High front guttering advisory committee report - NSW Fair Trading ...

BCA Date of
adoption
in NSW
Performance
Requirement
ACM (Standard) Acceptable
Construction
Practice
(ACP)
47
Explanatory
information
Comments
Original Explanatory Information (BCA 96 Amdt 0): Stormwater drainage systems specified in the Housing Provisions are not designed to remove all of
the water during exceptionally heavy rain, especially in tropical areas. Accordingly, it is necessary to design and install the system so that when overflowing occurs
any water is directed away from the inside of the building.
This may be achieved by using slotted gutters, locating the gutter so that it is below the top edge of the fascia or installing rainwater heads with overflow slots etc.
To enable the drainage system to achieve optimum capacity it must be cleaned and maintained on a regular basis, especially in areas where large trees overhang
roof drainage systems.
Special attention needs to be given to box gutters, valley gutters etc located above the internal areas of a building. In these situations if adequate overflow controls
cannot be implemented there may be a need to increase the size and capacity of drainage components to remove all water anticipated during heavy rain periods.
The design for such systems can be taken from AS 3500.3.
Amdt 4 Explanatory Information: Stormwater drainage systems specified in the Housing Provisions are not designed to remove all of the water during
exceptionally heavy rain, especially in tropical areas. Accordingly, it is necessary to design and install the system so that when overflowing occurs any water is
directed away in a manner which ensures it does not pond against, or enter into, the building.
This may be achieved by using slotted gutters, oversized gutters and downpipes, locating the gutter so that it is below the top edge of the fascia or the installation
of rainwater heads with overflow slots.
The installation of downpipes, especially near valley gutters, is designed to ensure rainwater from areas on the roof that have concentrated water flows perform
adequately. If downpipe spacings are to be increased, allowance for overflow should be considered.
Consideration needs to be given to box gutters, valley gutters etc located above the internal areas of a building. In these situations if adequate overflow controls
cannot be implemented there may be a need to increase the size and capacity of drainage components to remove all water anticipated during heavy rain periods.
There are many options available to designers using the requirements of the Housing Provisions. The designer will need to choose an overflow system that will
cope with the expected rain intensity, i.e. in heavy downpours a slotted gutter may be inadequate.