Kit or flat-pack granny flats
Pre-designed modular structures delivered to site in panels or sections and assembled on a prepared slab. Kit homes are manufactured off-site in controlled factory conditions and transported to your property. They typically include frames, wall panels, roof trusses, windows, doors and external cladding. Electrical, plumbing and internal fitout are completed on-site by licensed trades.
Typical cost: $120,000 to $180,000 supply and install for a 60sqm two-bedroom kit on a flat site including slab and basic services. Site costs, service connections and council fees are additional.
Pros
- • Faster construction timeframes (six to ten weeks on-site after slab)
- • Fixed pricing reduces variation risks and budget blowouts
- • Factory construction improves quality control and weather independence
- • Lower labour costs compared to custom builds
Cons
- • Limited design flexibility and customisation options
- • Standard layouts may not suit irregular or sloping sites
- • Transport costs increase for remote locations (over 100km from factory)
- • Some councils scrutinise kit homes more closely in heritage or character zones
Best for: Homeowners prioritising speed and budget certainty on straightforward flat sites with standard service access. Good for rental income projects where design uniqueness is less important than functional layout and quick turnaround.
Custom designed and built granny flats
Fully bespoke granny flats designed by an architect or building designer to suit your specific site, requirements and aesthetic preferences. A licensed builder constructs the flat on-site using traditional building methods. This approach offers complete flexibility in layout, materials, finishes and architectural style.
Typical cost: $2,200 to $3,500 per square metre including design fees, quality fixtures and custom details. A 70sqm custom granny flat typically costs $160,000 to $250,000 complete with all services and council approvals.
Pros
- • Tailored design maximises site potential and addresses constraints
- • Choice of all materials, fixtures and finishes to match main house
- • Better integration with existing landscaping and site features
- • Potential for higher quality construction and unique design elements
Cons
- • Higher costs (typically 20 to 40 per cent more than kit or modular)
- • Longer construction timeframes (sixteen to twenty-four weeks on-site)
- • Greater exposure to variations and cost overruns during construction
- • Requires more owner involvement in selections and decision-making
Best for: Homeowners with challenging sites (steep slopes, narrow access, bushfire zones), those wanting architectural quality matching a high-end main residence, or projects where unique design adds significant property value.
Modular or transportable granny flats
Fully constructed modules built in a factory and delivered to site as complete or near-complete units. These differ from kit homes because they arrive substantially finished (flooring, kitchens, bathrooms, wiring and plumbing installed). The modules are craned onto prepared foundations and joined together if multi-module, with final connections and finishing completed on-site.
Typical cost: $140,000 to $200,000 delivered and installed for a 60 to 70sqm modular unit including slab, crane and service connections. Transport costs rise significantly beyond 200km from the factory.
Pros
- • Fastest installation (one to three days on-site for placement and connections)
- • Minimal site disruption and neighbour impact during installation
- • Very high quality control due to factory construction environment
- • Can be relocated if you move (subject to engineering and transport costs)
Cons
- • Transport and crane costs increase overall price, especially for wide loads requiring pilot vehicles
- • Access requirements are strict (minimum 3.5m width, overhead clearances)
- • Limited floor plan options compared to custom builds
- • Some councils impose stricter appearance standards for transportable buildings
Best for: Homeowners needing very fast installation timelines, sites with good vehicle access but difficult working conditions for extended construction periods, or situations where future relocation is desirable.
Converted garage or shed granny flats
Transforming an existing garage, shed or outbuilding into a habitable granny flat by adding insulation, internal walls, plumbing, electrical, heating and cooling. This approach reuses an existing structure but requires substantial work to meet building code requirements for habitable spaces including ceiling heights, natural light, ventilation and accessibility.
Typical cost: $60,000 to $120,000 for a full conversion of a 50 to 70sqm garage including insulation, lining, kitchen, bathroom, flooring, heating/cooling and all service connections.
