OSD [ Above ground or Under Ground ] : Cumberland Council NSW

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Feb 18, 2026
6:13 pm

Hi All

We have a 2000L rainwater tank planned, and currently the OSD Basin 1 is proposed to be above ground in the backyard with surrounding walls (NSW Cumberland council property).

I’m trying to understand the practical benefits of above-ground OSD vs underground OSD.

Also, if we proceed with the above-ground option now, would it restrict us in the future if we want to:

Build a granny flat
Install synthetic grass
Add a deck or paved entertaining area

Has anyone gone through this decision and can share pros/cons, especially around future flexibility and council approvals?

Can we combine RWT with OSD? Would that be a good option?

Appreciate any advice or experiences. Attached is plan.

Ashington Homes

16/06/2025

Stormwater drainage/ OSD/ pit pump/ absorption trench cost

Building A New House

Normally if they have the correct engineer you can go CDC. Do you mind me asking if you are using a project home builder as this could impact the process

l0nglive

13/12/2025

Exterior wall NSW, talk me out of bricks in NSW

Building A New House

Same, I worry that cladding/render will require some maintenance, and replacement eventually. Bricks will be the last standing component in a build.

philipjohn123

20/10/2025

Creative Granny flat design to goes above 60 sqm limit?

General Discussion

You could design a 60 m² granny flat with an attached covered patio or carport — those don’t count toward the floor area but still add a lot of usable space.