There is no specific Deem-to-Satisfy (DtS) part in the National Construction Code (NCC) that provides details for the drainage of balconies, however consideration needs to be given to the relevant Performance Requirements that deal with Rainwater Management P2.2.1 and Weatherproofing P2.2.2 under Part 2.2 of NCC Volume Two and FP1.3 and FP1.4 of Volume One.
P2.2.2.1/FP1.3 Rainwater management requires that surface water resulting from a storm must not enter the building and must be conveyed to an appropriate outfall.
P2.2.2/FP1.4 Weatherproofing requires that a roof or external wall must prevent the penetration of water that could cause undue dampness or deterioration of building elements.
To satisfy the above performance requirements the NCC does reference Australian Standard AS 4654 Waterproofing membranes for external above-ground use Part 1 – materials and Part 2 Design and installation; through Part 3.8 Wet areas and External waterproofing and clause 3.8.1.3 External above ground membranes.
Even though these standards are about the materials and installation of an external waterproofing membrane, they provide the design criteria that needs to be considered to ensure that the waterproofing membrane system functions correctly and water can drain off the balcony.
There are a number of areas with AS 4654. 2 that make reference to the drainage of roofs, deck and balconies where an external waterproofing membrane system is installed.
Some of these areas include specifying the following:
Falls – Falls in finishes shall ensure that water drains to the drainage outlet. Falls should be no flatter than 1:100
Treatment at doors and windows where the inside and outside floors are level and an upturn can’t be provided – The membrane shall be fixed under the sill and terminate in the storm water system.
Clause 3.8.2.3 – there are details on the termination of the membrane at the gutter.
Clause 2.10 Drains – the membrane is required to be connected to the storm water drainage system.
Clause 2.11 – has details for overflows that should be directed away from the building
If you require assistance with technical matters or would like additional information HIA members should contact the HIA Building Services team on 1300 650 620
Craig Jennion
HIA Executive Director – Hunter