Water retention tank

Owner builder looking to subcontract out an upper level deck with awning build. I live in the Northern Beaches council area in Sydney. The upper deck will be 6m above the ground.

I need DA approval and intend to submit the application myself. I have structural engineering, elevation and site plans but need to get my head around stormwater issues.

I intend to cover the deck with 16x3m insulated panel roof (48 sqm) from the existing titled roof gable. The existing title roof gutter will become impossible to service because of the awning and solar panels so I am going to remove this section of roof gutter and flow 24sqm of titled roof onto the awning. At 72sqm do I need a water retention device?

Can I include this in the scope of the roofer or do I need stormwater plumbing?

You just need the gutter and downpipe sizes to be compliant with the NCC for the roof area harvested and have the downpipes connected to a LPOD.

You need to ask your council about any retention tank requirements.

The tank will need an overflow pipe connected to the stormwater if the tank would otherwise overtop if an overflow pipe was not connected