Its important to consider ground movement when laying underground drainage as Master Plumbers technical expert, Sam Welsh explains.
In our regular Master Plumbers’ Series, our technical advice team shares the answers to some of the most asked questions. For our Winter Edition, Aaron Bridger takes on some of the questions that you have raised.
1 What are the restrictions placed on multi-layer piping; plastic-coated, semi-rigid, stainless-steel gas piping and their fittings?
These piping systems must terminate one meter away from the nearest part of any gas appliance. As outlined in AS/NZS 5601.1 clause 6.6.1, this distance is to prevent heat damage to the piping system caused by the appliance. This means you must connect to a metallic pipe one meter away from the appliance. Be mindful that brazing, welding, or annealing shall not be performed with less than one meter clearance from a joint containing non-metallic components as stated in Clause 5.2.12 of the Gas Standard. On the theme of joints, let’s cover some restrictions of mechanical joints:
• Where compression pipe fittings and flare fittings are being used you must ensure they are accessible, this is to allow for the nut to be tightened.
• Screwed pipe fittings shall only be used in accessible and ventilated locations, found in clause 5.1.7.
Note: Accessible is defined in AS/NZS 5601.1, as access can be gained without hazard or undue difficulty for inspection, repair, testing, renewal, or operational purposes.
2 Can you clarify HB39’s, clause 5.7.7, which pertains to downpipe spreaders?
This clause outlines that spreaders may be used to drain rainwater from a higher roof surface, with a catchment not exceeding 15m², providing that the conditions of the clause are satisfied. What’s catching practitioners out is the following requirement:
• (a) when discharging onto a tiled roof, the lower section is sarked a minimum width of 1800mm, either side of the point of discharge and extending down to the gutter. There is a lengthy list associated with this clause. If you do roofing work, please familiarise yourself with the requirement.
3 What is the minimum size of balcony and terrace drains, and do they fall under clause 6.3.3 of 3500.3 minimum diameter of stormwater drainage?
Balcony and terrace drain sizing don’t currently fall under this clause. The size of balcony drains needs to be calculated on the total hydraulic load, as above:
Clause 3.8. Balcony and terrace areas
Systems for draining balconies and terraces shall be designed for in Australia.
• 5% AEP (20 years ARI) rainfall intensity and,
• 1% AEP (100 years ARI) rainfall intensity for overflow
Any other approved outcome would be developed as a performance solution under the provisions of the NCC.