House Extension Costs

Home extension costs Melbourne

House Extension Costs In Melbourne

How much is my Melbourne house extension, home renovation, new home going to cost me? This is the question most frequently asked when people reach out for our services.

An estimate of building costs from a quantity surveyor or experienced building estimator can prove extremely useful once you have a concept design, soil report and description of materials and fittings & fixtures. Naturally, you do not have this documentation at the beginning however it still makes sense to obtain an estimate of building costs before you commit to pay fees to a building designer, draftsman or architect.

An estimate of home extension costs can be provided by a reliable source based on current floor area rates for ground and first floor extensions plus demolition costs, builders preliminaries, builders margin then add GST then compared with building costs from previous projects within the last 12 months and averaged out. This combination of costings can be used to help determine if your budget is close to the mark before you commence paying a building designer, draftsman or architect.

How do I know if the cost estimate is low?

Can they tell you what works have been estimated and from where they obtained their figures i.e. what is the origin of their figures for the estimate they have given you?

For a home extension did the works they estimated include more than just the cost of the new build portion – new construction – of works? Did they include the deck or any changes to the existing roof, are windows double glazed or linen and storage cupboards included as well as built in robes, demolition of existing part of your home, consideration on whether your existing home is on stumps or a concrete slab, the ground slope, materials, the builders preliminaries and profit margin.

If your project is a house renovation then what works were included – i.e. new flooring – timber, carpet or a combination of both, the restumping of how many rooms, internal walls removed or newly constructed, windows removed and/or repositioned, bathroom and or kitchen renovation, are any plumbing fixtures moved and is the home on stumps or a slab, new fittings & fixtures, plaster repairs, painting etc?

Be aware that you get what you pay for. If you obtain an estimate free of charge then you may not be getting a reliable estimate of building costs. Anyone who has the time to offer a free estimate of building costs cannot have much work or they may be very busy because they offer a low estimate of building costs in order to convince you to work with them. Be cautious of a low estimate as you may end up paying fees to your building designer, draftsman or architect for a house extension you cannot afford.

Who can offer a reliable estimate of building costs?

No reliable source in the industry will offer you a building quote for construction because it is impossible to quote without finished working drawings, engineering, a list of materials, fittings and fixtures and other items also. However, a reliable source can offer a reliable estimate.

If you pay for the estimate and they can tell you what works will be estimated and from where they obtain their figures then you can place more trust in what you are receiving.
Many people approach builders seeking an estimate however most good quality builders are extremely busy working on current projects and quoting projects from architects or building designers who have given them the finished working drawings, engineering etc. A good quality builder will tell you to get drawings prepared by an architect or building designer.

A superior estimate is based on different square metre rates for:

It should also include:

  • Demolition costs & builders preliminaries and any site costs
  • Fittings & fixtures
  • Builders profit margin

Building costs for house extensions or home renovations can vary considerably depending on a number of criteria.

  • Choice of building materials- slab versus stumps, metal roof versus concrete tiles, lightweight cladding versus brickwork, fittings and fixtures – bathroom and kitchen tap fittings, tiles, window frames, double glazing, heating & cooling, lighting
  • The size of the extension obviously affects the cost
  • The extent of client involvement – does the client choose to perform any of the building works such as painting
  • Commencement and duration of the building works – does the project extend over the Christmas holiday break or during seasonal busy periods – this will add to any interest cost and/or rental costs if you need to move out
  • Seasonal building market conditions – the number of rain affected days – this will add to any interest cost and/or rental costs if you need to move out
  • Town planning delays – this can result in additional costs and potentially add months to your home extension or house renovation.
  • Access to the building site – no parking or access to the rear only through the front door will increase labour costs
  • Size and competence of the selected building firm or builder – the bigger the business the more overheads and, by necessity, will pass this cost on to you and increase the builder’s quotes
  • Each builder’s quote will factor in a different profit margin at anywhere from 10-30% or more.
  • Soft landscaping
  • Varying professional fees – architect, draftsperson, town planner, structural engineer, soil report, building surveyor, etc.
  • Abnormal ground conditions requiring additional site costs – a sloping block and/or the need to dig deeper to reach solid ground and so concrete pours will vary.

Consultant Home Extension Costs

Don’t forget consultant fees. As a rough guide, the following fees may be charged by consultants. Based on a home extension estimated at $300,000 requiring a planning permit, you will typically be looking at:

  • Architect (creative design as per planning and building regulations): $25,000 – 45,000 depending on experience
  • Building designer (creative design as per planning and building regulations): 12,500 – 15,500 depending on experience
  • Draftsperson (draws what they are given – no design involvement): $6,600 – $8,800 depending on experience
  • Land Surveyor: $2,750 – 3,850 depending on the scope of work
  • Geotechnical engineer (soil reports): $440 – $550
  • Private Town Planner: $5,000 – 10,000
  • Structural Engineer: $2,750 – 3,850
  • Building Surveyor: $2,750 – 3850

With extensive experience, RFT Solutions Melbourne building designers can provide an estimate of home extension costs based on floor area rates and building costs from previous projects in the past 12 months.

Your home extension, house renovation, new home will be one of the largest financial investments you will make therefore it makes sense to engage a reliable professional.

RFT solutions can help with your building cost estimates, so get in touch.


If you're building a new home, house extension or renovation, RFT Solutions offer peace of mind. Our goal is to save you time, money and achieve a result you love. Contact us today (03) 9421-2222 for a free consultation.