The Greeny Flat experiment – Small-scale, sustainable, affordable

Andy Lemann shares the principles, materials, results and lessons learnt in building a low-cost, high-efficiency home. Seven months into a one-year trial, the outcomes are promising.

For me, learning to live in harmony with the planet means learning to live without fossil fuels. Before I’m accused of gross hypocrisy, let me be the first to admit that my way of life is highly unsustainable: I drive a car, I eat food grown in faraway places, I use fossil fuels. I certainly don’t have all the answers, I’m simply attempting to take the first steps towards a fossil-fuel-free future. That is what the Greeny Flat is all about.

The Greeny Flat is a full-scale living experiment currently underway on a quiet street in Mittagong in the Southern Highlands of NSW. We’re aiming to see if it’s possible to build a small, comfortable, healthy, energy-positive, low-maintenance, fire-resistant, water-efficient, elderly-friendly infill house at an affordable price. Our two primary aims were to make it energy-positive and affordable.

For 20 years I designed and built sustainable houses in the Rocky Mountains of Montana, near the Canadian border, where the winters get down to -40 °C and the summers up to +40 °C. In that climate, attempting to come even close to net zero energy building is a huge challenge. When I returned home to the NSW Southern Highlands a couple of years ago, it occurred to me that building an energy-positive home here should be relatively easy and inexpensive.

I have since learnt that the cost of most things in Australia is much higher than in the States, so making the Greeny Flat affordable has, in fact, proved to be our biggest challenge. Meanwhile, my partner Cintia and I have lived in the house for nearly seven months, closely monitoring its energy performance, water usage, indoor air quality and comfort levels to see whether it actually meets the initial goals.

The perfect site

The Greeny Flat is designed to meet the future needs of my aging parents who, in their infinite wisdom, had found and purchased an excellent site over 20 years ago. There’s an existing fibro cottage on the east half of the lot that they rent out, which left the west half available for us to build the Greeny Flat.

It is the perfect site for a passive solar home with a gentle slope to the north-east, nice views to the north, and existing buildings and trees to the west and south providing protection from cold winter and hot summer winds. The excellent solar access is also protected by the street to the north, which means that no neighbour can build or plant anything to block our sun in the future.

Just as importantly, this is an infill site in an already-developed area. This helps to reduce sprawl, preserve open space, agricultural land and natural habitats, maximise use of existing infrastructure, and reduce driving.

On that latter point, all the things we use on a regular basis (including shops, schools, medical centres, the town library, parks, playgrounds, hardware stores and trains to Sydney, Canberra and Melbourne) are within easy walking distance of the Greeny Flat, so we could easily live here without a car. To give an indication of how important this is, the average Australian home with two people uses 16 kWh of electricity per day (though the Greeny Flat uses much less). Meanwhile, a commuter, particularly in a regional area like the Highlands, might drive 50 km per day using 40 kWh of fossil-fuel energy.

Another aspect of infill housing that greatly reduces the overall cost is the fact that the land is already paid for. If we had needed to buy the land to build this house, it could have easily doubled the cost of construction. And, since there are very few vacant lots within the established town area, we would most likely have had to build on the edge of town in a new subdivision that used to be bushland or farmland. We’d be contributing to urban sprawl. We’d be paying a lot more. And we wouldn’t be able to live so conveniently close to everything. Thus, infill housing is a good example of a ‘triple bottom line’ benefit, i.e. something that has financial, social and environmental benefits.

KISS

The first rule for building more sustainably is to Keep It Small and Simple. The Greeny Flat has two bedrooms and one bathroom on a 57 m2 footprint. It is a simple, rectangular plan with a gable roof and a concrete slab floor. The kitchen and bathroom are next to each other in order to simplify the plumbing system, and the living spaces face north to make the best use of natural light and sun. The small size means less energy and materials were required for construction, and less energy is required for operation. The simple design made it quicker and more affordable to build, and easier to

Passive solar design

There are two parts to the energy-positive equation. The first, and most important, is energy conservation. By minimising our energy usage we make it much easier and more affordable to produce more energy than we use via renewable energy systems. The primary way that we reduce energy consumption in the Greeny Flat is by using passive solar design principles.

