Brisbane offers an extension option that no other Australian city has at scale: instead of building outward and losing the yard, or upward at great expense, you can lift the existing house and build a new level underneath it. On a raised timber home — which describes a very large share of Brisbane’s inner and middle ring — this frequently doubles the house on the same footprint.
That does not make conventional extensions irrelevant. But it does mean any Brisbane extension decision should start by asking whether building under is possible, because when it is, it is often the better answer.
What Extensions Cost in Brisbane
Brisbane new construction and extension work runs $2,500 to $4,500 per square metre. Building in underneath a raised house runs higher, at $5,000 to $6,500 per square metre, because you are working beneath an existing structure with restricted access.
Conventional extensions
- Small rear addition, 20 to 30 sqm — $65,000 to $135,000
- Medium ground-floor addition, 30 to 50 sqm — $120,000 to $225,000
- Large ground-floor addition, 50 to 70 sqm — $180,000 to $320,000
- Rear open-plan addition with new kitchen — $140,000 to $290,000
- Second-storey addition on a lowset brick home — $260,000 to $520,000
Raise and build under
- Raising the house — from around $100,000, varying with size, access, soil conditions and lift height
- New lower level — $5,000 to $6,500 per square metre
- Internal staircase — $8,000 to $25,000
- Reconnecting services — $15,000 to $40,000
- Typical project adding 100 sqm — $450,000 to $750,000 all in
Inside those numbers
- Demolition and site preparation — $5,000 to $18,000
- Excavation and footings — $15,000 to $50,000, higher on Brisbane’s sloping sites
- Slab or subfloor framing — $14,000 to $38,000
- Structural frame and roof — $28,000 to $85,000
- Removing a load-bearing wall with a steel beam — $6,500 to $13,000
- Windows and external doors — $12,000 to $45,000
- External cladding — $150 to $400 per square metre
- Roofing — $90 to $180 per square metre
- Services rough-in and fit-off — $15,000 to $40,000
- Internal linings, painting and joinery — $26,000 to $72,000
- New kitchen within the addition — $28,000 to $58,000
- Termite management system — $2,000 to $6,000, and mandatory
- Landscaping and making good — $9,000 to $40,000
Before construction
- Building design or architectural documentation — $5,000 to $40,000
- Structural engineering — $2,500 to $6,000
- Soil classification — $600 to $1,500
- Survey — $1,200 to $3,000
- Energy compliance assessment — $400 to $1,200
- Private certifier building approval — $2,000 to $6,000
- Development application where an overlay applies — $1,500 to $6,000 in fees plus consultants
- Character or heritage report — $2,000 to $6,000
Allow $12,000 to $45,000 in pre-construction costs on a Brisbane extension, more where the character overlay applies.
Build Under: The Feasibility Test
Before costing anything else, two height numbers determine whether building under is possible:
- 2.4 metres minimum ceiling height for a habitable room under the National Construction Code. Below that, the space can only be garage, laundry or storage.
- 9.5 metres and two storeys is the typical Brisbane City Plan height limit for houses. Other South East Queensland councils range from roughly 8 to 10 metres.
Between those two sits your envelope. A house already sitting high may have no headroom to be raised further; a very low-set house may need a substantial lift. Any competent Brisbane building designer can assess this in an hour, and it should be the first question asked.
Where the character overlay applies, raising a pre-1947 dwelling above specified heights triggers a development application — so the planning question and the height question have to be answered together. See our guide to renovating a Queenslander.
Approvals
Brisbane extensions need a building approval from a private certifier in essentially every case. Whether they also need a development approval from Brisbane City Council depends on the overlays.
The triggers that matter most:
- Traditional Building Character Overlay. Demolition of a pre-1947 dwelling or a substantial part of it, raising above specified heights, front extensions, and street-visible facade or roof changes all trigger an application. Rear alterations not visible from the street typically remain accepted development.
- Flood overlay. Minimum habitable floor levels and flood-resilient materials apply. Get a FloodWise Property Report first.
