How Much Does a House Extension Cost in Queensland?

A house extension in Queensland is priced by the square metre of new floor area, and there is no single rate, because the rate changes depending on where you put that floor. A ground-floor addition on a level, well-drained block is the cheapest square metre you can add to a house. A second storey is the dearest, because you pay to investigate, strengthen and weatherproof a house that is already standing before you build anything new. A detached studio sits between the two: no structural surgery on the existing house, but its own footings, its own roof and a services run from the main building. Anyone quoting one state-wide dollar figure per square metre for “an extension” has not looked at your house. Here is what actually sets your rate, and the compliance triggers that apply on the Sunshine Coast and in Noosa Shire.

Ground floor vs second storey vs detached: what sets the rate per square metre

The useful comparison is not a headline number but what each square metre has to pay for before it becomes usable floor area. Two of the three formats make you buy things that never show up as living space. That is the whole story of extension pricing.

We do not publish a fixed dollar rate per square metre, and you should be wary of builders who do. The same 40m² addition differs enormously between a flat block at Cotton Tree and a stepped site at Ninderry, and a rate quoted before anyone has seen your footings, your roof structure or your flood mapping is a marketing number rather than a price. For how square-metre rates are built up generally, see our guide to renovation cost per square metre in Queensland.

Why a second storey costs more per square metre than the drawings suggest

Owners often assume a second storey must be cheaper, because there is no land to buy and no slab to pour. In practice, four costs land before the new floor exists.

• The existing house has to carry the load. Footings, stumps, bearers and wall frames designed for a single storey are now supporting another one. That means engineering, and often underpinning, new posts down to new pad footings, or steel where the old timber cannot do the job.
• The roof comes off. Removing and rebuilding a roof is a full trade sequence in itself, and while it is off the house below has to stay dry. Temporary weather protection is a real line item here, where a summer storm can undo a fortnight of work in an afternoon.
• You build floor area and then delete it. A staircase consumes floor on the lower level and creates a void on the upper level. You pay to frame, line and finish that area on both levels and gain living space from neither.
• Compliance follows the new work into the old house. Where new construction connects to existing rooms, smoke alarms, balustrades, stair geometry, waterproofing and energy provisions come into play. The Queensland Development Code carries Queensland-specific requirements alongside the National Construction Code, including MP 4.1 for sustainable buildings, and your certifier confirms what applies to your scope.

This is also why second-storey jobs are the most variation-prone extension type. Under the QBCC rules a variation must be presented to you in writing and agreed by you in writing before the varied work starts, and the contractor must give you a written copy before the earliest of the variation work starting or five business days from the day both parties agree. The variation must describe the work, give the date of the request, state any estimated delay, and set out the price change or how it will be calculated. Our guide to building contract variations in Queensland covers how to read one properly.

What a Sunshine Coast or Noosa site adds to the bill

The biggest reason two identical extension drawings produce different prices is the land underneath them.

Flood hazard

Sunshine Coast Council requires building work to be assessed against the flood hazard area and to comply with MP 3.5 Construction of Buildings in Flood Hazard Areas under the Building Regulation 2021. The council supplies flood information searches giving the defined flood level, maximum flow velocity, freeboard and finished floor level for a property, and notes that fees apply. On low-lying land near the Maroochy River or at Cotton Tree, a required floor level can decide whether a ground-floor addition works at all, or whether you are pushed into a suspended floor and a set of steps.

Wind and coastal exposure

Sites at Coolum Beach, Marcus Beach, Yaroomba and Noosa sit close enough to open water that wind classification and durability matter. Wind classification for housing is determined site by site under AS 4055 Wind loads for housing, and it drives tie-down, bracing and glazing specifications. Coastal exposure also drives fixing and finish selection, because corrosion is a cost you either buy at construction time or pay for later.

