Knoxfield house

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Revision as of 07:47, 21 April 2008 by Lorraine Hughes (Talk | contribs)
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Solar array
Solar array
Grey water system
Grey water system
Water tank
Water tank
Solar array
Solar array
Smartflo gutter
Smartflo gutter
Additional panels
Additional panels
Shade cloth
Shade cloth

This two bedroom house was designed to be as sustainable as possible on a small suburban block. It was built in 2001. I moved in at the time of my retirement. Entry is via a curved slate path, along a wooden walkway representing a bridge over a dry water course, continuing on slate pavers surrounded by low ground cover of varieties of the herb Thyme. The garden has no lawn, uses Australian natives or plants with low water requirements mulched with coconut fibre.

The large wooden front door is protected by a curved roof, where chains are used instead of downpipes. An open plan living area and study/bedroom are located on one side, and 2 bedrooms, laundry and garage on the other. To the rear is a small Japanese courtyard.

It is passive solar in design, completely self sufficient in water, has a solar hot water service in series with a gas instantaneous boost for the winter months, a grey water recycling system for toilet flushing and garden use, and now produces over 100% of its electricity from a 4.5kW photovoltaic array on the roof.



The long axis of the house runs east - west enabling good solar access through the north facing windows in winter. External blinds made from Soltis fabric supplied by Ace of Shades protect the windows from the summer sun.

Thermal Mass

A concrete slab covered with tiles, give good thermal mass which retains the warmth of the winter sun during the day , and re radiates the heat at night thus reducing heating and energy use. There is less diurnal variation of temperature in an energy efficient house.


During hot periods in summer, the casement windows act like sails allowing the southern breezes to produce good cross ventilation and cooling. Condor vents have no moving parts, and work on the venturi principle.Hot air rises and can escape through these vents if required. The roof space is also vented.


  • The edge of the slab is insulated with polystyrene foam R1
  • Walls apart from aerated concrete blocks insulated with wool/polyester batts R2
  • Loose wool R3 plus additional polyester batts R1.5 and concertina foil in the ceiling
  • Foil sizalation under the colourbond roof
  • Tvek reflective wrap for external stud walls in upstairs bedroom.
  • E-therm ( double sided reflective foil enclosing Low Density Polyethylene Foam) under upstairs bedroom floor and garage door.


All windows are double glazed except the corner ones near the front door where comfort glass is used. The cedar frames do not conduct heat . Most of the windows are located on the north, north-east side with minimal ones facing west and south.

Embodied Energy /Recycled Products

Recycled components included reinforcing steel and slag ash ( a blast furnace byproduct) in the slab, posts in the living area and at the front door, merbu for front decking, jarrah for rear courtyard and bridge, victorian ash for stairs. Radial timber was used for the decking floor and fence, and salvaged timber for the decking posts.In the kitchen reconstituted granite for bench tops and New Age Veneers for cabinets was selected. The cement bricks for garage construction were seconds.

Water Efficiency

  • Rain water is collected via Smart Flow gutters and a first flush water diverter (Team Poly from Pakenham Tanks) in a 6000gallon ( 27,240L )tank. This supplies all the household’s needs - the house is not connected to the mains water supply.
  • Water efficient appliances such as Asko front load washing machine and dishwasher , 3/6 L flushing toilets, AAA shower heads all minimise water use.
  • Grey water (i.e. bathroom water and washing machine water) is passed through an Aquablock Biofilter (2 cubic meters of biologically active peat, which destroys bacteria to Class A water standard). The treatment system is EPA approved. This water is stored in an underground tank, aerated, then used for toilet flushing and the garden. Kitchen and laundry trough water is not reused. Toilets are connected to the sewer.
  • Detergents. Only low sodium liquid detergents are used e.g. Trinature and Melrose products. Bar soaps and washing powders are avoided.
  • Statistics. Water use has been monitored with 2 Kent meters.
  • The water used in 3 years is equivalent to the annual amount used by the average Melbourne household.
  • In 2005 the house was self sufficient in water and saved 75% of the average householder’s discharge to the sewer.

Energy Efficiency / Photovoltaic Array

  • A solar hot water service - Edwards LX 305 -in series with a Bosch 22E continuous flow gas boost during the winter months, provides free hot water for about 7 months of the year.
  • Energy efficient appliances like the Bowin Lo Nox Gas space heater and general use of compact fluorescent light bulbs reduces gas and electricity use.
  • PV Array - 2.4kW Grid interactive system with a small battery bank.
  • 32 X BP275 75W modules attached to the north facing roof at latitude angle i.e. 37 degrees, produce electricity when the sun is shining. Any electricity surplus to the needs of the house is exported to the grid during the day. At night when the sun does not shine , electricity is imported from the grid.
  • PSA 5kW inverter
  • The house has normal 240V wiring.
  • Statistics:
  • The initial 2.4kW PV array produced 55% of electricity needs.
  • The average Melbourne home consumes 6,265kWh per year.
  • In 2005 only 1777kWh was imported from the grid i.e. a savings of 76% of average electricity use.
  • In 2007 and additional array of 12 X 175W Sharp generating an extra 2.1kW of electricity was installed, boosting the total output to 4.5kW
  • With the addition of the second array, the house is a net exporter of energy to the grid - it produces more than is used.