- Landslide hazard overlay on Brisbane’s steep inner-western and hilly suburbs, requiring geotechnical input.
- Bushfire, biodiversity and waterway corridor overlays.
- Designs that breach the applicable code on setbacks, site coverage, height or privacy.
A single-storey rear extension on a post-1947 home with no overlays, designed within the code, frequently needs no development application at all — two to four weeks for a building approval rather than four to nine months. That is the single biggest lever on your programme. Check the overlays through Brisbane City Council’s online planning tools before you design. Our guide to Brisbane approvals covers both pathways.
Extension Types That Work in Brisbane
The rear deck and open-plan addition
The most common and often the most effective Brisbane move: open the rear of the house into a single kitchen, dining and living space, and connect it through wide doors to a large covered deck.
What determines success here:
- Orientation for breeze, not sun. Brisbane’s summer relief comes from the north-easterly. An addition that preserves the cross-ventilation path is comfortable without air conditioning for much of the year; one that blocks it is not.
- Shade before glazing. Deep eaves, a verandah or a roofed deck stop heat before it reaches the glass. This is cheaper and more effective than high-performance windows in this climate.
- Level continuity to the deck. A near-flush threshold with a drainage grate makes the outdoor space part of the house.
- Ceiling height and fans. Raised ceilings let hot air stratify; fans in every space.
- Roof colour and sarking. Light roof, reflective sarking, ventilated roof space.
Building under
Discussed above. On a raised Queenslander this preserves the yard entirely, uses the existing roof and footprint, and delivers the largest area gain per dollar available in Brisbane. The constraints are the two height rules and the character overlay.
The second storey on a lowset brick home
Common in Brisbane’s post-war middle ring. More expensive per square metre than building under, because the roof must come off, the existing walls and footings must be assessed for the additional load, and the household usually cannot remain in occupation. Budget $260,000 to $520,000 and get an engineer’s assessment of the existing structure before commissioning any design.
The side extension
Where the block is wider than the house — common in middle-ring Brisbane — extending sideways adds width to narrow rooms. The constraints are side setbacks under the applicable code and, on a timber house, the need to maintain the termite inspection zone at the base of the new wall.
The covered outdoor room
The cheapest usable space in Brisbane. A roofed alfresco area costs $25,000 to $75,000 against $2,500 to $4,500 per square metre for enclosed space, and in this climate it is used year-round. See our guide to Brisbane decks and alfresco areas.
The Structural Realities
Termites and the junction
Where a new extension meets an existing timber house, the termite management system must be continuous and the inspection zone must be maintained. A new slab abutting an old stumped house, built up to the wall line, can create a concealed entry path. This must be designed, not improvised on site.
Steep sites
Brisbane is hilly, and much of the inner west, Kangaroo Point and the northern suburbs sit on genuine slopes. Consequences: engineered footings and often piers, retaining walls, restricted machine access, craneage, and where a landslide hazard overlay applies, geotechnical investigation. A sloping site can add 15 to 30 per cent to an extension.
Joining new to old
A new slab-on-ground addition attached rigidly to an existing stumped timber house will move differently. Articulation joints or matched foundation systems are required. Where the existing house needs restumping, do that first — do not attach a new building to a moving one.
Stormwater
An extension increases roof and impervious area, which must be collected and directed to a lawful point of discharge. Given Brisbane’s rainfall intensity, size this generously.
Energy Compliance in a Cooling Climate
Queensland applies the National Construction Code energy provisions through the Queensland Development Code, with requirements generally applying to the new work on a renovation.
The practical difference from southern states: in Brisbane’s climate, the assessment rewards shading, ventilation, roof insulation, reflective sarking and light roof colours far more than glazing performance and airtightness. Designing for breeze and shade is both the cheaper and the more effective compliance path — which conveniently aligns with what makes a Brisbane house pleasant to live in. Budget $400 to $1,200 for the assessment.
