In this guide
You've described the same deck to two builders. Same rough size, same material, same location. Then the quotes arrive — and they're thousands of dollars apart.
It's one of the most common points of confusion for Melbourne homeowners thinking about composite decking, and it's rarely a case of one builder being dishonest and another being straight. More often, the quotes are simply not describing the same thing — and it takes some unpacking to see where the differences actually lie.
This guide walks through every factor that legitimately drives variation in composite deck pricing. Understand these, and you'll be equipped to compare quotes accurately — and ask the right questions before you commit.
Why the Same Job Can Produce Very Different Numbers
Composite decking projects look deceptively straightforward on paper. A deck is a deck. But behind any finished surface sits a series of decisions — material grades, substructure specifications, layout choices, included scope — and each one has a cost attached to it.
Two quotes can describe a 5×4m deck and mean completely different things in terms of what gets built, what gets included, and what standard it's built to. The price gap almost always reflects those differences, not a discrepancy in profit margins.
The honest truth about cheap quotes
A significantly lower quote isn't necessarily better value — it often means a lighter substructure specification, a lower-grade board product, or a scope that excludes items you'll need to add later. Before treating the lowest number as the benchmark, establish what it actually includes.
The Substructure: Where the Real Differences Hide
The boards you walk on are the visible part of a composite deck. The substructure beneath them — the framework that carries everything — is where most of the engineering, material cost and labour investment actually lives. And it's where quotes diverge most significantly.
Joist material
Subframes can be built from treated pine, steel, or composite joists. Each has a different price point, a different expected lifespan, and a different susceptibility to moisture and movement. A steel subframe costs more upfront but typically outlasts a timber frame by decades and doesn't move, warp, or attract borers. What material is specified in the quote matters — a lot.
Joist spacing
Industry standards for composite decking typically call for joists at 300–400mm centres. Some builders quote wider spacing to reduce material costs. The result isn't visible once the boards are down — but it affects how the deck feels underfoot, how it performs over time, and whether the board manufacturer's warranty remains valid. Always ask what joist spacing is being specified.
Bearer and post sizing
For elevated or freestanding decks, the specification of bearers and posts determines how the structure handles load distribution over time. Under-specifying here is another place where a quote can look competitive while delivering a structurally lighter result.
The substructure question to ask every builder
Ask each builder to specify: joist material, joist spacing, bearer sizing, and post specification. These four details alone will explain a significant portion of any pricing difference between quotes.
Board Brand and Grade
Not all composite decking is the same material. The category includes a wide range of products — from entry-level boards with a relatively short warranty and limited colour range, through to premium capped composite products with 25-year warranties, high-definition wood grain patterns, and substantially better UV, moisture and stain resistance.
A quote specifying a premium product like Trex Transcend or Millboard will cost more than one built around a generic composite board. But the boards behave differently over ten years — in fade, in moisture management, in how they feel and look. A price difference here is a product difference, not a margin difference.
Ask each builder to specify the exact board brand, product range and colour. If they're not willing to name the product, that's a useful signal in itself.
Deck Features and Finishes
How a deck is laid, and what finishes are applied around its perimeter, has a direct bearing on both cost and the quality of the finished result.
Board layout
A standard linear lay — boards running parallel, typically in the same direction — is the most efficient pattern to install and generates the least waste. It's the baseline for most quotes.
A herringbone picture frame layout is a different proposition entirely. The picture frame — a border of boards running perpendicular to the field — requires precise mitred corners and careful planning to execute cleanly. Herringbone within that frame takes precision cutting and significantly more time to lay. The waste factor rises considerably. Done properly, the result is noticeably more distinctive and crafted-looking. Done quickly or without the right experience, the joins show. It's work that adds real impact to the finished deck — and that impact is reflected in the cost.
Fascia boards
Fascia boards conceal the perimeter of the subframe, giving the deck a clean, finished edge rather than exposing the structural framework. Some quotes include them; many don't. It's worth checking explicitly.
