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Estimating building costs

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Video: An introduction to construction costs


If there is one thing that both building designers and builders try to avoid until the tender process it is estimating construction costs.

Construction costs can vary greatly depending on:

  • site conditions & location
  • desired levels of finishes
  • building complexity
  • weather conditions during the construction period
  • buying power and business connections

But between having "no idea" and getting a full blown "builders quote" there are very few tools that can help you estimate the cost of your new house or renovation. That's why Home Design Directory has created it's own suite of cost calculators - to help people just like you to estimate construction costs in the very early stages of planning.

Using our construction cost calculator

Home design by Angela Elliss Design

Home Design by Angela Elliss

Keep in mind that our construction cost calculator provides an "estimate" of building costs ONLY. If used correctly the pricing is around 10% + or - the estimated construction cost.

The Cost Calculator is suitable for use before detailed plans have been undertaken. If you have detailed design drawings with correct dimensions, construction details and finishes noted it is worth hiring the skills of a home estimating professional like a quantity surveyor.

If you have developed design drawings, or even better certified construction drawings, you maybe ready to have builders tender on your new home or renovation. If you're a professional building designer or a builder who is asked to provide estimates on a regular basis you may like to download our construction cost calculator app - "Builders Buddy".  Builders Buddy is usable offline and comes with many features including saving files and emailing estimates, see more below.

To get the most accurate results from our calculator you will need to adjust the default /m² costs to a value suitable for your budget & area (labour and materials costs are highly variable within Australia). To get some idea of these costs read the sections below before using the calculator.


1. Cost assumptions

Cost assumptions are built into our calculator and are as follows. These assumptions are easy to change if required. 

  • BASIC /m² rate - A custom designed house on a Excellent site, using basic finishes will have a base cost of $1,500/m². If you are building a project home the /m² costs can be significantly lower - use $1,100/m².
  • STANDARD /m² rate - A custom designed house on a Excellent site,using standard finishes will cost an extra $300/m² ($1800/m²).
  • LUXURY /m² rate - A custom designed house on a Excellent site, using high-end or luxury items such as expensive bathroom or lighting fittings will cost at least $600 extra/m² ($2100/m²).
  • Additions - Additions or extensions are assumed to be double the cost /m² compared to that of new house construction. The reason for this is because there are usually unforeseen structural issues; e.g. termite damage, plumbing problems, and electrical issues. In addition there can be site-access issues, especially if the owners are still living in the house.

2. Site assumptions

Site assumptions have been built into the calculator and are as follows, but are interchangeable.

  • EXCELLENT - If the building site is "excellent" no extra addition is required on the base /m² rate.
  • GOOD - If the building site is "good", add 7% to the base cost of $1,500 (e.g.. slightly sloping block).
  • DIFFICULT - If the building site is "difficult", add at least 20% to the base cost (e.g.. steep block with rocky outcrops and no services).

3. Other

Decks, patios and verandahs - These areas cost on average $900/m². Use a higher value if the outdoor area is to have a roof, or will be constructed more than 900mm off the ground.

Garages costs -  Basic garage space costs an average of $1200/m². Use a higher value if there are any complications such as a sloping block, poor drainage, etc.

Getting detailed construction costs

Licenced builders & quantity surveyors can provide detailed quotes once the design and contruction plans are completed.

Use our free online quotation service to get accurate costs or contact one of our sponsors below:

  • Melbourne - greater area
  • Sydney's North Shore, the Central Coast or the Hunter/Newcastle region -