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It will require plumbers and builders to pay close attention to the design and installation for the branch drain connections for sanitary plumbing installations for two storey houses.
There is potential if you have not designed the sanitary drainage system with this change in mind, that the first-floor ceiling joists may not be deeper enough to accommodate the added grade of the pipe.
The revised edition of AS/NZS 3500.2 amends Clause 22.214.171.124, 126.96.36.199 and 188.8.131.52, Clause 184.108.40.206.1, 220.127.116.11.2 and 18.104.22.168.3. These clauses have been brought into place to add clarity around when to apply figure 4.9.1(a). It applies to the typical connection arrangements for graded branch drains entering the main drain.
The changes to AS/NZS 3500.2 relates to junction connections where the main drain and the branch drain are both DN100mm.
Under the new edition of the standard, which will be adopted alongside NCC 2022. It will require that the entry level of branch drain be elevated at an incline of no less than 15 degrees (a minimum grade of 1:3.732) above the horizontal.
This is to prevent back wash and strandings at the junctures and in the branch drain from upstream connection, which have been found to cause blockages.
The new requirements will apply to new connection/junctures where the main drain and the branch drain are both DN100.
This does not alter the requirements for a fixture connected to a graded discharge pipe (as per clause 22.214.171.124) or junctures installed at grade (as per clause 126.96.36.199) and the installations must follow each applicable requirement.
For installations where the main drains and branch drains are not DN100; the work is repair work; or where WC pans are not installed up stream, the requirements are only recommended. The standard still allows the branch drain to be connected on grade.
Requirements for an unequal junction (where the branch drain is smaller than the main drain) with a branch drain having a 10mm minimum invert level above the soffit of the main drain (in accordance with figure 4.9.1(b)) will still apply. However, they do not need a 15-degree inlet as per figure 4.9.1(a).
The change to entry level (grade) will cause an increase to the depth of main drain. This depth will be directly proportionate to the distance from the change in direction in 45-degree bends to the junction.
The below table shows how the distance from the change in direction at the 45-degrees to the point of junction will affect the increases depth of the main drain.
|Distance from the 45-degree (bend) to the juncture||Change in depth from the 45-degree (bend) to the main drain|
All measurements have been rounded up to the nearest whole millimetre.
When the plumber is setting out their work, they will have to be aware of the added grading/depth requirements to ensure it will not affect the design. Furthermore, they will need to ensure that these depths do not affect the angle of repose/angle of influence of the building or the adjoining properties structures.
If you have a main drain (DN100) within a ceiling space and there is a branch connection of DN100mm you will have to assess if the ceiling space will be deep enough to accommodate the added grade of the pipe.
In scenarios where ceiling space is limited you may wish to consider.
It is recommended that you make your plumber aware of the changes and discuss how these changes may affect your design. This will limit issues with plumbing inspections your build.
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