NCCv3 & AS3500.3 Compliance for Eaves Gutter overflow
Projects located in Victoria using Striproll gutters (except Half Round with cast brackets) require rear gap spacers to provide overflow where you are not using a method from AS3500.3 Appendix G.
The NCCv3 (Plumbing Code of Australia) requires that where high fronted eaves gutter is fitted, it must be installed with overflow measures that prevent storm water entering the building during a storm event with a 5 minute duration and 1% Annual Exceedance Probability [AEP].
Slotted gutter alone may not be adequate to provide the required overflow capacity for the storm flows from a roof.
It is the responibility of the qualified practitioner to assess each installation and install adequate overflow measures as a part of their project compliance certification to building authorities. This should be planned prior to installing High Front Eaves gutters.
In Victoria, there are 2 paths to compliance with the NCCv3 (Plumbing Code of Australia) overflow requirements - AS3500.3/HB114 and NCC Performance Solutions.
a) AS/NZS 3500.3 or HB114
VBA accepted "Deemed to Satisfy" example overflow methods are set out in AS3500.3 "Appendix G" and HB:114 such as providing a 10mm gap with spacers between the gutter back and fascia, fitting the top of the gutters front bead 25mm minimum below the top of the fascia board or installing a back flashing under the roof sheets to prevent backflow into the building. In Victoria, please refer to the VBA and their website for full VBA guidance.
Examples of overflow similar to AS3500.3 Appendix G:
Refer to AS3500.3 for full details.
b) A performance solution as described in the NCC.
Should the methods (described in item a) above) under AS/NZS 3500.3 "Appendix G" and HB:114 not be suitable for your project (such as when fitting gutter to steel fascia board), a PCA Performance Solution may be implemented and MUST be planned prior to installation and implemented to ensure water will not enter the building in accordance with the PCA and AS3500.3.
Implementation of a Performance Solution is the responsibility of the qualified practitioner. Assessment of overflow capacity requirements for a performance solution is particular to each job and will involve site specific items in addition to the supplied material's properties. Materials such as slotted guttering in themselves do not necessarily qualify a job as compliant. A Performance solution must consider the location specific rainfall, the size of the catchment, building design and the product fitment method. The performance solution must be designed by a suitably qualified person such as a roof plumber or hydraulic Engineer.
Striproll Eaves Gutters fitted to Steel Fascia Board may utilise 2mm gutter spacer clips to provide overflow capacity (which is rated by a qualified independent engineer) for use in a performance solution where suitable. Gutter spacers must be installed within Striproll guidelines to achieve the required overflow capacities to be used in your PCA Performance Solution and have compliance with AS3500.3. The 2mm spacer system has been rated with plain faced (un-slotted) gutter. Slots are not required to achieve the overflow capacity as tested.
You may wish to fit slotted gutter as an additional safeguard with spacers when hanging gutter to Steel Fascia Board.
2mm Gutter spacers may be utilised on timber fascias for Quad, Roundline and Feature gutter to provide the certified overflow capacity. Striproll Fascia Gutter is not compatible with 2mm spacers and must use an overflow method as set out in AS3500.3 Appendix G as described in point a) above.
Please consult the local Building Authority, your registered Roof Plumber or your Roof Drainage Designer regarding full details of compliance with the legislated requirements (including PCA/NCC performance solutions) to prevent overflow entering buildings.
Contact your nearest Striproll Sales Office prior to fitting your gutters for detailed information regarding product overflow capacities.
In States other than Victoria you may be able to rely on overflow solutions as set out in NCC Volume 2, contact your local authority to find out their requirements for compliance.