What Is NCZ 5 on a Boundary Fence? The 900mm Quadrant

Name: comparepoolquotes
Price range: $$$

NCZ 5 is the non-climbable zone on a boundary fence used as a pool barrier: a 900mm quadrant measured down from the top of the fence on the pool side. The fence must be at least 1800mm high inside. At 300mm below the top, the zone still reaches 849mm into the yard.

The short answer

NCZ 5 applies only to a boundary barrier, a fence between two properties, 1800mm or more high on the pool side. NCZ 1 to 4 apply to other barriers under 1800mm.
It is a quadrant, not a strip. Victoria’s practice note describes it as a quadrant created by a 900mm radius down from the top of the inside of the barrier, so it reaches into the pool area as well as down the fence.
Our clearance table: at 1500mm above the ground the zone extends 849mm from the fence; at 1200mm, 671mm; at 1000mm, 412mm; at 900mm it ends.
Queensland does it differently. The QBCC says a fence of at least 1800mm with an inside non-climbable zone is the option when you cannot make an outside one, with nothing at the bottom that reduces the inside height.
The fixes are cheap. The QBCC lists flat polycarbonate sheeting, vertical palings or a fillet at 60 degrees or more to make a climbable object non-climbable.

How far NCZ 5 reaches into the pool area at each height on an 1800mm boundary fence: our arithmetic on the 900mm quadrant measured down from the top inside edge, √(900² − depth below top²). Figure 2.2(a) of AS 1926.1-2012 is the authority
Height above inside ground level	Zone extends this far from the fence	What typically sits there
1,800mm above inside ground (0mm below the top)	900mm	Top of the fence: anything within 900mm, such as a pergola beam, shed roof edge or branch at fence height
1,500mm above inside ground (300mm below the top)	849mm	A pool-side rail near the top of a paling fence; a tree branch; a wall-mounted heater or meter box
1,350mm above inside ground (450mm below the top)	779mm	A trellis, a hanging planter, a hose reel on the fence
1,200mm above inside ground (600mm below the top)	671mm	A barbecue hood, a stacked chair, a tall pot plant
1,000mm above inside ground (800mm below the top)	412mm	The top of a 1,000mm-high object close to the fence
900mm above inside ground (900mm below the top)	0mm	Bottom of the zone: nothing below this height is inside NCZ 5

What is NCZ 5 on my boundary fence?

AS 1926.1-2012, the pool barrier standard, sets five non-climbable zones; how NCZ 1 to 4 work is on the pool fence non-climbable zone explained. Victoria’s building regulator summarises them in Practice Note SP 02: NCZ 1 to 4 apply to an internal barrier under 1800mm, and NCZ 5 ‘is only applicable to Boundary Barrier. It is a quadrant created by a 900mm radius down from the top of the inside of a boundary barrier.’

The same note sets the companion rule: a boundary fence ‘shall have a height of not less than 1800mm on the inside and NCZ 5 down from the top of the inside of the barrier, when it acts as a barrier to a pool’. Why the zone sits on your side, and the 50mm rail rule where an internal fence meets the boundary, are covered on whether your boundary fence can be the pool barrier. This page is about the shape of the zone, which is where boundary fences actually fail.

The word that matters is quadrant. A quadrant is a quarter-circle. Picture a 900mm radius swung from the top inside edge of the fence, from straight down to straight out into the yard. Everything inside that quarter-circle is NCZ 5. A NSW council handout puts the same idea in plain words: no potential handholds or footholds ‘within 900mm of the top of the pool fence in any direction’.

Inside the zone, Victoria’s practice note says, the standard requires that there be no plants that will facilitate climbing; a plant does not facilitate climbing if it does not act as a foothold or handhold, and judging that is left to the relevant building surveyor.

How far does NCZ 5 reach into the yard?

Because the zone is a quarter-circle, its reach into the yard shrinks as you go down. At the top of the fence it reaches 900mm out; at 900mm below the top it reaches nothing. In between, the distance is √(900² − depth²). The table above works it through for an 1800mm fence.

At 1500mm above the inside ground, 300mm below the top: 849mm.
At 1200mm, 600mm below the top: 671mm.
At 1000mm, 800mm below the top: 412mm.
At 900mm or lower: outside the zone.

This is our arithmetic on the geometry the practice note describes, not a figure the standard prints. The standard’s own diagram, Figure 2.2(a), is the authority, and a building surveyor or pool inspector makes the call on site. Use the table to find problems before they do.

