How to Read an Itemised Deck Quote (and Spot the One Cutting Corners)

When a homeowner gets 3 deck quotes for the same job and they range from $14,000 to $33,000, the instinct is to assume two of the builders are wrong. Usually none of them are. They have simply quoted 3 different decks, and the only way to see that is to read the quotes line by line.

A proper itemised deck quote has 5 line items: frame, decking boards, fixings, finish, and balustrades. Here is what each one should tell you, and the substitutions that quietly drop a quote by thousands without dropping the quality you can see.

Line 1: the frame

The frame is the bearers, joists, posts and footings - the part of the deck you never see and the part that decides whether it lasts. The quote should state the joist spacing. For a residential deck that is usually 360mm or 400mm. A quote at 450mm spacing is a cheaper frame: fewer joists, less timber, less labour. It also makes the finished deck feel bouncy underfoot and shortens its life.

The frame line should also account for footings sized to your soil. On reactive-clay ground in Salisbury or Playford, footings go 1.2 to 1.5 metres deep. A quote that prices shallow footings on reactive clay has just saved money you will pay back when the deck heaves. The frame is designed to AS 1684, the standard for residential timber framing.

Line 2: the decking boards

This line should name the species or product, not just say "decking". "Merbau" and "treated pine" are hundreds of dollars per square metre apart. "Composite" should name the brand and whether it is capped. A quote that just says "decking boards - supply and fix" is hiding the single biggest material variable.

It should also say whether the timber is seasoned or kiln-dried. Green hardwood is cheaper and it cups and splits within 2 summers in Adelaide's climate. That is the substitution that does the most damage and is the hardest to see in a finished-looking deck.

Line 3: the fixings

Screws, joist hangers, bolts and brackets. The quote should specify the grade. For a standard inland deck, hot-dip galvanised may be fine. For a coastal deck at Glenelg, Semaphore or anywhere near the gulf, the fixings need to be 316 marine-grade stainless or class 4 galvanised, or they corrode and the structural connections weaken.

A quote that prices galvanised screws for a coastal deck is cheaper today and a problem in 5 years. The fixings line is small money on the page and large consequence on the deck.

Line 4: the finish

Oil, stain, or - for composite - nothing. The quote should say which, and how many coats. Two thin coats of oil is the correct application; one coat is half the product and half the protection. For a new merbau deck the finish line should also allow for managing the tannin bleed before the first coat goes on.

Line 5: balustrades

If the deck is over 1 metre high it needs a balustrade, and it is a safety barrier, not a finish. The quote should price it by linear metre and by style. A balustrade priced as a vague allowance, or left off a deck that legally needs one, is a quote you cannot compare and a deck that fails inspection.

What this means when you compare 3 quotes

Lay the 3 quotes side by side and read line for line. If one is far cheaper, the saving is in one of these 5 lines - wider joist spacing, a cheaper or greener board, lighter fixings, a single finish coat, or a missing balustrade allowance. None of that shows in a photo of a finished deck.

This is exactly why comparing 3 itemised quotes on the same scope beats comparing 3 dollar figures. A single lump-sum quote tells you nothing. Five line items tell you everything. If a builder will not itemise, that is your answer.