Composite edging
Composite edging strips cap the exposed ends of cut boards around the perimeter. Without them, board ends are visible — not a failure, but not the most refined finish. Ask whether edging is included or quoted separately.
Steps and balustrades
For elevated decks or those requiring a change in level, steps and balustrades are often treated as a separate scope — meaning they may not be in the base quote at all. Balustrade specification (glass, aluminium, timber post) also varies significantly in cost. If your deck needs either, confirm they're accounted for before comparing totals.
Site Conditions and Access
Two decks of identical size can cost meaningfully different amounts to build depending on what the site demands.
Ground conditions affect footing depth and type. Hard rock close to the surface creates drilling challenges. Soft or fill ground may require deeper footings or a different footing approach. This isn't something that can be fully assessed without visiting the site — which is one reason why any quote produced without a site visit should be treated with caution.
Height above ground changes the structural requirements and the labour involved. A ground-level platform is structurally simpler than an elevated deck with significant post height. Labour time and material specification both increase with height.
Access affects how quickly and efficiently materials can be moved in. Tight side access, steep blocks, or limited vehicle access all add time to the job — and time is a real cost that honest quotes reflect and less careful quotes ignore.
Demolition and removal of an existing structure is another variable. If there's an old deck or paving to remove first, that work takes time and typically involves skip bin hire or equivalent disposal. It may appear in a quote as a line item or not appear at all.
Not sure what your quote should include?
We visit every site before quoting — and we'll walk you through exactly what we've specified and why.
What's Often Left Out of Quotes — Ask Every Time
Before comparing any two quotes side by side, confirm whether each of the following is explicitly included or excluded. A quote that omits several of these can appear thousands of dollars cheaper while actually representing a larger total spend once the missing items are added.
Items to confirm are included in every quote
Ask whether these are included before comparing any quotes- Demolition and removal of existing deck or structure If you have an existing deck, paving or structure to remove, confirm this is scoped and priced — it's often quoted separately or omitted entirely.
- Fascia boards Concealing the subframe perimeter with matching fascia gives the deck a finished, professional edge. Not always included by default.
- Composite edging Capping exposed board ends cleanly around the perimeter. A small detail that makes a visible difference to the finished result.
- Steps and balustrades Often priced as a separate scope entirely. If your deck requires either, ensure they're included — and if balustrades are quoted, confirm the specification (glass, aluminium, powder-coated).
- Deck lighting Rough-in wiring for immediate or future deck lighting. Significantly easier and cheaper to install during the build than retrofitting later.
How to Compare Quotes Fairly
Once you've gathered quotes, the goal is to get them onto a level playing field before making a decision. A few steps make this significantly easier:
Request line-item breakdowns. A single lump sum tells you almost nothing. Ask for the quote to be broken into: substructure materials, board supply, labour, and any additional scope items. This is the only way to identify where differences actually sit.
Confirm the board specification in writing. Brand, product name, colour and warranty length. These should be explicit, not generic references to "quality composite decking."
Check the substructure specification. Joist material, joist spacing, bearer sizing. If a builder can't or won't specify these clearly, the ambiguity is itself a risk.
Ensure every quote covers the same scope. Use the checklist above. If one quote includes demolition and fascia boards and another doesn't, add those costs before comparing totals.
Ask about the warranty — on both product and workmanship. A composite board with a 25-year product warranty means nothing if the installation warranty is 12 months. Both matter.
A useful question to ask every builder
"If I came back in five years unhappy with how this deck has performed, what would you point to as the reason — and what have you done in this build to prevent that?" The answer tells you a great deal about how carefully the builder has thought through the specification.
Our approach to quoting
We visit every site before producing a quote. It's the only way to give you a number that's accurate — one that accounts for your specific ground conditions, access, existing structures, and the finishes that will make the space work properly.
Every quote we produce specifies the board brand and range, the full substructure specification, and a clear list of what's included and what isn't. We don't work from templates applied to photos. We work from what we've actually seen.
If you've already got a quote you'd like us to review, or you're starting from scratch, we're happy to walk you through the process — no obligation, no pressure.