Deck balustrade rules and heights (the NCC)

A balustrade is the one part of a deck with a rule behind it. Get it wrong and it fails the inspection, or it gets pulled up later. It is also the part a lump-sum quote loves to leave vague. Here is the plain version of what the standard asks for.

The short answer

Under the NCC, once a deck is more than one metre above the ground it needs a compliant balustrade. The rule is plain. The rail must be at least one metre high. The gaps must stay under 125 mm, so a child cannot fit through. And there must be a non-climbable zone, so a child cannot use a foothold to climb up. Below a metre you usually do not need one. Many owners still want a rail or an edge.

The rules that catch people out

• The trigger height. One metre of drop is the line. Measure from the deck surface to the ground below, and remember a sloping yard can put one end over the line while the other is under it.
• The gaps. Under 125 mm everywhere, including below the bottom rail and between balusters or glass panels.
• The climb zone. No horizontal rails or footholds on the climbable face that a child can use as a ladder.
• Higher decks, stricter again. The higher the deck, the more the standard asks of the rail and the loads it has to take, which is why a high deck is engineered, not guessed.

Timber, metal or glass

All three comply when they are built right. So the choice is about look, budget and the view. Timber is the lowest cost and the warmest look. Metal is usually powder-coated aluminium or steel. It sits in the middle on price and stands up well to the coast. Frameless glass is the dearest. It keeps the view wide open, which is why it suits a deck that looks out to the water. We size the panels and the gaps so the one you choose passes.

A balustrade that looks fine can still fail on a single wide gap or a climbable rail. We build to the standard from the start, and name the spec on the quote, so the inspection is a formality.

Why it goes on the quote

A balustrade named to the NCC on the quote is one you can trust. It states the height, the gap and the material. So there is nothing vague to argue about, and nothing for an inspector to pull up. A quote that just says "we will sort a rail" has no spec and no standard. That is the one that gets knocked back on a gap. Then it costs you again to fix.

How we build balustrades at Deckline

We build every balustrade and elevated deck to the NCC, in timber, metal or glass. We name the spec on the quote, so it passes rather than gets pulled up. On a high deck we engineer the footings and posts for the height too. The rail is only as good as the substructure under it. This is general guidance, not a substitute for the certifier's sign-off.