The quotable version: NCZ 5 is a quarter-circle, so a shed roof 800mm from an 1800mm boundary pool fence at the fence’s full height is inside the zone, while a 900mm-high planter against the same fence is not.

Two consequences people miss. A taller fence moves the zone up, not down: on a 2100mm fence the zone is measured from the top, so it covers 1200mm to 2100mm. And the zone is on your side, so if a neighbour’s tree hangs over your fence inside the quadrant, the QBCC says you may need to negotiate with your neighbour to remove it.

What fails inside NCZ 5, and how to fix it

A boundary fence can fail on its own structure. A paling fence has horizontal rails, and if they face the pool, any rail more than 900mm above the ground on an 1800mm fence is inside the quadrant. The QBCC says rails are often a problem on timber paling fences where two fences join.

The QBCC’s fixes for a climbable object you cannot move:

flat polycarbonate sheeting or similar to shield the climbable object;
vertical palings over it;
a fillet with an angle of 60 degrees or more, so there is no flat surface to stand on.

Where rails on two fences meet at a corner, the QBCC says to fit a timber wedge to each rail for at least 900mm from the corner, inside and outside. If the rails are on your neighbour’s side, it says you might need to raise your fence to at least 1800mm and have no climbable objects within the upper 900mm on the inside.

Everything else is ordinary garden furniture. Walk the fence with a tape measure and check the table above: pergola beams, a shed roof edge, branches, trellis, hanging planters, a wall heater or a meter box on the fence, a barbecue hood, stacked chairs. Moving them costs nothing. If the fence itself is too low, the costs are on what it costs to raise a pool fence.

Is NCZ 5 the same in every state?

The geometry is the same wherever AS 1926.1-2012 applies, but the rules around it are not.

Victoria uses AS 1926.1-2012 and names the zone NCZ 5 in its practice note. The note adds that clause 2.3.1, the 500mm setback for steps and objects, does not apply to boundary barriers, citing a 2021 ruling on the standard; see the 500mm setback around a pool fence.
NSW: one council handout for pools built or installed after 1 May 2013 says fencing must comply with the Swimming Pools Act 1992 and AS 1926.1-2012, and a boundary fence that forms part of the pool fence must be at least 1800mm high measured from inside the pool area.
Western Australia: Building and Energy says pools and spas generally need barriers complying with AS 1926.1-2012, with pools installed before 1 May 2016 allowed to comply with the 1993 edition instead.
Queensland has one pool safety standard, MP 3.4, according to the Queensland Government, and a Queensland council lists AS 1926.1-2007 as the fencing standard it applies. The QBCC does not use the term NCZ 5. It presents the inside zone as an option: if you cannot make an outside non-climbable zone, you can build the fence at least 1800mm high with a 900mm zone on the inside, measured from the top, and the inside height must be 1800mm ‘with nothing at the bottom (such as a deck) that would reduce the height’.

So the honest answer to ‘what is NCZ 5’ depends on your state: a named zone with a fixed shape in Victoria and NSW, and an option rather than the rule in Queensland. State-by-state heights are on pool fence rules by state. If you are building and the boundary fence is part of the plan, ask each builder whether their barrier price includes bringing it up to standard, and compare pool quotes on that basis.

Common questions

What does NCZ 5 mean on a pool fence?

Non-climbable zone 5. Victoria’s Practice Note SP 02 says it applies only to a boundary barrier and is a quadrant created by a 900mm radius down from the top of the inside of the barrier.

How high does a boundary fence need to be for NCZ 5?

At least 1800mm on the inside, measured from the pool side. In Queensland the QBCC adds that nothing at the bottom, such as a deck, may reduce that inside height.

Can I have a garden bed against my boundary pool fence?

A low one sits below the zone: NCZ 5 ends 900mm below the top, so on an 1800mm fence anything under 900mm high is outside it. In Queensland the QBCC says nothing at the bottom, such as a deck, may reduce the 1800mm inside height, so check a raised bed with your inspector.

Does my neighbour have to move things away from our boundary pool fence?

No. Douglas Shire Council’s pool FAQ says it is the pool owner’s responsibility to make sure the fencing complies, and a neighbour does not need to move climbable objects on their land.

Are paling fence rails allowed inside NCZ 5?

Not if they can be climbed. The QBCC’s non-climbable zones guide suggests sheeting, vertical palings or a fillet at 60 degrees or more to make a climbable object non-climbable.

Sources

General information only, current at 2026-10-08. Pool rules differ by state and by council, and penalty amounts are updated regularly. Confirm your own obligations with your council or a registered inspector before acting.

What is NCZ 5 on a boundary fence?