Deck Builder Calculator

Building a deck in New Zealand costs vary widely depending on size, materials, and complexity. For a professionally installed deck using treated pine, expect to pay $400-800 per square metre; composite decking runs $800-1,500/m2 installed due to higher material costs. If you are a competent DIYer, materials-only costs for treated pine start from around $150-300/m2. A typical 20m2 deck therefore ranges from $3,000 (DIY pine materials) up to $30,000 (large composite, professional install). Key cost drivers include deck height (ground-level decks are cheaper), number of posts and stairs, balustrade requirements, and access difficulty. Always obtain at least three quotes from Licensed Building Practitioners. Source: BRANZ branz.nz; Building Performance buildingperformance.govt.nz.

In New Zealand, whether you need building consent for a deck depends on its height and attachment. Under the Building Act 2004 Schedule 1 exemptions, decks that are no more than 1.5 metres above the ground and are not attached to a habitable building more than 1.5 metres above ground can generally be built without consent. However, any deck exceeding 1.5m in height, or one attached to a building at that height, requires a building consent from your local council. Regardless of consent requirements, all deck construction must still comply with the New Zealand Building Code. Always check with your local council before starting work, as territorial authorities may have specific local rules. Source: Building Act 2004 (NZ); Building Performance buildingperformance.govt.nz.

The best decking timber for New Zealand conditions depends on the application and your budget. H3.2 treated pine is the most common choice for above-ground decking: it is affordable, widely available, and resistant to rot and insects when properly maintained. H4 treated timber is required for any timber in ground contact (posts, bearers). Cedar is naturally durable and attractive but costs more. Composite decking (wood-plastic blend) offers low maintenance and is resistant to splintering, fading, and moisture, making it ideal for the NZ climate. Hardwoods such as kwila (merbau) are popular for their durability and appearance, but there are sustainability and sourcing concerns. All decking timber should comply with NZS 3602. Source: BRANZ branz.nz; Building Performance buildingperformance.govt.nz.

To calculate decking board quantities, first determine your deck area in square metres (length multiplied by width). Divide the total area by the coverage per lineal metre of your chosen board width (accounting for spacing gaps). Add 10-15% for waste from cuts and misaligned boards. For a standard 90mm wide board with a 5mm gap, each lineal metre covers approximately 0.095m2. For example, a 20m2 deck needs roughly 211 lineal metres of decking boards plus waste. Also calculate framing: joists typically at 450mm centres, bearers at 1.2-1.8m centres, posts and concrete footings. Include fixings (screws or hidden clips), joist hangers, post anchors, and any balustrade materials in your estimate. Source: BRANZ branz.nz; Building Performance buildingperformance.govt.nz.