NCC 2019 Amendment 1 Public Comment Draft

The minimum pipe cover requirements in NCC 2019, V2 clause 3.1.3.5 Stormwater Drainage appears to conflict with the requirements of AS/NZS 3500.3:2018, table 6.2.5

With reference to NCC 2019 V2, part 2.2 Damp and weatherproofing, clause P2.2.1 Rainwater Management:

a) Surface water, resulting from a storm having an average recurrence interval of 20 years and which is collected or concentrated by a building or sitework, must be disposed of in a way that avoids the likelihood of damage or nuisance to any other property.

b) Surface water, resulting from a storm having an average recurrence interval of 100 years must not enter the building.

c) A drainage system for the disposal of surface water resulting from a storm having an average recurrence interval of—
(i) 20 years must—
(A) convey surface water to an appropriate outfall; and
(B) avoid surface water damaging the building; and
(ii) 100 years must avoid the entry of surface water into a building.


Would perhaps better worded as:

a) Surface water, resulting from a storm having an average recurrence interval of 20 years must be collected and disposed of in a way that avoids the likelihood of nuisance or damage to any buildings or land.

and,

b) Surface water, resulting from a storm having an average recurrence interval of 100 years must not enter any building or adjacent land.

and,

c) A drainage system for the disposal of surface water resulting from a storm having an average recurrence interval of—
(i) 20 years must—
(A) convey surface water to an appropriate outfall to prevent nuisance; and
(B) avoid surface water damaging the building; and
(ii) 100 years must avoid the entry of surface water into any building or adjacent land.

It is not clear exactly what "property" is. I feel this would perhaps be clearer is written as "adjacent land".

The recommended change to draft is suggested to better reflect current "engineering industry standards" (in SA at least), that design engineers adopt. This would help to ensure consistency between the NCC and current engineering standards.

The general engineering requirements that are typically applied in SA are:

a) All stormwater generated on-site during storm events up to and including a 100 year ARI must be effectively managed on-site and not enter any buildings, OR discharge onto adjacent land. This is known in engineering terms as managing the "major storm event"; and,

b) All stormwater generated on-site during storm events up to and including a 20 year ARI* must be captured and effectively managed on-site to prevent nuisance. This is known in engineering terms as managing the "minor storm event".

* AS/NZS 3500.3.2018 table 5.4.3 provides further guidance on selecting appropriate ARI's but it is generally recognized that the following ARI's are acceptable:
- 100 year ARI - box gutters / prevent entry to buildings or adjacent land
- 20 year ARI - roof gutters / downpipes
- 10 year ARI - on-site surface drainage systems
- 5 year ARI - street drainage systems