Sept 21, 2014: Greeny Flat Cost Analysis

Two of our primary goals for the Greeny Flat experiment were to try to build a small infill house that was ENERGY POSITIVE and AFFORDABLE. After nearly five months living in the house we’ve made well over twice as much energy as we’ve used so we are completely confident that we’ll meet the energy positive goal over the first year.

As for affordability, there are two important components, the construction costs and the operating costs.

Construction Costs

In total the Greeny Flat cost $128,000 to build and that has to be considered as COST PRICE, i.e. all the materials, subcontractors, and our own labour has been included with no markup for overhead and profit. In other words, if a builder had built this for us they would have had to charge more (we will go into this in more detail later). The table below is the cost breakdown for the project.

GF cost analysis

The cost per square metre number at the end of the table is of particular interest. To put it into perspective, typical building costs in Australia range from about $1,200/m2 for the cheapest code minimum housing, up to $3,000/m2 and more for the highest quality, custom homes. So we’re somewhere near the middle. Realistically, if a builder were to build this house and make a profit they would have to charge at least $150,000 which would be $2,630/m2.

We were hoping we could build the Greeny Flat for around $1,750/m2 (i.e. total cost under $100,000) so we clearly have a lot of work to do to reach that goal. On the other hand we’ve looked at a number of other options (like kit homes of a similar size) and by the time you add double-glazing, extra insulation, solar power, solar hot water, rainwater harvesting, etc, etc, the price always comes out to at least $150,000.

One shining exception to this is a house that was built in Bundanoon just over a year ago by Glenn and Lee Robinson. They had very similar goals to the Greeny Flat when they started and have met the affordability goal admirably. According to Glenn they built their house for just under $1,500/m2 and they are also making nearly twice as much energy as they are using. Here is a link to a recent article about their project from our local newspaper.

Part of the reason the Greeny Flat cost is higher per square metre is because it is only about half the size. A smaller house still has many of the same costs as a larger one (e.g. electricity, water, and sewer connections, kitchen, bathroom, etc) so the cost per square metre tends to be higher even when the overall cost is lower. Another reason is that the Greeny Flat is much more experimental. Nevertheless we have already learned a lot from Glenn and Lee’s project and look forward to implementing those lessons in our next project. Meanwhile Glenn and Lee are just about to start building their own granny flat and it will be fascinating to see how the costs work out for their smaller building.

Operating Costs

Because we are making a great deal more energy than we are using in this all electric house, and because the house was built to require very little maintenance, our operating costs are VERY low. So even though the Greeny Flat cost a bit more than a ‘standard’ project home to build, over time it will save us a great deal of money which is a very important (and often overlooked) component of affordability. To see a table of our actual running costs to date, please visit our Results Page.

When discussing costs it is important to remember that housing affordability relates to much more than the up-front construction cost. Over the life of a typical home there will be at least as much spent on running costs like electricity, gas, water, and maintenance. So, in the long-term, both the Greeny Flat and the Robinson’s house will save a LOT of money by reducing these ongoing expenses.

To illustrate this point, see our Newsletter article: $10.63 Worth of Energy in 3 Months.

2 comments to Sept 21, 2014: Greeny Flat Cost Analysis

  • Christopher Herde

    In your cost analysis, could you calculate the cost to construct a 3 B/R, 2 bathroom cottage with a total floor area of 100m2? Exclude garage & external patios from your costings.

    Did you have the frames & trusses made locally?

    I live locally in the SH and am most interested in your project.


    • admin


      Based on the Greeny Flat and a few other projects in our area we’re finding that you can build an energy positive home for between $1500 and $2000/sqm. Given that you want to fit three bedrooms and two bathrooms into a relatively small house you should count on being towards the high end of that range. This assumes that you keep all of the fixtures and finishes simple and cost effective, in which case $200,000 is doable.

      We had our frames (there are no trusses) made by Oxley Timber in Bowral but I drew every stud in every wall to ensure that they built them the way I wanted them. They almost got everything right.

      I would be happy to show you the Greeny Flat some time and explain how it works if you’re interested.


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