
3. conserve water and energy; and
4. safeguard the environment; and
5. safeguard public and private infrastructure; and
6. ensure that a roof drainage installation is designed and is capable of being maintained so that throughout its serviceable life it will continue to satisfy Objectives (a) to (e).

Buildings are to be provided with roof drainage to provide protection to people, property and the environment from adverse effects of stormwater.

(1) A roof drainage system must have the capacity to transfer the volume of water anticipated in a 5% annual exceedance probability rainfall event.

(2) Box and valley gutters must have capacity to transfer the volume of water anticipated in a 1% annual exceedance probability rainfall event.

(3) The annual exceedance probability must be appropriate to—

1. the importance of the building; and
2. the severity of potential damage to the property; and
3. The severity of loss of amenity, illness or injury that would result from the failure of the system.

A roof drainage system must provide an overflow device suitable for a 1% annual exceedance probability rainfall event.

All internal roof drainage components must be watertight.

(1) A roof drainage system must ensure that—

1. stormwater is transferred to a Network Utility Operator's stormwater system or an approved disposal system; and
2. appropriate access is provided for maintenance and clearing blockages.

(2) A roof drainage installation must avoid blockage and uncontrolled discharge causing—

1. loss of amenity; and
2. loss to building and property.

(3) A roof drainage installation must avoid foul air and gasses accumulating in the roof drainage system.

Performance Requirements E3P1 to E3P4 are satisfied by complying with E3D2 and E3D3.

A roof drainage system must comply with—

1. AS/NZS 3500.3; or
2. Housing Provisions 7.4

(1) When a liquid trade waste generating process does not fully occur within a building, suitable roofing must prevent the entry of stormwater to the disposal system.

(2) When a liquid trade waste generating process occurs within a building where one or more sides are open to the weather, a vertical overhang of a minimum of 10° from the roofing must be provided.

(3) Where the wind driven rainwater is likely to enter under the roof in extreme storm conditions, the roof must overhang by a minimum of 10° from the roofing.