What Actually Happens Before a Builder Starts Your Extension
Most homeowners planning an extension pick up the phone to a builder first. It feels like the natural starting point - you know roughly what you want, you need a price, and a builder is who you turn to for both. The problem is that a builder cannot give you a meaningful price without documentation, and that documentation does not exist yet. The pre-build design phase is where your extension actually begins, and understanding what it involves changes how you approach the whole project.
This guide covers the sequence of work that happens before your builder starts - from the first meeting with a designer through to working drawings, engineering, permits, and the builder appointment. It is written for homeowners at the beginning of the process who want to understand what is involved before engaging anyone. For a more detailed guide specific to Melbourne and the Mornington Peninsula, including the decision between extending and buying, see our home extensions guide.
Why the order of things matters
The sequence of a home extension is not arbitrary. Design comes before documentation, documentation comes before builder quotes, and builder quotes come before construction. Each stage depends on the one before it.
When homeowners skip the design and documentation stage and go straight to a builder, they receive a price that is based on assumptions - the builder's assumptions about materials, subfloor type, window specifications, kitchen scope, finishes grade, and dozens of other variables that have not yet been decided. Different builders make different assumptions, which is why it is common to receive three quotes for the same extension that are many tens of thousands of dollars apart. They are not pricing the same project. They are pricing three different versions of it that exist only in their heads.
Once documentation exists - a full set of drawings, a specifications schedule, an engineering report, and an energy assessment - every builder prices the same scope. The quotes become comparable. Variations during construction reduce, because every decision has already been made on paper. The project has a substantially higher chance of coming in on budget.
This is why the pre-build design phase exists. It is not bureaucracy or delay. It is the work that makes the rest of the project function.
Stage 1 - Engaging a designer
The first engagement in a home extension is with a designer, not a builder. The designer's job is to take the homeowner's goals for the space and turn them into a documented design that a builder can price and build from.
The initial meeting is a conversation, not a brief-taking exercise. A good designer leads the process - asking about how the household uses the space now, what is not working, what the project needs to achieve, and what the realistic budget range is. The homeowner's job at this stage is to bring information, not a prepared brief.
Useful things to bring to the first meeting: the Certificate of Title for the property (available from your state land titles office), any existing drawings or plans of the house, a rates notice or council property information printout, and any correspondence about previous applications or overlays. These help the designer understand the site constraints before any design work starts.
Budget is a practical matter that comes up in the first meeting. You do not need a precise figure, but a realistic range helps the designer shape the concept around what is achievable rather than what would be ideal in a world without limits. A designer who does not ask about budget early is not serving the project well.
Stage 2 - Site analysis and feasibility
Before any design work starts, the designer analyses the site. This goes beyond measuring the block. It includes reviewing the planning zone and any overlays that apply, identifying the required setbacks from property boundaries, checking the maximum site coverage and building height permitted under the relevant planning scheme, and assessing the orientation and topography of the land.
This analysis determines what is actually buildable before a single drawing is produced. It identifies whether a planning permit will be required - which adds time and cost to the pre-build phase - and flags site-specific constraints that will affect the design, such as easements, protected trees, or a Bushfire Attack Level (BAL) rating under the National Construction Code's bushfire construction requirements.
In some cases, specialist reports are needed before design can proceed. A land survey may be required to confirm boundary positions and levels. A soil classification report may be required where there is any uncertainty about foundation conditions. An arboricultural report may be required where protected trees are near the proposed works.
The feasibility work done at this stage prevents problems that would otherwise surface mid-design - or worse, after a permit application has been lodged.
Stage 3 - Concept design
Once the site analysis is complete, the designer produces the concept design. This is where the project takes shape visually for the first time.
A concept design typically includes a floor plan showing the proposed layout of the new space, elevations showing how the extension will look from the outside, and in most cases a three-dimensional model that allows the homeowner to understand how the finished space will feel. The 3D model is where clients tend to make their most important decisions - it is substantially easier to understand scale, proportion, natural light, and connection to outdoor areas in three dimensions than on a flat plan.
