Two decks of the same area can differ enormously in price. A low level deck sitting 300mm off flat ground is a straightforward build. A deck two metres up on a sloping block, with a stair, balustrade and structural posts into rock, is a different job entirely.
Here is what a builder is actually pricing.
The main cost drivers
Height off the ground
This is the biggest one. Once a deck is above a certain height, you need balustrade, stairs, more substantial posts and bracing, and often a compliant fall protection design. Low decks avoid most of that.
Footings and ground conditions
Footing depth and type are set by the structure and the soil. Rock, fill, reactive clay and slope all change the design. Digging into sandstone is slower and more expensive than digging into sand.
Substructure
Bearer and joist sizes follow spans, loads and the decking you choose. Wider joist spacing is not a saving if the material requires closer support.
Decking material
Hardwood, treated pine and composite sit at different price points, and so do the fixings. Hidden fixing systems cost more to install than top fixing. See timber versus composite decking for the practical comparison and the best timber for a deck in Sydney for species.
Stairs and balustrade
Stairs are labour intensive. Balustrade cost varies widely between timber, powder coated aluminium, wire and glass, and glass is a substantially different number to timber.
Access
If materials have to be carried through a house or over a fence, that is labour. Side access for a trailer and a wheelbarrow makes a real difference.
Extras
Screening, privacy panels, integrated seating, lighting, roofing over part of the deck, and connection to an existing structure all add cost.
Where the budget goes
| Element | What it involves | Cost sensitivity |
|---|---|---|
| Site preparation | Clearing, levelling, removing an old deck or paving | Moderate, high if demolition is involved |
| Footings | Excavation, concrete, post supports, engineering where required | High on rock or slope |
| Substructure | Posts, bearers, joists, bracing, hardware | Moderate and driven by spans |
| Decking | Boards and fixings | High, and entirely material driven |
| Stairs and balustrade | Stringers, treads, posts, infill | High once height triggers balustrade |
| Finishing | Oiling or coating, trims, fascias, screening | Moderate |
What separates a cheap deck from a good one
Most of the cost difference that matters is invisible once the boards are down:
- Correctly sized and spaced joists, so the deck does not bounce
- Hot dip galvanised or stainless hardware appropriate to the location, particularly near the coast
- Proper flashing and clearance where the deck meets the house
- Ventilation and drainage under the deck so timber dries out
- Correct fixing pattern and end sealing on hardwood
A deck that fails early almost always fails in the substructure, the fixings or the detail at the house wall, not in the boards.
How to compare deck quotes
Ask every builder to state:
- Decking species or product, board width and fixing method
- Joist and bearer sizes and spacing
- Footing type and whether rock excavation is allowed for
- Balustrade type and compliance approach
- Whether stairs are included, and how many treads
- Whether an existing deck or paving needs removing, and who disposes of it
- Whether coating or oiling is included
- Whether any approval is required and who obtains it
Ways to keep the cost sensible
- Keep the deck at a height that avoids balustrade if the ground allows it.
- Choose one good material rather than an expensive board with cheap hardware.
- Simplify the shape. Angles and curves cost labour.
- Do the substructure properly and reduce spend on decorative extras.
- If you want a roof over part of it later, set the structure up for it now. See how much a pergola costs in Sydney.
Does it pay off?
Well built outdoor living space is one of the more visible improvements you can make to a Sydney home. We look at that properly in does a new deck add value to your home.
ORT Constructions builds decks, pergolas and outdoor living areas as part of our decks and pergolas service, with our own carpenters doing the framing and finishing. If a deck adjoins a slab or paving, our concreting team handles that in the same program.
Frequently asked questions
- What is the biggest cost factor in building a deck?
- Height off the ground. Once a deck is high enough to require balustrade, stairs and taller structural posts, the cost per square metre rises well above that of a low level deck.
- Is composite decking more expensive than timber?
- Composite boards usually cost more upfront than treated pine and often more than hardwood, but they need less ongoing coating. The substructure cost is similar either way.
- Do I need approval to build a deck in NSW?
- It depends on height, size, position and your property. Some low level decks fall within exempt development limits, while larger or higher decks need approval. Confirm with your council or a certifier.
