Height above ground decides most of what a deck actually costs.
When people budget for a deck, they often start with decking material — timber against composite — because that is the visible, tangible choice. But the substructure underneath the visible surface, and whether a balustrade is required around the edge, are usually the bigger cost factors, and both are set almost entirely by how high the deck sits above finished ground level at its tallest point. A deck close to the ground needs a simpler substructure and generally does not trigger a balustrade requirement. A deck a metre or more above ground needs engineered footings suited to the span and height, and in most cases a compliant balustrade around any edge with a fall over the general one-metre threshold.
This page sets out cost bands by height above ground, the specific factors that move price within a band, and how decking material fits in once the substructure and balustrade question is resolved. If the site has enough of a level change that a deck is being compared against a patio, the decks and patios comparison in the services section covers that decision in more depth.
Cost drivers
What moves the price within a height band.
Substructure and balustrade requirements, both set by height, explain most of the price spread between decks of a similar footprint.
Planning noteTwo decks of the same footprint can differ enormously in price purely because of height — always compare quotes at a stated height above ground, not just floor area.
Compare decking materials
Timber and composite decking, once the substructure is settled.
Material choice affects appearance, maintenance and material cost, but does not change the substructure or balustrade requirements set by height.
Standard timber decking
Material costGenerally the lowest of common options
MaintenancePeriodic oiling or staining required to maintain appearance
Best fitMost residential decks where ongoing maintenance is acceptable
Composite decking
Material costHigher than standard timber, often meaningfully so
MaintenanceMinimal — no oiling or staining required
Best fitWhere low maintenance matters more than upfront material cost
Feature hardwood decking
Material costHigher again, dependent on species
MaintenancePeriodic maintenance, similar to standard timber
Best fitWhere appearance and durability both matter and budget allows
Worked scenarios
Two decks of similar footprint, different heights.
Both scenarios cover roughly 24m² of decking, but height above ground moves the price substantially.
24m² deck, 350mm above ground, off a slab home
A low deck stepping down from a ground-floor living area, with no balustrade required at this height and a straightforward substructure on shallow footings. Standard timber decking is specified. This scenario sits in the Entry band, typically $12,000–$16,000, with the substructure and footings being a comparatively small share of the total given the low height.
24m² deck, 1.1m above ground, off a raised living area on a sloping site
The same footprint but stepping down from a raised living area on a sloping section, requiring engineered footings suited to the height and a compliant balustrade around three exposed edges. This scenario moves into the Typical to Complex range, commonly $28,000–$38,000, with the balustrade and engineered substructure together accounting for a substantial share of the increase over the low-deck scenario.
Before comparing quotes
Confirm scope is genuinely comparable.
Deck quotes are easy to compare incorrectly if height and balustrade inclusion are not stated explicitly.
- Confirm the height above ground at the deck's tallest point, not an average or the height at the house line only.
- Ask whether a balustrade is required at that height and whether it is included in the quote, and to what style.
- Check what footing depth and post spacing the substructure is specified to, particularly on sloping or soft ground.
- Confirm the decking material's expected lifespan and maintenance schedule against your own upkeep expectations.
- Ask how the new deck sheds water away from the house and whether any flashing detail at the house junction is included.
Frequently asked questions.
At what height does a deck need a balustrade in New Zealand?
The Building Code generally requires a barrier wherever a fall of more than 1 metre exists, though the exact application depends on the specific edge and site — this should be confirmed against the current Building Code and with a licensed building practitioner for the deck in question.
Why is a taller deck disproportionately more expensive than a low one of the same size?
Because footing depth, post size and balustrade requirements all scale with height, and a taller deck crosses the fall threshold that triggers balustrade cost — the visible decking area stays the same, but the substructure and safety barrier underneath and around it both cost more.
Is composite decking worth the extra cost over timber?
It depends on how much ongoing maintenance you are willing to do. Composite carries a higher material cost but avoids the periodic oiling or staining that timber decking needs to maintain its appearance over time.
Does a deck attached to the house cost more than a freestanding one?
Attachment itself is a relatively small cost factor compared with height and span — a freestanding deck of the same height and footprint typically needs a similar substructure, though attachment does require correct flashing and weathertightness detailing at the house junction.
Sources & methodology
Designed to show its working.
Deck height, balustrade and consent requirements vary by council and site. This page sets out general planning ranges; structural and consent requirements should be confirmed for the specific property with a licensed building practitioner.