Do I Need an Overflow in My Bathroom Basin or Vanity?

Overflow holes in basins, they’re small, a bit hidden, and often overlooked during a bathroom reno. But do you really need one in your vanity or basin? And is it something that’s required under Australian building codes?

Let’s clear up the confusion

What's a basin overflow?

A basin overflow is that small hole near the inner top edge of some bathroom sinks. It connects to the waste and helps prevent the basin from spilling over if it fills up too much — like when the tap’s left running or the drain is blocked.

It doesn’t drain water fast, but it does give you a bit of a buffer before water ends up on your vanity top or bathroom floor. Basically: a handy little backup.

Is an overflow required in bathroom basins in Australia?

Here’s where it gets interesting.

Under the National Construction Code (NCC), a basin overflow is not always mandatory, but there are some situations where you need to plan for overflow protection.

The rules say:

Bathrooms (especially in Class 2, 3 and 4 buildings like apartments and multi-dwelling homes) must include some form of overflow protection, either:

A floor waste in the bathroom, or
A built-in overflow in the basin or bath

So if your bathroom doesn’t have a floor waste, then yep, you’ll need a basin with an overflow hole to stay compliant.

Quick building code recap

Standalone Home

Basin Overflow Required? Not always.

You can skip it if a floor waste is present and compliant.

Apartment / Unit

Basin Overflow Required? Often required.

Overflow must be handled — either via floor waste or built-in

Bathroom without a floor waste

Basin Overflow Required? Yes.

Basin must include an overflow to avoid flooding risk.

Basin with no plug hole cover

Basin Overflow Required? Not a substitute.

Overflow must be built-in, not just “not sealable”.

Can I skip the overflow?

You can if your bathroom floor has proper drainage (i.e. a compliant floor waste), especially in freestanding homes. But in apartments, or in bathrooms without floor drains, skipping the overflow is usually a no-go.

Also worth noting: some designer or stone basins don’t include overflows, so make sure your space is properly waterproofed and that you're covered by a compliant drainage setup.

Shop bathroom basins at The Blue Space

Whether you’re after a sleek modern basin with an overflow or a minimalist stone look without one, we’ve got plenty of styles to choose from — and all the info you need to make sure it’s the right fit.

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Do I Need an Overflow in My Bathroom Basin or Vanity?