The concept stage is where fundamental design decisions are made: how the extension connects to the existing house, where windows and doors go, how outdoor living areas integrate with internal spaces, and how natural light moves through the new rooms across the day. Understanding how to approach these decisions is covered in more detail in our house extension design guide.
Changes at concept stage cost designer time. Changes during construction cost builder time, materials, and rework - charged at rates that make the cost of early design revisions look negligible. Getting the concept right before moving to documentation is one of the most important cost-control decisions in a home extension project.
Stage 4 - Working drawings and construction documentation
Once the concept design is approved, the designer prepares the construction documentation - the full set of drawings and specifications that the builder will price against and construct from. This is the most detailed stage of the design process.
A complete construction documentation package for a home extension typically includes:
Dimensioned floor plans showing all rooms, walls, openings, and fixed elements at a level of detail that allows the builder to set out and construct the work accurately
External elevations showing the appearance of the extension from each side
Sections through the building showing internal heights, floor-to-ceiling relationships, and roof structure
Joinery drawings detailing any built-in cabinetry, benches, shelving, or storage
A finishes and materials schedule specifying all external cladding, internal wall finishes, floor finishes, and ceiling materials
A fixtures and fittings schedule specifying taps, hardware, appliances, and any other selected items
An electrical and lighting layout showing light fitting locations, power point positions, switch positions, and any mechanical ventilation
The specification document accompanies the drawings and sets out the quality standards that apply - the grades of materials, the performance requirements for windows and glazing, the standard of workmanship expected. Together with the drawings, it removes ambiguity and gives the builder a complete picture of what they are being asked to deliver.
This package is what goes to builders for competitive tender. It is also the foundation document for the building permit application. Without it, neither process can proceed properly.
Stage 5 - Engineering and energy efficiency
Two specialist reports are typically produced alongside the construction documentation: a structural engineer's drawings and an energy efficiency assessment.
The structural engineer works from the designer's drawings and produces structural specifications for the components of the extension that carry load - the footings and slab, beams, lintels over openings, roof structure, and the connections to the existing building. For any extension involving structural elements or the removal of load-bearing walls, the structural engineering component is not optional. The building surveyor who issues the building permit will require it.
The energy efficiency assessment confirms that the proposed extension meets the minimum thermal performance requirements of the National Construction Code. For new habitable spaces added to an existing home, this typically involves assessing the performance of the proposed walls, glazing, roof, and floor against the climate zone for the property's location. The assessment is carried out by a qualified energy assessor and the report forms part of the building permit application.
Both the structural drawings and the energy efficiency report are typically coordinated by the designer to ensure the documentation package is complete and consistent before it goes to the building surveyor or to the builders for pricing.
Stage 6 - The building permit
A building permit is required for virtually all home extensions in Australia. It is the approval that confirms the proposed work complies with the National Construction Code and the building regulations of the relevant state or territory. The Australian Building Codes Board develops and maintains the NCC, which applies nationally - each state and territory then administers its own building permit system, with permits issued by registered building surveyors, certifiers, or other designated permit authorities depending on the state.
The building permit is not issued by the designer. In Victoria, building permits are issued by a registered building surveyor; in NSW and QLD the equivalent approval involves a registered building certifier; in WA it is issued by the local government acting as the permit authority. The process and title differ, but the function is the same in each case: a qualified third party reviews the documentation package - including the drawings, structural engineering, energy assessment, and any other required reports - and confirms the proposal is compliant before the permit is issued.
The building permit application is typically submitted by the builder once they have been appointed, using the documentation package the designer has prepared. The permit is a legal requirement before construction can begin. Work carried out without a required building permit is unpermitted building work, which creates title, insurance, and liability problems that can be extremely difficult to resolve.
When you also need a planning permit
A planning permit is an approval from your local council that the proposed works are consistent with the planning scheme for your area. It is entirely separate from the building permit, administered by a different authority, and governed by different legislation.
Many home extensions do not need a planning permit. In residential zones, extensions that meet the standard setback, height, and site coverage requirements of the planning scheme can often proceed without one. In Victoria, this assessment is made against ResCode - the state's set of baseline standards for residential development. Other states have their own equivalent frameworks.
