Building a New House: Right-Sizing Your Windows

by Greg on June 28, 2013

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A lot of new house buyers agree to have a new house built based on visiting a Builder’s Display Home, and never think about changing the window sizes. In the display house there are usually lots of floor to ceiling windows that are equivalent to 40 – 50% of the floor area.

That’s a lot more than specified in ‘The Building Code of Australia’, which requires you to only have a minimum window area of 10% of the floor area,  with at least 5% of the floor area being openable windows.

Here are some thoughts on why you should consider changing to smaller windows.


In the Display Village fences are normally missing, making the blocks look bigger. In reality for most modern house blocks you could finish up with floor to ceiling windows looking at a 1.8m fence!

How often are you going to be on your hands and knees on the floor and wanting to look out of the windows?

Furniture Placement

You will probably have a fair bit more furniture than in most Display Homes, but unless you want to put it in front of the windows where else can it go?

Heating Costs

You lose 20 times as much heat through a single glazed window rather than brick veneer construction. If your proposed house has 50m2 of windows you could be loosing 7kw/hour of heat on a cold night.

Even with the expense of double glazing you will still be losing 3.5kw/hour.

Summer Cooling

Large East- or West-facing windows get many hours of sun shining in, making the rooms unbearably hot, or costing you a fortune with air conditioning running all day.

Don’t think you will get any benefit with the sun warming those rooms in winter though as those windows will hardly get any sun.

What’s The Good News?

Double glazing is an expensive building element. You may save money on a custom build by having smaller windows. Even many project homes builders will reduce the size of windows as a no cost option as long as you make the decision at the Selection or Pre-Start Meeting.

If you go for an upgraded window option such as double glazing the smaller windows will definitely save you on the initial cost.


I aim to have windows of around 25% of the floor area in South-facing rooms and around 40% in North-facing rooms.

West- or East-facing windows are avoided, or if there is no alternative made as small as possible.


Brian Ashworth

Brian is a Civil Engineer with over 40 years experience in the construction industry. He, and his wife, have had three new houses built. The first in England and the other two in Australia. One of the Australian houses was designed by Brian as a Passive Solar House and the other, a project home, orientated and extensively modified to make the best use of the sun. He has been running the Anewhouse blog for two and a half years.

This post is based on Brian’s latest book ‘A New House Guide to Pre-Start or Selection Meetings’. This extensive guide aims to prepare new builders for all the decisions on details that will turn a house into a home. The guide available as an E-book for $4 and can be purchased on his website.

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