My house is modern, comfortable to live in, being warmer in winter and cooler in summer, collects the water that falls freely from the sky, and uses the sun’s power to produce 55% of electricity requirements thus reducing my ecological footprint and greenhouse gas (carbondioxide) emissions. Global warming is a serious threat to the future of mankind. We can all change our behaviour to minimise the problems. Every little bit can help make a difference. Let’s do it.

Details on water

Rainwater collection

Why allow rain that falls freely from the sky and is becoming a scarce resource, to run off our roof into the storm water system and out to sea? City dwellers expect to turn on a tap and get an immediate and sustained flow of water, without thinking about, or needing to take responsibility for, the collection, storage, and quality of their water.To collect my drinking water, the rain flows through Smartflo gutters which keeps out any leaves, and then through a mesh screen above the Team Poly Water Diverter Mk 2 which is a first flush device system i.e. the first run off from the roof which may contain dust and contaminants does not flow directly into the 6,000 gallon/ 27, 240 L polyethylene tank.

A stainless steel filter is present in the overflow outet pipe to prevent any mosquitos from retro entering my tank from the storm water system. Another 5micron filter is situated under the sink for drinking water.

An SMHP90 Onga pump with 2 X Davey Supercell HP105C pressure tanks allow 100L of water to be drawn off before the pump turns on, thus saving electricity.

Greywater System

Shower and hand basin water plus washing machine water ( prefiltered) is pumped through an Aquaflow Biofilter System i.e. 2 cubic metres of biologically active peat, which destroys bacteria, and is stored in a 3,000L septic tank. Only half the capacity of the tank is available for storage as the greywater enters 750mm below ground level. Kitchen, septic and laundry trough water is not collected for reuse. This system is EPA approved for treating both black and grey domestic waste water. Aeration at the bottom of the tank through a ring of aquapore hose is programmed via a Yasunaga aerator for 3 hours morning and night. A Davey 700HP pump circulates the water to the toilet cisterns and to 4 vandal proof garden taps- coloured purple. The handles are stored separately from the taps to prevent anyone from having access to this water. Signage above the taps warns Recycled water Do not drink

A single pressure tank allows 50L to be drawn off before the pump needs to be activated. This is an energy saving measure so that the pump does not need to pump for every 3 or 6L flush.

Water efficient appliances

In the bathrooms Flexispray AAA shower heads limit the flow of water to a maximum of 9L per minute, and Fowler Florida Toilet suites have a 3/6 L flush.

The Asko Frontload washer W6221 rated AAA uses 61L of water for a normal load, whilst the Asko D1976 Dishwasher also AAA rated uses 17.5L of water.

I have recently done an energy audit on all my electrical appliances in the house and realised that using the dishwasher saves water , and hand washing up saves energy - so there is a trade off between the two.

Cleaning Products

Trinature products are used for cleaning throughout the house because they contain no harmful chemicals to damage the environment. This is particularly important if recycling the water. Trinature washing liquid contains minimal sodium compared to usual washing powders( high salt content) and performs well. Melrose liquid detergent is used in the showers - it is based on virgin olive oil, coconut oil and glycerine and the sodium or salt molecule is replaced by potassium, which is deficient in most australian soils. Bar soaps are avoided as the residue that is left can block filters and pumps.


There is no lawn. Coconut fibre is used for mulching the australian natives and other drought tolerant plants.An Aerobin is a recent addition to my compost bins. It is insulated , thus increasing the temperature of the compost and said to be more effective in killing weed seeds. Air enters from below and is deflected back into the compost , which requires no turning, and can be removed when ready at ground level.

Measurements and comparisons

It took me 3 and a half years to use 240 kL of water. This was the equivalent of the average Melbournian ‘s annual household use at the time. In 1995 this household used a total of 54.5 kL i.e. an average use of 149L /day and of this amount 17.5kL was recycled for toilet flushing.

Compared to the typical Melbourne Home the Knoxfield Sustainable House achieved the following savings in 2005:

  • 100% less mains water
  • 75% less discharge to sewer
  • 63% less electricity
  • 56% less natural gas
  • 68% less greenhouse gas emissions


Australia is the driest inhabited continent on earth. Global warming is a serious threat and changes in weather patterns and reduced rainfall will affect us all. We need to value water as a precious resource, because we can’t live without it and shouldn’t waste it.

We can influence what happens in the future by modifying our behaviour - reducing our energy use, particularly electricity because it is produced from brown coal and produces much of our greenhouse gas emmissions. Consider buying a solar hot water service, installing insulation, converting light fixtures to energy saving compact fluorescents, and installing a rainwater tank. We can all make a difference. Let’s start now.


  • Owner: Lorraine Hughes
  • Sunpower Design Pty Ltd 03 9386 3700
  • Ace of Shades 03 9764 2260
  • Aqua Block Plumbing 03 9752 2209
  • Trinature Pty Ltd 02 4928 2199
  • RJM Sunpower Pty Ltd 03 9435 6376 (PV Array)
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