How Much Does a House Extension Cost?

The cost of building a house extension varies from $965 to $2,710 per square metre. This applies to 50m2 to 150m2 ground and upper floor extensions.

For a single-storey extensions can cost from $1,350 to $2,100 per m2. However, price may change depending on the design, area, and materials.  If you want a two-storey house extension, it might cost around $3,150 per m2 or more.

Prices for labour and other inclusions must also be considered. A clearly defined plan will help you to determine project specifics and the expected cost of each element required for house extensions.

Expect to pay more for extension projects requiring foundation works, engineering assessment and major structural alterations. Find a home extension builder to work in a timely and professional manner to ensure the quality of construction.

Before the actual construction commences, make sure to finalise the design specifications. Initial consultations are done to properly lay out your costings.

Cost of House Extension Contractors

Most home extension builders subcontract electricians, plumbers and carpenters to handle the project. They collaborate with tradies to speed up the process and make the space liveable.

Here are the average hourly rates of tradies to give you an overview of how they charge (Note: Prices are inclusive of overheads and profits).

• Electrician: $79 – $125 per hour
• Plumber: $78 – $125 per hour
• Bricklayer: $69 – $107 per hour
• Carpenter/Joiner: $68 – $107 per hour
• Painter/Glazier: $68 – $107 per hour
• Tiler: $45 – $65 per hour

Note: Price estimates are based on Rawlinsons’ Australian Construction Handbook 2018, Edition 36. HIREtrades is a marketplace of local house extension builders providing homeowners with quotations based on their needs and budget.

What Determines the Cost to Extend a House

Homeowners have individual needs and requirements when planning for a home extension. Here are a number of factors that determine the cost of building an extension.

1. Site preparation

A ground floor (or single storey) extension is more likely to require preparation work including site assessment (i.e. soil condition, level), demolition and excavation. The more complex the job is, the more you will be charged.

Home extension builders will also have to check the area for accessibility issues and other complications. These aspects will affect how they will price the job.

2. Scope of work

The lesser structural work required, the fewer costs will be incurred. Minimise expenses on supplies by reusing existing fixtures for your expanded home. Otherwise, new plumbing and electrical fittings can have an impact on pricing.

If your outdoor space is less likely to accommodate a home extension, then a second storey addition might be the closest option. Any structural amendments done to support the weight of the upper floor may reflect on your extension costs.

3. Type of home extension

Are you adding a second storey or a single-storey extension? Building a first floor (or second storey) extension may cost less as it doesn’t require excavation work or ground preparation.

Additionally, for those homeowners with larger properties or looking to optimise rental income, considering the construction of a duplex house or adding a duplex extension can be a strategic choice. A duplex essentially consists of two separate living units, either side-by-side or stacked one above the other, each with its separate entrance. This type of extension or building offers the opportunity to generate rental income or cater to extended family living comfortably on the same property.

Extending upwards would mean replacing the roof of your house and adding new floors to accommodate the second-storey extension. Installation of external wall cladding, windows and roofing systems also attract increased costs.

4. Quality of materials

Good quality materials generally cost more than standard ones. For instance, custom bathrooms with high-end fixtures (e.g. loo, bath) can be more expensive than standard fit-outs.

The quality of floor additions, lightings, furnishings and furniture significantly influence the final cost.

5. Council fees

Building restrictions vary per State. Prior to construction, consult with your local council to confirm requirements. Complying with height restrictions and neighbouring boundaries will save you from future disputes.

Council approvals may have associated fees which add to your house extension cost. Many builders assist you with all council dealings to reduce your worries and smooth out the construction process.

The Cost of House Extensions per square metre

The size of the structure and nature of work will determine the extension costs per square metre. Check the indicative costs of ground and upper floor extension projects for your reference.

For a tiled roof, medium standard finish ground floor addition, consider the following price range:

Add around $1,800 to $27,500 each for bathroom fit-outs and services. For kitchen fit-outs, expect to pay anywhere between $15,500 to $23,000 each.

For a tiled roof, medium standard finish upper floor extension, expect to pay the following amount:

Bathroom fit-outs and services will cost you about $18,000 to $27,500 each.

You also have the option to have your existing home renovated depending on the need. Here’s what to expect:

• Bathroom renovation: $5,000 to $35,000
• Kitchen renovation: $10,000 to $45,000
• Bedroom renovation: $25,000 to $35,000
• Dining room renovation: $2,000 to $20,000

Compile the expected in a spreadsheet or online software to keep track of your expenses. Always consult with a home extension builder to know what project will suit your budget.

Note: Price estimates are based on Rawlinsons’ Australian Construction Handbook 2018, Edition 36.

How to Hire a Professional Builder for House Extension Projects

Moving to a larger house considerably costs higher than extending an existing home. When planning for a home extension, consider the amount of professional fees that you have to pay. These may include:

• Building regulations
• Structural evaluation report
• Building estimator
• Design (interior)
• Draftsman
• Land surveyor
• Soil condition report (conditional)

Prior to construction, check if the builder’s expertise is focused on residential extensions. Request for sample works to help you choose.

Most importantly, verify their credentials. Ask to see a copy of their updated licence and insurance to help protect your finances.

Read online reviews and check customer references. Their experience also determines the quality of home extension works.