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

problems with high fronted guttering meeting performance requirements, because of the way
slotted gutters had been specified as an overflow measure.
Drawing on public records from the Australian Building Codes Board, slotted gutters were for many
years the sole means mentioned for overflow in “Acceptable Construction Practice” and this was
most evident under Amendment 2, in the 1998 version of the BCA. This remained the case up until
the 2009 edition of the BCA when reference to slotted gutters was eventually removed.
Of note, the singular inclusion of this method during this period has been seen by the Committee as
sending a message to industry that slotted gutters were adequate on their own, without
consideration of other or additional overflow measures i.e. additional measures that may be
necessary in meeting the previously discussed performance requirement about not allowing water
entry into the building based on a 100 year ARI. At the core of this problem was the fact that slots
were specified in vague terms and did not include attention to size, spacing and location of slots; or
the difference in measurable overflow performance that each provides. For instance it is evident
that some high fronted guttering have significantly different slot sizes to others, thus making it
misleading to lump all of them together – especially given different ARI values across the State.
Though some may argue that “Acceptable Construction Practice” provides a degree of direction on
this issue – for instance, the “Explanatory information” at the end of Clause 3.5.2 which states that
“…in heavy down pours a slotted gutter may be inadequate” - it is notable that this text is for
guidance only (refer BCA Clause 1.1.8), hence reducing its impact and weighting of attention.
As a result, it can conceivably be concluded that those using slotted gutters under “Acceptable
Construction Practice” between 1998 to 2009 could argue that they met the BCA’s performance
requirements by virtue of meeting it’s own Deemed to Satisfy requirements, albeit that it is unclear if
such measures (slotted gutters alone) meet BCA performance requirements– especially the need to
prevent water entering the building based on the 100 year ARI.
On a more general note, it was apparent to the committee that many people using the BCA have a
limited understanding of how information is structured in it. For instance people regularly made
general reference to work being “BCA compliant” and though there is nothing in essence wrong with
this, it was at times apparent that such people were not aware of the difference between the BCA’s
performance requirements as opposed to “Acceptable Construction Practice” (which is purely one
option for Deemed to Satisfy construction). This has at times reduced the tenor of the debate and
thus the ability to resolve issues pertaining to high fronted guttering.
Of additional note, there is now virtually no guidance on appropriate overflow management for
gutters in “Acceptable Construction Practice” albeit that this is important to the ability of high
fronted guttering in meeting BCA performance requirements. It would be best to address this issue
by introducing a more measurable and purposeful approach to overflow management in
“Acceptable Construction Practice”.
9 Issues Concerning AS3500.3 and 3500.5
AS3500.3 and 3500.5 were the main options quoted by industry stakeholders used to comply with
the BCA’s performance requirements. Whilst both documents provide well defined calculation
procedures to determine roof catchment area, cross sectional area of eaves gutter, number of
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