Timelines
- Design and documentation — 8 to 20 weeks
- Development approval, where required — 8 to 36 weeks
- Building approval — 2 to 4 weeks after complete documentation
- Tender and contract — 4 to 8 weeks
- Construction, single-storey addition — 14 to 26 weeks
- Construction, raise and build under — 24 to 40 weeks
- Construction, second storey — 24 to 40 weeks
End to end: six to twelve months for a straightforward extension with no development application, twelve to twenty-two months where one is required, and fourteen to twenty-six months for a raise and build under in a character area.
Brisbane’s storm season adds a constraint. Work involving an open roof or exposed structure between November and March carries genuine weather risk, and builders programme around it. A raise-and-build-under project should aim to have the house re-supported and weathertight before the wet season.
Licensing and Warranty
Queensland’s thresholds are low and they apply to every extension:
- A QBCC licence is required for building work over $3,300, and at any value for plumbing, drainage, gas fitting, termite chemical treatment, building design and site classification
- Queensland Home Warranty Scheme cover is compulsory above $3,300, paid by the contractor to the QBCC and passed through in the contract
- Cover runs 6 years and 6 months from the earliest of contract, premium payment or commencement, with a $200,000 maximum
- Using an unlicensed contractor may void that cover entirely
Verify the licence on the QBCC register before paying a deposit. See our guide to vetting a Brisbane builder.
Getting It Right
- Check the overlays and flood status before design. This determines your timeline more than anything else.
- Test build-under feasibility first if the house is raised. It may be the better project.
- Get the soil classification and, on a slope, geotechnical advice before designing footings.
- Have an engineer assess the existing structure before contemplating a second storey or a lift.
- Design for breeze and shade, not for solar gain.
- Detail the termite management at the junction between new and old, explicitly.
- Document thoroughly. Cheap drawings produce expensive variations.
- Hold 15 to 20 per cent contingency. Extensions expose the existing house, and in Brisbane that means termites and rot.
The Brisbane extensions people are happiest with years later share a pattern. They kept the breeze path open, they put a roof over the outdoor space, they got the termite detailing right at the junction, and — where the house allowed it — they went down rather than out, and kept the yard.
Living Through an Extension in Brisbane
Whether you can stay depends on the work and the season.
- A rear extension is usually survivable if the existing kitchen and a bathroom remain functional and temporary weatherproofing separates the works.
- A raise and build under is not. The house is jacked and held on temporary supports; you must move out for that phase at minimum, and usually for longer.
- A second storey generally is not, because the roof comes off.
- Any extension involving the only bathroom requires a temporary arrangement or relocation.
Brisbane-specific practicalities:
- The wet season is the constraint, not the cold. A house with an open wall in February faces storm rain and high humidity, and dust migration is worse when the air conditioning cannot run.
- Build the deck early if you can. A covered outdoor area completed at the start of a project becomes a genuinely usable temporary living and dining space in this climate — a sequencing advantage unique to Brisbane.
- Termite treatment may require temporary vacating depending on the method used.
- Storage — $200 to $450 per month for a typical household.
- Temporary accommodation — $2,200 to $5,500 per month for a Brisbane family home.
Getting the Design Brief Right
The extensions that disappoint are the ones where the brief was expressed as area rather than function. Before engaging a designer, write down:
- What specifically does not work in the current house, room by room
- How the household actually uses the space, and where they spend summer evenings
- Where the breeze comes from and what currently blocks it
- Which outdoor space matters and how the house should connect to it
- What storage is missing
- The budget, honestly, including consultants, approvals and contingency
- Whether build-under is an option, and whether this extension would foreclose it
That last point matters in Brisbane and nowhere else. A ground-level rear extension built against a raised house can make a future build-under project substantially harder or impossible. If the house could be lifted, resolve that question before adding anything at ground level.
The Question to Ask Every Builder
Before signing anything, ask each builder how they will maintain the termite management system and the inspection zone at the junction between the new extension and the existing house.
A builder who works properly in Brisbane will describe a continuous barrier, a maintained inspection gap, and materials chosen for the elements close to ground. A builder who has not considered it has told you that their extensions create concealed termite pathways — and that yours will too. It is the single most useful question you can ask in this city, and the answer takes thirty seconds.