Pros
- • Lower costs than new construction (typically 40 to 60 per cent less)
- • Faster council approval if structure is already approved and compliant
- • Existing foundations and roof reduce structural work required
- • Avoids losing existing garage or storage space by building new elsewhere
Cons
- • Existing structure may not meet habitable room requirements (2.4m ceiling height)
- • Older buildings may have asbestos, poor waterproofing or structural issues
- • Floor levels and existing openings limit optimal layout and design
- • Insulation and services retrofitting can be more complex than new construction
Best for: Budget-conscious homeowners with a suitable existing structure, properties where site constraints prevent new construction, or situations where retaining existing garage or shed function is not critical.
Studio or one-bedroom granny flats
Compact secondary dwellings of 40 to 60 square metres with combined living, sleeping and kitchen areas and a separate bathroom. Studio layouts offer open-plan living with the bedroom defined by furniture placement or partial dividers rather than walls. One-bedroom versions include a separate bedroom with door.
Typical cost: $1,800 to $2,800 per square metre fully fitted. A 50sqm studio or one-bedroom granny flat costs $90,000 to $140,000 complete including basic landscaping and services.
Pros
- • Lower construction costs due to smaller footprint ($100,000 to $150,000 typical)
- • Easier to achieve complying development status in many councils
- • Reduced ongoing costs for heating, cooling and maintenance
- • Sufficient for single occupants or couples without children
Cons
- • Limited appeal for families or long-term rental to multiple occupants
- • Less rental income potential compared to two-bedroom configurations
- • Storage and living space can feel cramped for extended stays
- • Lower resale value contribution compared to larger granny flats
Best for: Accommodation for a single elderly parent, home office or retreat, short-term rental income (Airbnb), or maximising returns on smaller blocks where space is constrained.
Two-bedroom granny flats
The most common granny flat configuration, typically 60 to 90 square metres, including two separate bedrooms, a bathroom, open-plan kitchen and living area, and laundry facilities. This size comfortably accommodates couples, small families or provides flexibility for multi-generational living or rental income.
Typical cost: $2,000 to $3,200 per square metre fully completed. A 70sqm two-bedroom granny flat with quality fixtures costs $140,000 to $220,000 including all services, slab and landscaping.
Pros
- • Broad market appeal for long-term rental or family accommodation
- • Higher rental income (typically $350 to $550 per week depending on location)
- • Provides flexibility for offices, guest rooms or changing household needs
- • Better property value uplift compared to studio configurations
Cons
- • Higher construction costs ($150,000 to $230,000 typical range)
- • May exceed complying development thresholds in some councils requiring full DA
- • Requires larger site area and may trigger additional parking requirements
- • Higher ongoing costs for utilities and maintenance
Best for: Maximising rental income, accommodating elderly parents with a carer, adult children living at home, or adding substantial value to your property for future sale. The most versatile and saleable configuration.
Dual-key or attached granny flats
Secondary dwellings that share a common wall or are partially integrated with the main house but have separate entrances, living areas and services. These configurations can include internal connecting doors that can be locked for complete separation. Common in townhouse-style developments on larger blocks.
Typical cost: $1,700 to $2,800 per square metre due to shared wall savings. A 65sqm attached two-bedroom granny flat costs $110,000 to $180,000 complete.
Pros
- • Reduced construction costs by sharing walls and services (10 to 20 per cent saving)
- • More efficient use of site coverage and setback requirements
- • Internal access option provides flexibility for family use or rental
- • Shared driveways and entry paths reduce site costs
Cons
- • Noise and privacy issues more prominent than detached granny flats
- • Sound insulation requirements increase construction complexity and costs
- • Some councils impose stricter design standards for attached secondary dwellings
- • Rental income may be affected if tenants perceive less privacy
Best for: Multi-generational families wanting proximity with privacy, smaller blocks where detached construction is not feasible, or maximising yield on inner-city or high-value sites where land efficiency is critical.
