House Extension Costs

How do I know if the cost estimate is high or low?

Many enquiries have mentioned they have received estimates but the estimates have a difference between 30-50%. That’s a large differential that would make you think twice about progressing with your house extension.

Why such a large difference in the house extension cost estimates? How do you compare home extension quotes?

Did everyone receive the same documentation? How much documentation was given to them and at what level was the documentation i.e. concept design, planning or prelim working drawings stage? Was engineering given? Was a PC sum given to use for fittings and fixtures?

What house extension costs were NOT included in their estimate? Did they include demolition, heating, cooling, builder’s profit margin, decks, fencing, driveway?

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?

Who can offer a reliable estimate of building costs?

Many people approach home extension 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:

• Home extension ground floor
• Double storey home extension
• House renovation
• Building a new home

It should also include:

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

Builders Quotes for House Extensions Melbourne

To obtain quotes from builders the documentation needs to instruct builders what to quote. That sounds obvious however the working drawings, structural and civil engineering don’t have 100% of the scope of works for builders to quote.

You want a specification document instructing builders who is to supply items and who is to install those items.

Firstly we need you to decide ‘who’ is doing ‘what’. The scope of work, fittings and fixtures can be:

• Supplied and installed by Builder (B) OR
• Supplied by Owner (O) and installed by Builder (B) or by 3rd Party (3P) OR
• Supplied by 3rd Party (3P) and installed by 3rd Party (3P) or Builder (B) or Owner (O)

To help compare builder’s quotes you may give all builders, whom you have chosen to tender, the same dollar amount to include in their quote for a defined list of fittings and fixtures and that dollar amount to include a 20% builders margin and 10% GST. Otherwise note that the Owner is to supply all fittings and fixtures and Builder or 3rd Party to install.

Home Extension Cost Factors

Building costs for house extensions or home renovations can vary considerably depending on a number of criteria. So it must be customised to your home extension goals to reduce the risk of budget blowouts and help you enter the design stage with clarity and confidence. Important factors that influence your home extension costs are:

• 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
• 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 20-30% 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.

Clarity on these cost factors can greatly improve your home extension results. But there’s one more thing you need to do to avoid unexpected house extension costs. Check your house extension building contract for the order of precedence of documents. This plays a major part in determining which document supersedes other documents if there is a discrepancy in the scope of work once the construction of your home extension commences.

Consultant Home Extension Costs

Don’t forget consultant fees. As an approximate guide, the following fees may be charged by consultants. Based on a home extension estimated at $500,000 requiring a planning permit, you will typically be looking at:

• Architect (creative design, specification and tender and administration): $48,000 – 75,000 depending on experience
• Building designer (creative design, specification and tender): 16,000 – 25,000 depending on experience
• Draftsperson (sparse design development): $8,000 – $11,000 depending on experience
• Land Surveyor: $2,750 – 4,400 depending on the scope of work
• Geotechnical engineer (soil reports): $440 – $770 depending on the scope of work
• Private Town Planner: $5,000 – 12,000
• Structural Engineer: $3,600 – 4,100
• Civil (stormwater) Engineer: $1,600 – 2,000
• Building Surveyor: $4,500 – 5,300

Get Your Home Extension Cost Estimate

With extensive experience, RFT Solutions 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 who specialises in Melbourne home extension design and tendering.

We offer a superior yet simple solution that typically saves a hefty 10-20% on home extension costs. Get in touch with the team today for smart solutions and outstanding results.