Granny Flat Design Guide

Why design matters

A granny flat is a permanent addition to your property. The design you choose affects everything: council approval speed, build cost, rental income potential, resale value, and whether the space actually works for how you'll use it. This guide walks you through the design decisions that matter most.

1. Layout types

Granny flats fall into three layout families. Each has different strengths depending on your site, budget, and how you'll use the space.

Single-storey linear

Examples: The Darkinjung (1 bed), The Awabakal (2 bed)

Best for: Narrow sites, side-of-house placement, maximum site coverage efficiency

Typical footprint: 5m wide × 10–12m deep

Linear layouts run bedroom(s) and bathroom down one side, open-plan living/kitchen/dining down the other. They're the most site-flexible design — you can fit them into a 5m-wide side yard, orient them lengthways along a rear boundary, or tuck them into an L-shaped corner. Because they're long and narrow, they maximise floor area within the 60m² CDC size limit without needing a wide footprint. Lighting and ventilation work well (windows on both long sides). The trade-off: they feel more corridor-like than square layouts — fine for a rental or short-term accommodation, less ideal if you're designing a permanent home for a parent who values spaciousness.

Single-storey square/compact

Examples: The Wonnarua (1 bed + study)

Best for: Corner sites, properties with wide rear yards, sites where you want to preserve garden space

Typical footprint: 7–8m × 7–8m

Square layouts cluster all the rooms around a central living area. They feel more spacious than linear designs because you're not walking down a corridor — every room opens off the main living zone. They're better for long-term occupancy (aging parents, adult children, home office + guest accommodation). The trade-off: they need a wider site (minimum 8m clear width including setbacks), and they're harder to orient for solar passive design (only two facades get north light, vs. a linear design where you can run the long axis east-west and get north sun into every room).

Two-storey

Examples: The Worimi (2 bed, 2 storey)

Best for: Small sites where you need maximum floor area, properties where single-storey won't fit, areas with good views from upper level

Typical footprint: 6m × 8m ground floor, 50m² upper floor

Two-storey designs are the most space-efficient option — you get 90–100m² of internal floor area on a 48m² ground-floor footprint. That's a full 3-bedroom house in the footprint of a single-car garage. They're ideal for small blocks where a single-storey 60m² flat would eat your entire back yard, or where you want to keep the ground level for garden/entertaining and put the accommodation upstairs. The trade-offs: higher build cost (stairs, upper-floor structure, scaffolding access), harder council approval (some councils have height limits or don't allow two-storey under CDC), and less suitable for elderly occupants or mobility issues.

2. Site considerations

Your site dictates which designs will work. Before you fall in love with a layout, check these five constraints:

Setbacks

CDC requires 900mm minimum side and rear setbacks. That means if you have a 5m-wide side yard, your maximum building width is 3.2m (5m minus 900mm each side). A 5m-wide linear design won't fit — you'd need a 6.8m-wide yard. Measure your available width after setbacks before choosing a design.

Slope

CDC only applies to sites with less than 15% slope across the building footprint. If your yard slopes more than that, you need DA, not CDC — and you'll pay $8k–15k more in approval costs. Sloping sites also add $15k–40k in foundation costs (piers, retaining, cut-and-fill). For steep sites, a two-storey design built into the slope can be more cost-effective than a single-storey design that needs major earthworks.

Solar orientation

North-facing living areas = lower heating costs + better natural light. If your only available site is south-facing, a square layout (windows on all four sides) works better than a linear layout (windows on two long sides only). If you can choose your site, put living areas on the north side of the building and wet areas (bathroom, laundry) on the south.

Access for construction

Can a 3m-wide excavator and a concrete truck get to your back yard? If not, you'll pay $8k–20k extra for hand excavation, crane lifts, or pump trucks. Two-storey designs and linear designs are easier to crane-lift in panels if vehicle access is impossible. Square designs usually need vehicle access for slab pour.

Services (water, sewer, power)

The closer your granny flat is to existing services, the lower your connection costs. If your meter box is at the front of the house and your flat is 40m away at the rear boundary, you'll pay $6k–12k for underground power trenching. Same for water and sewer — every extra metre = extra cost. Check where your existing services are before you pick a site.