To summarise these principles very briefly: the northerly aspect, window placement, eave overhang, room layout, insulation, air sealing, double-glazed windows, thermal mass floor, summer shading, ventilation, reflective exterior and landscaping are all specifically designed to work together to keep the interior cool in summer and warm in winter without the need for any additional heating or cooling.

In addition to passive solar design, the solar hot water system, low-flow plumbing fixtures and short plumbing runs greatly reduce the amount of energy required to heat water. And the natural lighting, solar clothes drying and energy-efficient electrical fixtures further reduce the overall energy consumption to the point where we can easily meet our requirements with renewable energy.

Because of the experimental nature of the project, we didn’t know when we started what size solar power system would be required for us to be energy-positive. So we chose to install a 3 kW system which, as it turns out, is over twice as big as we really need.

Results

At the time of writing this article, Cintia and I have lived in the Greeny Flat for seven months. Table 1 summarises the results we have recorded so far. In that time, we have exported nearly 2.5 times as much electricity as we have imported, we have used almost as much tank water as town water, and the interior has stayed pretty comfortable with very little in the way of additional heating or cooling (we did occasionally run a small radiator to keep the bedroom warm in the winter).

Admittedly, there were a couple of times when the interior got down below 13 °C when the outside temperature was around -4 °C, which many people would find uncomfortable (we didn’t mind it and simply put on a jumper and some slippers) and a couple of times when the interior got up around 28 °C when the outside was close to 38 °C. But we also made plenty of extra energy so that, if we wanted to, we could run a heating and/or cooling system and still be comfortably energy-positive.

Construction cost

During the design and construction of the Greeny Flat, we carefully weighed the upfront costs against the long-term benefits in terms of reduced operating costs, reduced environmental impact and improved quality of life and community.

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 or profit. In other words, if a builder had built this for us, they would have had to charge more. Table 2 shows the cost breakdown for the project.

The cost per square metre at the end of the table is of particular interest. To put it into perspective, typical building costs in Australia range from about $1000/m2 for the cheapest code-minimum housing, up to $3000/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, or $2630/m2.

We were hoping we could build the Greeny Flat for around $1750/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 (such as kit homes of a similar size) and by the time we add double glazing, extra insulation, solar power, solar hot water, rainwater harvesting, etc, the price always comes out to at least $150,000.

When discussing costs, it is important to remember that housing affordability relates to much more than the upfront 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, the Greeny Flat will save a lot of money by reducing these ongoing expenses.

Operating costs

So far we’ve only had one electricity bill, for June, July and August. The total came to $89.51 which works out to $0.98/day and that was for the coldest three months of the year. Of that total bill, $64.76 was for what they call ‘Supply Charges’ (this is the daily fee that we pay, currently $0.7162/day, just to be connected to the grid) and $14.12 was GST. So we actually only paid $10.63 for the electricity that we used over the three months.

Our bill states that we used 329 kWh for the 91-day period. This is not entirely true because some of the electricity that we use during the day comes directly from our solar power system. What it should say is that we imported 329 kWh from the grid. Our bill indicates that the average usage for a home with two people is 16 kWh/day, so we are taking from the grid around a quarter of the average for comparable homes in our area. And that doesn’t factor in the excess power that we produced from our solar panels and exported to the grid, a total of 823 kWh over the same period—an average of 9 kWh/day. On average, we imported just 3.62 kWh/day, so we exported 2.5 times as much electricity as we imported. Since we don’t have gas or wood-burning appliances, this accounts for our total energy equation in the home for the three-month period.

Lessons learnt so far

Our testing and monitoring of the Greeny Flat experiment will continue for at least one full year so we have a long way to go and lots more to learn. Nevertheless, there are a few lessons that we have learnt already and will probably do differently in the next project, ranging from using a heat pump or standard electric hot water system (enabling us to use our excess PV generation during the day to heat water for use at night; in turn this would reduce the amount of power that we are putting into the grid, and save a significant amount on the initial cost of the system), through to using a termite barrier that would allow us to insulate the slab edge. But more on that down the track! You can keep up with our project at www.greenyflat.com.au and we’re happy to answer questions via the contact form on the website. S