Master Plumbers May FAQs: Do you know the answers?

Every day the technical advice team at Master Plumbers answer calls from plumbers out in the field on a whole range of topics. Questions can range from interpreting standards to problems a plumber might be facing on a job to questions about licensing and registration.

This month we are looking at three roofing questions that commonly get asked of the team. How many did you know the answer to?

Q: Can we replace an original gutter installation despite it not being compliant with current standards?

A: The short answer is no.

There may well be a case for an installation that does not meet the current Australian Standards to be installed under a performance solution, particularly if that gutter has not had any issues with failure in the past but there is no provision in Standards, NCC/PCA or Handbooks (like HB39) that would allow for a like-for-like replacement.

So, if you are replacing a box gutter that is not compliant with AS/NZS3500.3 your options are:

• Complete a Performance Solution based on the existing size, etc of the gutter using the history of the installation as part of the performance criteria.
• Upgrade the installation to meet the AS/NZS3500.3.
• Contact the VBA with a view to repairing the roof.

Q: Can we install upside down pops in the box gutter or sump as an overflow provision?

A: No, to satisfy the provisions of the standards, we can only allow for overflow provisions as they are depicted in AS/NZS3500.3 and HB39. High capacity sump depicted in the adjoining image.

With box gutters you would have to use a correctly sized rainhead, sump with side overflow or high-capacity sump, to satisfy the overflow provisions that have been set out.

You can find what these should look like in AS/NZS3500.3:2025, Figure 3.7.3 Overflow devices - Box gutters.

Q: Can I connect my overflow back into the downpipe or storm water drain?

A: No, connecting your overflow back into the downpipe or drain defeats the purpose of the provision for overflow installed.

An overflow is installed to prevent damage or water ingress in case of a blockage to the downpipe or stormwater system.

This is why AS/NZS3500.3, clause 3.7.7.1 calls for the overflow device to discharge to atmosphere.

While we are on the topic of roofing, it is important to remember that when sizing sumps there is a minimum size according to the Australian Standards, regardless of the length you get on completion of your sizing calculations.

Minimum lengths:

• High-capacity sumps must be a minimum of 600mm in length (This can be found in figure H7, AS/NZS3500.3:2025, Appendix H)
• Sumps with side overflow, must be a minimum of 400mm in length (This can be found in figure H5, AS/NZS3500.3:2025, Appendix H)

These are just a sample of the variety of questions the team receives each and everyday. Access to the Master Plumbers Technical Advice team is just one of the many benefits that Master Plumbers (Victoria) members receive along with access to specialists in IR, HR, Health and Safety, as well as a range of discount and support from our commercial partners. For more information, please check out Plumber.com.au

Please note: The information above is based on the Australian standards. Please check with your local regulator and authorities for variations.