3. Connection types

Granny flats can be built as attached or detached. Each has cost and approval implications.

Detached (most common)

Standalone building, separate from the main house. Easier council approval (no fire rating required between buildings, no structural connection to existing dwelling). More flexibility in placement. Typical choice for 90% of granny flat builds.

Attached (connected to main house)

Shares a wall or roofline with the existing house. Can be more cost-effective (one less wall to build, shared roofline, shorter service runs). But requires fire-rated walls between the two dwellings, structural engineer certification that the attachment won't affect the existing building, and sometimes triggers a DA instead of CDC. Only worth it if you're renovating the main house at the same time and can integrate the granny flat into that scope.

4. Finishes and inclusions

All Koori granny flat designs include:

• Kitchen: 900mm gas/electric cooktop + oven, rangehood, stainless steel sink, 20mm stone benchtop, polyurethane cabinetry, tiled splashback
• Bathroom: Wall-hung vanity, semi-frameless shower screen, floor-to-ceiling tiling in wet areas, toilet, exhaust fan
• Flooring: Hybrid vinyl plank (living areas), tiles (wet areas)
• Walls + ceiling: 10mm plasterboard, painted (Dulux Wash&Wear low-sheen)
• Windows: Aluminium sliding windows, keyed locks, flyscreens
• Doors: Hollow-core internal doors, aluminium sliding external door with key lock + flyscreen
• Electrical: LED downlights throughout, double power points (minimum 1 per 6m²), exhaust fans in bathroom + laundry, TV antenna point, NBN conduit
• Climate control: Ceiling insulation (R3.5 bulk + R1.5 foil), wall insulation (R2.5 bulk), ceiling fan provisions (fan not included — owner supply/install)

Optional upgrades

Most common client upgrades:

• Split-system air conditioning (1 unit): +$2,800–3,500
• Stone benchtop upgrade (40mm Caesarstone): +$1,200
• Timber-look vinyl plank flooring upgrade (premium range): +$1,800
• Ensuite instead of shared bathroom (2-bed layouts): +$8,500
• Covered alfresco (3m × 3m): +$6,500–9,000
• Upgraded kitchen appliances (Bosch dishwasher, 900mm oven): +$2,500

5. How to choose your design

Start with these three questions:

Who will live there?

• Aging parent: Single-storey, wide doorways (900mm min), level-access shower, space for furniture they'll bring from their current home → The Wonnarua or The Awabakal
• Adult child returning home: 1-bed layout with study/WFH space, private entry, separate outdoor area → The Wonnarua or The Darkinjung
• Rental income: 2-bed layout maximises rent ($450–550/week vs. $350–400/week for 1-bed), low-maintenance finishes, minimal outdoor maintenance → The Awabakal or The Worimi
• Short-term accommodation (Airbnb): 2-bed layout, high-quality finishes (guests pay premium for new), covered outdoor space, proximity to main house for owner access → The Worimi

What's your site like?

• Narrow side yard (5–6m wide): The Darkinjung (linear, 5m wide)
• Square rear yard (wide but not deep): The Wonnarua (compact square footprint)
• Small block, need maximum floor area: The Worimi (two-storey, 100m² in 48m² footprint)
• Sloping site: The Worimi (built into slope) or pier foundation upgrade on any single-storey design

What's your budget?

• $140k–160k: The Darkinjung (1 bed, simplest build, smallest footprint)
• $165k–185k: The Awabakal (2 bed, single-storey, standard finishes)
• $170k–195k: The Wonnarua (1 bed + study, larger footprint, more internal space)
• $210k–245k: The Worimi (2 bed, two-storey, stairs + upper-level structure)

See the full pricing guide for detailed cost breakdowns and the cost calculator to estimate your specific site.

Next steps

Ready to choose your design? Explore the four named designs:

• The Darkinjung — 1 bed, 5m wide, linear layout
• The Awabakal — 2 bed, single-storey, most popular
• The Wonnarua — 1 bed + study, spacious square layout
• The Worimi — 2 bed, two-storey, maximum floor area

Or get in touch — we'll visit your property, measure your site, and recommend the best design for your situation. No obligation, no cost for the site visit within Central Coast / Lake Macquarie / Newcastle.