A feasibility check is an evidence-based decision about whether a granny flat concept is lawful, physically workable, serviceable and financially tolerable before detailed design or a building contract. It is not a free quotation with a floor plan attached. The site can defeat an otherwise attractive design through an easement, sewer, flood level, bushfire requirement, protected tree, steep access route or lack of compliant private open space.
The best early question is not “Will a two-bedroom model fit in the backyard?” It is “What is the usable building envelope after every verified constraint is plotted?” This checklist helps a homeowner move from a street address to a defensible go, redesign or stop decision.
Jurisdiction and currency note — 11 September 2026: This is general Australian information, not legal, planning, surveying, engineering, building-certification, tax or financial advice. Planning controls, hazard maps, utility records and adopted construction requirements change. Verify the current position for the legal lot with the relevant authorities and appropriately qualified professionals before committing funds.
1. Confirm the project brief
Write down who is expected to live there, for how long and with what needs. A dwelling for an older parent may need step-free access, generous circulation and visual connection to the main home. A long-term rental may prioritise privacy, acoustic separation, a defensible entrance and practical waste storage. A home office with occasional guests may not legally qualify as a dwelling if it lacks or avoids required residential facilities.
Set three levels:
- must have: lawful use, bedroom count, accessibility, budget ceiling;
- strong preference: orientation, parking arrangement, storage, private outdoor area;
- optional: premium finishes, additional deck, bespoke roof form.
This prevents optional features from consuming the only workable area or budget.
2. Verify the land before measuring the yard
Obtain a current title and registered plan from the relevant land registry. Official starting points include Property and land titles information in Victoria and Property titles, valuations and surveys in Queensland. The title may reveal easements, covenants or other dealings, but it is not a substitute for a survey or legal interpretation.
Commission a feature and level survey when the initial desktop screen is promising. It should identify boundaries, existing structures, significant trees, levels and visible services. Ask whether further title re-establishment or service-location work is needed. Fences, sheds and online aerial imagery can be displaced from legal boundaries.
Record:
- lot and deposited, plan or survey-plan identifiers;
- ownership and any strata, community or body-corporate context;
- easements, covenants and restrictions;
- boundary dimensions and encroachments;
- existing house approval status if uncertain.
3. Establish the planning envelope
Use an official address-based system, such as the NSW Planning Portal Spatial Viewer or Victoria’s Planning property report, to identify zones and mapped controls. Then verify the result against the current legal instrument and council information. A map is an investigation tool; it is not an approval.
Check the statutory definition of the proposed dwelling, whether a principal dwelling must already exist, permissible floor area, minimum lot conditions, setbacks, height, site coverage, landscaped area, private open space, parking and access. For example, NSW homeowners should begin with the official secondary dwellings framework, but must still test the property and proposed pathway.
Create a simple constraints plan. Draw the lot, existing home, required setbacks, easements, major trees, service corridors, vehicle route and hazard-affected areas. The remaining shape—not the total backyard—is the preliminary buildable envelope.
4. Screen hazards and environmental constraints
Check official mapping and council records for:
- bushfire-prone land and required construction or access responses;
- flood planning levels, overland flow paths and evacuation issues;
- coastal, landslip or erosion controls;
- contamination or potentially contaminating former uses;
- heritage items, conservation areas or archaeological sensitivity;
- biodiversity, watercourse and vegetation controls;
- acid sulfate soils or other jurisdiction-specific layers.
Do not convert a mapped risk into your own technical conclusion. A map may trigger a bushfire assessment, flood certificate, geotechnical report, arborist report or contamination investigation. Obtain the report early if its outcome could eliminate the preferred location or materially change cost.
5. Find the services
Desk records are a starting point, not a precise excavation plan. Identify electricity, water, sewer, stormwater, gas and telecommunications. Determine where the new dwelling would connect, whether capacity is available, who owns the asset and what clearances apply. Ask the relevant authority or hydraulic designer whether building over or near infrastructure is restricted.
Stormwater deserves early attention. A site may have room for a building but no simple lawful discharge point. Retention, detention, charged lines, pumps or drainage easements can materially affect design and maintenance. Likewise, a long or constrained sewer route can change floor levels and the viable position of wet areas.
Keep utility plans, authority responses, locator evidence and design assumptions in the feasibility file. Never rely on “services should be near the back fence.”
6. Test access and construction logistics
Measure the narrowest route from the street to the proposed work zone, including eaves, meters, air conditioners, gates, trees and changes in level. Consider workers, excavation, concrete delivery, cranes or modular components, spoil removal and material storage. A design may fit after construction but be unusually expensive to build because machinery cannot reach it.
