Start with the Home You Have and the Space You Need
A useful budget covers the new level and the work that connects it to the existing house. Define the layout, have the structure assessed and compare complete proposals. Published builder prices provide context; your own scope and site determine the quote.
Define the scope
Include stairs, services, finishes and changes downstairs.
Check feasibility
Coordinate structural design and the applicable approval pathway.
Compare the budget
Separate quoted work, allowances, exclusions and your reserve.
Plan the household
Agree the schedule, safe access and any relocation.
Define the Addition You Want
Start with the rooms you need and how they will connect to the existing home. Floor area is useful, but it does not describe the staircase, changes downstairs or the finish level a builder needs to price.
| Your brief | Include in the scope | Resolve before detailed pricing |
|---|---|---|
| A bedroom retreat | Bedroom, storage, any ensuite and the stair connection. | Where will the stairs arrive and what changes downstairs? |
| More family bedrooms | Room layout, bathrooms, circulation and storage. | Which rooms and services are included in the proposal? |
| A larger home remodel | The new level and any ground-floor changes or outdoor reinstatement. | Can the work be separated into clearly priced stages? |
Share the same plans and specifications with each builder. Consumer Affairs Victoria's quote guidance explains why a low headline price can leave out the materials or finishes you expect.
Build a Whole-Project Budget
Use written proposals to separate the building contract from other costs you will pay. Ask who supplies each item, whether it is a firm price or an allowance, and what remains excluded.
| Budget item | Scope to identify | A useful question |
|---|---|---|
| Design and assessment | Plans, surveys, structural design and required reports. | Which documents and site investigations are included? |
| Approvals | Applications, permits, inspections and completion records. | Who arranges each step and pays its fees? |
| Building work | Existing-house alterations, upper floor, stairs, roof and access. | Does the price include the connection between both levels? |
| Services and finishes | Bathrooms, electrical work, heating/cooling, windows and selected finishes. | Which products and allowances does the quote use? |
| Site and household costs | Protection, waste, storage, accommodation and reinstatement. | Which costs sit outside the building contract? |
| Contingency reserve | Money set aside for identified uncertainty. | What amount is available, and what would it cover? |
Keep allowances and contingency distinct so the same work is not counted twice. If using a percentage, state the amount it is applied to and check the calculation. Agree a project-specific reserve with your advisers rather than treating a standard percentage as protection against every overrun.
For contract changes, record the work, price effect and any time effect. NSW's contract guidance explains its written variation requirements; the rules for your contract need to be checked locally. A contingency reserve is not automatic permission to charge for every change.
Read Published Builder Guidance in Context
These primary pages were checked on 14 October 2026. Use them to understand the provider and scope behind a published figure, then obtain advice for your property.
| Provider and location | What its page says | How to use it |
|---|---|---|
| Addstyle, Perth | Its 4 February 2026 article gives a second-storey project range of AUD $350,000 to over $700,000, depending on the project. | This is one builder's published Perth guidance, not a national average or an itemised offer. Confirm the exact work, allowances and exclusions. |
| Addbuild, Sydney | It explains why room mix, the existing house and individual specifications limit the usefulness of a generic cost per square metre. | Ask for pricing tied to the documented design; do not turn the guidance into an assumed Sydney premium. |
Neither page establishes a price for your job or a completed Wombat project. A figure from another city cannot be adjusted reliably by applying an unsupported city multiplier.
Check Structural Design and the Approval Path
Have the existing house and proposed addition assessed before settling the design and budget. YourHome advises using a qualified structural engineer to design structural modifications. A home's age or wall material alone does not establish whether it can take another level.
| Local example | Official guidance | Question for your project |
|---|---|---|
| NSW | Complying development can provide a combined planning and construction approval for eligible additions. | Does this proposal meet the conditions, or is another approval pathway required? |
| Victoria | Plans and permits guidance distinguishes planning permission from a building permit. | Which permissions are needed and who will obtain them? |
| Other locations | Requirements depend on the jurisdiction, property and proposal. | What does the local council or relevant building professional require? |
Confirm the applicable height, setbacks, design constraints and required reports with the relevant authority or adviser. Record responsibilities in writing; a nationwide DA rule or a fixed approval deadline cannot establish what applies to an individual site.
Plan the Schedule and Living Arrangements
Ask for separate expectations for assessment, design, approvals, selections, construction and handover. Establish the assumptions behind the dates and how changes or delays will be communicated.
Before work begins, agree:
- Whether the household can stay safely during each stage, with usable access and essential rooms.
- Protection of the existing home and arrangements for weather, dust, noise, storage and service interruptions.
- Temporary accommodation and moving arrangements if needed, using actual local quotes.
- How suspected hazardous materials will be checked before disturbance; see the Asbestos Safety Agency's home guidance.
Ask your insurer how the proposed work and any vacancy affect your policy. Moneysmart explains why exclusions and conditions need checking. Staying home, a fixed rental allowance and a universal construction duration should not be assumed.
Compare Your Options for More Space
Compare building up, extending out, reworking the existing layout and moving against the same household needs. Include the work needed downstairs, the space each option delivers, disruption and the costs outside the construction quote.
Treat resale value as a separate question. Ask a local valuer or property professional to assess the actual property and market; a fixed percentage uplift or guaranteed cost recovery should not decide the project budget.
Before accepting a proposal, check the contracting business's relevant licence or registration, insurance and recent work. The Wombat checks ABNs; homeowners still need to make those checks. Read the Victorian contract guidance as a local example and obtain advice on your own documents.
Our planning guide and extension versus rebuild comparison can help you organise the next discussion.
Sources and Further Guidance
Primary pages checked on 14 October 2026. Provider pricing is attributed context; state guidance applies to its jurisdiction. Confirm current requirements and the actual project scope before committing.
- Addstyle Perth published cost example
- Addbuild Sydney extension budgeting
- YourHome renovations and additions
- NSW complying development
- Victoria plans and permits
- Consumer Affairs Victoria comparing quotes
- NSW residential building contracts
- Consumer Affairs Victoria building contracts
- Moneysmart home insurance
- Asbestos safety at home
