Gutters overflow half way between the downpipes - Gutter Pumper

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Q. Our downpipes are fitted at the end of the walls and the gutters overflow halfway between the downpipes during heavy rain. The builder has told us the gutters are compliant but others have told us the Building Code of Australia (BCA) requires downpipes to be no more than 12 metres apart.
Is this correct?

A. Prior to May 2007, the Building Code of Australia stated:
The spacing between downpipes must not be more than 12 m.

This was revised on the 1st of May, 2007 to state:
“ Downpipes - size and installation Downpipes must - (a) not serve more than 12m of gutter length for each downpipe;

As written, the BCA regulation allowed a 24 metre length of guttering to be served by downpipes fitted at either end.

When the BCA was revised on 1st May 2013, it again stated:
The spacing between downpipes must not be more than 12m.

Roof drainage is best installed in accordance with AS/NZS 3500.3:2003 Stormwater Drainage, a level 4a referenced document in the BCA but BCA level 4b Alternative Solutions are often used in lieu of the tighter Australian Standards (AS) that require larger gutters and downpipes serving smaller roof areas.

AS/NZS 3500.3 does not regulate a 12 metre maximum distance between downpipes.

But what does all this mean?

The BCA 12m rule means little as either the AS or the BCA can be quoted whenever suited as roof drainage DTS solutions can include mixes of both the BCA and the AS!


Plumbing practitioners in Victoria are required to install roof drainage installations in accordance with all of the following:

  • AS/NZS 3500.3 Plumbing and drainage Part 3: Stormwater drainage

  • The relevant section of AS/NZS 3500.5 Plumbing and drainage Part 5: Housing installations as prescribed in the National Construction Code Volume Three - Plumbing Code of Australia (PCA)

  • HB39 – 1997 Installation code for metal roofing and wall cladding

  • SAA/SNZ HB114:1998 Guidelines for the design of eaves and box gutters as prescribed within the Plumbing Regulations 2008

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