Also test permanent access. Can residents and emergency responders reach the dwelling safely? Is the path well lit, drained and suitably graded? Can bins be moved without crossing private living areas? Is there space to maintain walls, gutters and services after completion?
7. Test building performance, not only footprint
The National Construction Code is Australia’s primary set of technical design and construction provisions, subject to jurisdictional adoption and variations. A certifier or building surveyor should identify the applicable edition, classification and required documentation. Early design must allow for fire separation, structural support, weatherproofing, ventilation, energy efficiency, sanitary facilities and safe access.
Orientation also affects feasibility. The Australian Government’s Orientation guidance explains how solar access, prevailing conditions and room placement influence comfort and energy performance. A slightly smaller, well-oriented plan can outperform a larger plan that blocks winter sun, overheats or destroys the amenity of the principal home.
8. Build a realistic cost range
Separate the building price from total project cost. Allow for:
- survey, design and engineering;
- planning, building and authority fees;
- demolition, tree work and hazardous-material management;
- excavation, retaining, drainage and foundations;
- service connections or upgrades;
- access constraints and temporary protection;
- energy assessment and approval conditions;
- landscaping, paths, fencing and external works;
- finance, insurance, tax advice and contingency.
Use ranges while information is incomplete. A quote based on an assumed flat, clear and serviced site should not be treated as the likely final cost for a constrained property.
Practical decision sequence
- Complete the brief and budget ceiling.
- Obtain title, plan and desktop planning information.
- Mark obvious fatal constraints.
- Commission the survey and locate services.
- Prepare a measured concept and pathway matrix.
- Obtain targeted hazard and engineering advice.
- Price the whole scope with exclusions exposed.
- Ask a planner and certifier to confirm unresolved assumptions.
- Decide: proceed, redesign, defer or stop.
Evidence checklist
Your feasibility pack should contain:
- project brief and must-have list;
- title, registered plan and relevant dealings;
- feature and level survey;
- official planning report and current clause extracts;
- preliminary constraints and building-envelope plan;
- service searches and written authority advice;
- hazard reports where triggered;
- measured concept with floor area, setbacks and levels;
- planning and building pathway advice;
- preliminary structural, drainage and access assumptions;
- itemised cost range, exclusions and contingency;
- decision register showing what is verified and unresolved.
Warning signs
- The designer measures from fences without a survey.
- A title easement is ignored because no pipe is visible.
- The concept fills the nominal maximum area before site coverage and open-space checks.
- Flood or bushfire mapping is dismissed as “usually fine.”
- Services are shown without records, locating or authority confirmation.
- The quote excludes retaining, stormwater, upgrades and approval conditions.
- A prefabricated unit is presented as bypassing planning or building law.
- The main house loses required light, privacy, access or usable outdoor space.
Questions to ask before proceeding
What exact legal definition and approval pathway applies? Which item could make the project impossible rather than merely expensive? What information is surveyed, what is mapped and what remains assumed? Who confirms sewer and stormwater feasibility? Which costs are excluded? Which design choice protects accessibility and future use? What happens if the approval authority requires a smaller footprint or different location?
Source hierarchy
Prioritise current legislation and planning instruments, official land-registry records, address-specific government mapping, written council and utility advice, surveys and reports by registered professionals, then supplier material. Treat online estimators, generic plans and neighbouring projects as leads only.
AMESCORP disclosure and limits
AMESCORP has a commercial interest in helping homeowners assess and potentially procure granny-flat projects. Its content may support enquiries about AMESCORP services. Homeowners should independently verify material decisions and obtain advice appropriate to their site.
AMESCORP provides no guarantee of approval, site suitability, service capacity, price, programme, rental income, valuation, tax treatment or investment return. Feasibility remains provisional until the responsible authorities and professionals have accepted the required evidence.
Reviewed official sources
These are the first-party and authoritative references reviewed for this article.
- NSW Planning Portal Spatial Viewer — NSW Planning Portal; accessed 2026-09-11.
- Planning property report — Victorian Department of Transport and Planning; accessed 2026-09-11.
- Property and land titles information — Land Use Victoria; accessed 2026-09-11.
- Property titles, valuations and surveys — Queensland Government; accessed 2026-09-11.
- Secondary dwellings — NSW Department of Planning, Housing and Infrastructure; accessed 2026-09-11.
- National Construction Code — Australian Building Codes Board; accessed 2026-09-11.
- Orientation — Australian Government Your Home; accessed 2026-09-11.