Building a Deck in NZ: How a Deck Is Built

Wondering how to build a deck properly? Most of what decides whether a deck lasts is the part nobody sees once the boards are down. This guide explains how a deck is built in New Zealand, so you know what you are paying for, what to ask a deck builder, and what to check in a quote. If you are planning to build it yourself, it covers the decisions you need to get right.

In NZ, most decks are designed to NZS 3604, the standard for light timber framing, which sets pile, bearer and joist sizes and spacings for a given span and height.

3. Bearers, bearer spacing and deck post spacing

Bearers are the heavy beams that sit on the piles. Bearer spacing on a deck and deck post spacing go together: bigger bearers can span further between piles. NZS 3604 span tables set the combinations. Piles commonly end up somewhere between about 1.2 and 1.8 metres apart, depending on bearer size and load.

4. Joists and deck joist spacing

Joists run across the bearers and carry the boards. Deck joist spacing depends on the board: around 450mm centres is common for 32mm pine boards, hardwood boards may need 450mm or closer, and composite often needs 400mm or less, set by the manufacturer. Too wide and the deck feels bouncy and boards sag.

Fixing to the house

If the deck attaches to the house, it is fixed to the house framing through a stringer, with spacers and flashings so water cannot track into the wall. A badly fixed stringer is one of the most common causes of rot in the house itself.

• Pile treatment (H4 or H5), and how deep and how far apart they are
• Bearer and joist sizes, and joist spacing that suits the boards you chose
• Timber treatment levels: H3.2 for framing and boards above ground
• Fixing type: stainless or hot-dip galvanised, or the composite system's clips
• How it fixes to the house, including flashings
• Whether a balustrade or building consent is needed, and who handles it
• Whether removing the old deck is included

Our quotes list the timber, sizes and what is included in writing. Read when a deck needs consent or check what a deck costs.