Slope, access and overlays

An extension at Ninderry or on a stepped Noosa Heads block brings retaining, drainage, temporary works and machine access into scope before the extension itself begins. Bushfire construction requirements now come through planning scheme overlay mapping and AS 3959 Construction of buildings in bushfire-prone areas rather than the Queensland Development Code, since the Queensland Government records that QDC MP 2.4 has been repealed. Vegetation, waterway and overland flow overlays under the Sunshine Coast Planning Scheme 2014 and The Noosa Plan 2020 can also constrain where new footings may sit.

Approvals: what happens before anyone lifts a hammer

With both councils, a private building certifier issues your building approval and carries out the inspections. Sunshine Coast Council states that a private building certifier can advise whether you need a development permit for building work, and that some minor building work may be accepted development or exempt. Noosa Shire Council states that most building work requires development approval, including renovations, alterations or additions, retaining walls, carports, sheds and swimming pools, and that private certifiers assess compliance with the Building Act and associated standards.

The trap is that a certifier cannot approve work conflicting with the local planning scheme or the Queensland Development Code. Noosa Shire Council is explicit that where the work needs a variation to the QDC or the planning scheme, the application must go to council first through a Request for Referral Agency Response before the certifier can grant approval. That step quietly adds weeks to a program, which is why setbacks and height are worth resolving at sketch stage rather than at approval stage. We cover the full sequence in our guide to building approvals on the Sunshine Coast and in Noosa.

The contract rules that keep an extension budget honest

• $3,300 is the line that matters. The QBCC requires a written contract for domestic building work priced over $3,300 including labour, materials and GST, and home warranty insurance must be taken out for residential construction work valued at more than $3,300 including materials, labour and GST. Almost every real extension clears this by a wide margin.
• Contract levels. The QBCC classes contracts priced at $3,301 to $19,999 for renovations, extensions and routine repairs on existing homes as Level 1, and contracts priced at $20,000 and over as Level 2.
• Before you sign. For work priced at $20,000 or more, the QBCC requires the contractor to give you a copy of the QBCC-approved consumer building guide before you sign. The QBCC also states that all contracts for building work valued at over $3,300 must include advice about your right to a cooling-off period, and that the maximum deposit a contractor is allowed to request is based on the value of the works.
• After you sign. The QBCC requires the contractor to give you a copy of the signed and dated contract within five business days of entering the contract, and the commencement notice within 10 business days of work starting on site.
• What the insurance buys you. Under the Queensland Home Warranty Scheme the work is covered for six years and six months from the earliest of the day the premium is paid, the day you agree to a contract, or the day work starts. For a structural defect you must claim within three months of first becoming aware of it. For a non-structural defect you must become aware within six months after the work is substantially complete and claim within seven months.

Those protections only exist if your builder is licensed, so check the licence number on the QBCC licensee register before you commit to anything, using the steps in our guide on how to check a QBCC licence. For context on volumes, the ABS reported the value of approvals for alterations and additions to residential buildings at $1,288 million seasonally adjusted in July 2026, down 3.9 per cent for the month, and $3,976.2 million of alterations and additions work done nationally in the March quarter 2026, a rise of 4.1 per cent. Queensland total dwelling approvals were 4,200 seasonally adjusted in July 2026, down 13.9 per cent.

How we price an extension at Roebuck Concepts

We price extensions from documented drawings, an engineered design and a site inspection, not from a rate card. We open up and inspect what we reasonably can before contract where access allows, identify the structural unknowns in writing, and set out clearly what is included and what is provisional, so the variations that do arise are genuine rather than gaps we left in the scope.

Tom Roebuck is the director and a licensed builder with more than 20 years in residential construction, holding QBCC company licence 15280811 and individual licence 15015060, and Roebuck Concepts is a member of Master Builders Queensland. The Grandview project at Coolum Beach won three Master Builders Queensland 2025 Sunshine Coast Housing & Construction Awards, presented on 15 August 2025 at The Events Centre in Caloundra: Home Renovation/Remodelling Project over $1 million, Best Residential Swimming Pool, and Best Use of Innovation. To see how a large addition was handled on a real coastal block, look at the Grandview Drive Extension at Coolum Beach, and read more about how we work on the home extensions Sunshine Coast page. We work across the Sunshine Coast and Noosa Shire from our office at Coolum Beach.