A planning permit is typically required when the proposed works do not meet those standard requirements - for example, when the extension exceeds the permitted wall height or encroaches closer to a side boundary than the scheme allows - or when a planning overlay applies to the property. Common overlay triggers include heritage overlays, neighbourhood character overlays, vegetation overlays, and bushfire management overlays.
The planning permit process adds time to the pre-build phase when it is required - typically two to six months for council assessment, though complex or contested applications can take longer. Identifying whether a planning permit is required should be part of the feasibility work your designer carries out before design starts, so that the permit pathway is factored into the project timeline from the beginning.
Because planning permit requirements differ by state, local government area, and individual site, there is no universal rule about when one is needed. The assessment requires someone who knows the relevant planning scheme - another reason to engage a designer with experience in your area early in the process.
The builder appointment - when it actually happens
Once the construction documentation is complete, the permit pathway is mapped, and the builder quote has been accepted, the builder is formally appointed. This happens later in the process than most homeowners expect.
The documentation package goes to at least two or three builders for competitive tender. Each builder prices the same documented scope, which produces comparable quotes and a genuine basis for selecting a builder - on price, but also on track record, communication, and the sub-trades they work with. The builder then lodges the building permit application (using the documentation package the designer has prepared), obtains the permit, and organises the site for commencement.
From the homeowner's perspective, the builder entering site is not the beginning of the project. It is the moment when months of design, documentation, feasibility work, and approvals become visible as physical change. The work that determines whether the project succeeds - the quality of the design, the completeness of the documentation, the rigour of the permit preparation - is already done.
For an overview of what to expect on the cost side once the process is underway, see our home extension cost guide.
If you are at the beginning of this process and would like to understand how the pre-build phase works in practice, Design Yard 32's residential design service covers the full process from initial brief through to permit-ready documentation. We work with homeowners across Melbourne, the Mornington Peninsula, and Australia-wide.
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A designer first. A builder cannot give you a meaningful price without a design and a documented scope. If you approach builders before documentation exists, you will receive quotes based on different assumptions and no reliable way to compare them. Engaging a designer first is the step that makes the builder tender process work properly.
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A complete documentation package typically includes dimensioned floor plans, external elevations, internal sections, joinery drawings, a finishes and materials schedule, a fixtures and fittings schedule, and an electrical and lighting layout. It is accompanied by a written specification and, for the building permit application, a structural engineering package and an energy efficiency assessment.
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Yes, in virtually all cases. A building permit is required for structural residential work in Australia, including home extensions. It is issued by a registered building surveyor after reviewing the documentation package against the requirements of the National Construction Code and the relevant state building regulations.
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A building permit confirms that the proposed work meets the National Construction Code and the relevant state building regulations. It is issued by a registered building surveyor. A planning permit is an approval from your local council that the proposed works are consistent with the planning scheme for your area. They are separate approvals administered by different authorities. Many extensions require a building permit but not a planning permit - whether a planning permit is needed depends on your specific site, planning zone, and local council.
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In almost all cases, yes. Structural engineering drawings are required as part of the building permit application for any extension involving structural elements - footings, beams, roof structure, or connections to the existing building. The engineer works from the designer's drawings and produces separate structural documentation. The building surveyor will require this before issuing a permit.
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An energy efficiency assessment confirms that the proposed extension meets the minimum thermal performance requirements of the National Construction Code. It is required for any new habitable space added to an existing home and forms part of the building permit application. The assessment is carried out by a qualified energy assessor who evaluates the proposed glazing, wall insulation, roof construction, and floor type against the climate zone of the property's location.
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For a standard single-storey extension, the design and documentation phase typically takes three to six months from the initial briefing to permit-ready documentation. The main variables are the complexity of the project, whether a planning permit is required (council assessment adds two to six months), the time needed to obtain specialist reports such as a land survey or soil test, and the pace of client decisions at the concept stage. Larger or more complex projects take longer.
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Yes - this is the purpose of the construction documentation package. Once the drawings, specifications, engineering, and energy assessment are complete, the package goes to builders for competitive tender. Because every builder is pricing the same documented scope, the quotes are genuinely comparable. This is one of the primary reasons the documentation phase exists: it makes the builder tender process function properly.
