Building design
Orientation
The building is oriented along a North-South axis, offsetting it from the site.
Building-site interface
The building connection to the ground was designed to be minimal, to reduce the need for earthworks and maintain habitats for local flora and fauna. The house is founded on concrete footings. Excavation was required for the placement of the two large water storage tanks, and slabs were poured for the carport and laundry.
Landscaping
Approximately 1/3 of the 480m2 site has been planted out in locally sourced natives. The garden strongly favours fruiting species to support the bird population in the neighbourhood, which otherwise has only sparse vegetation. Topsoil was imported to establish the garden on the sandy site, and a subsurface irrigation system was installed to reduce evaporation losses.
The building plan is based on two double storeyed units, which are connected by a double height breezeway. The breezeway is designed to facilitate cross ventilation through the house, and admit daylight into the centre of the building.
Low occupancy wet areas including bathrooms and a laundry are located along the West side of the building. This maximises their exposure to ventilating breezes, and buffers the main body of the house from solar gains from evening sun.
The steps in the building plan also permit access to daylight for all rooms. The density of the development in the neighbourhood limits access to daylight from the West and East, so most rooms are designed to include a north or south facing window.
The main strategies were:
- To maximise airflow through the building
- To reduce summer solar gains to a minimum (without compromising daylighting)
-To insulate the roof and walls
Airflow
The house was designed to take advantage of the prevailing South-Easterly and North-Easterly winds. Louvres on each facade and concertina doors along the North facade allow the occupants to open the house to cooling breezes. The ground floor is open-planned with a central double height space to facilitate stack and cross ventilation. Louvred ventilation "towers" facing North and South are also used to promote airflow. Wet areas such as bathrooms, the laundry and the kitchen project from the house to capture breezes.
At the design phase flume testing was carried out to evaluate the performance of the building in NE and SE wind conditions. This involves placing a model of the building in a liquid and subjecting dyes to currents to assess flow patterns around the house. The results of these tests were used to optimise the size and location of openings. For example the size of the towers was reduced on the basis of the tests.
Solar Gains
The house is laid out to open it up to low incident radiation from the North and East, to allow the house to warm up in the morning and in winter. Service areas (the bathrooms, the laundry and circulation spaces) are used as buffer zones along the West side of the house, to reduce the impact of heat gains from low evening sun on the living spaces. The roof material selected is a light colour to reflect as much sunlight as possible from the roof and reduce solar gains.
Glazing
Glazing has been located to minimise uncontrollable solar gains, with west facing glazing eliminated altogether. The glazing was assessed using the GSL energy modelling programme, developed at the Queensland University of Technology. GSL is used to compare different types of glazing within a given window and building design. The modelling programme Radiance was used to evaluate interior lighting levels. Using these modelling tools, the design team selected a blue tinted glass with a low emittance coating. This reduces the heat gains to the house while maintaining a good level of daylight. The blue tinting is very subtle and does not detract from the outlook. South facing glazing (which is not exposed to direct sunlight) is clear, to reduce the cost of glazing.
Shades have been installed over the North facing windows, to reduce solar gains from high summer sun.
Insulation
Foil type insulation was selected for the walls as it is suited to the warm climate. The double layer of foil, which incorporates an air gap, reduces the transfer of heat from the sun through the walls. An R-value of 0.67 is achieved in the walls.
The roof is insulated with a combination of foil insulation and fibreglass insulation. These operate to reduce heat losses through the roof in winter, and solar gains in summer. An R-value of 2.6 is achieved in the roof.
The strategies employed to optimise indoor air quality included:
- High levels of passive ventilation
- Material selection and design
- Location of the carport
Passive Ventilation
As described in the building design section, the house makes use of passive ventilation strategies to maximise airflow through the building. Increasing the rate of air changes ensures that there is no build up of pathogens or toxins from the house or household operations.
Materials
Materials with low volatile emissions were selected wherever possible. Both interior and exterior timber work in the house are finished with locally sourced organic products, eliminating the need to use varnishes. The plasterboard walls are finished using a long life organic paint system, as standard paint products are associated with harmful off-gassing.
The use of reconstituted wood products, which contain glues (which can emit harmful fumes), has also been kept to minimum. These are used only in structural elements like the portal frames and floor joists. Instead solid timber has been used extensively in the house. The timber was locally sourced, and recycled where possible. Where suitable recycled timber could not be obtained, plantation was specified.
It was also decided to use HDPE waste water pipes and polypropylene water supply pipes, rather than PVC piping. Greenpeace have shown that the use of PVC involves production and transport of large amounts of toxic material and by-products (for more information see the Greenpeace website at: www.greenpeace.org). In use, PVC leeches toxins into water systems,and produces toxic fumes in a fire.
Planning
The carport was deliberately separated from the house, and designed to be open to the wind. This prevents harmful fumes from the car being drawn through the house.
The design strategies for reducing embodied energy in the building were to:
-Minimise site works
-Use recycled and local materials where possible
-Select low maintenance, long life materials and finishes
-Design the building structure for flexible planning and reuse
-Select materials and construction methods that facilitate reuse.
Site works
As discussed in the site planning section, the house was designed with mainly timber foundations to reduce the need for earthworks. Soil removed for construction was also retained on site, for redistribution on the site. This eliminated the transport energy required for disposal, as well as the impact of using the excess soil for offsite landfill.
Materials
Where possible, materials with low embodied energy were selected. For example locally supplied, recycled timber was used for floors, framing and most of the joinery. The timber was tested and certified for soundness by the supplier. This photo shows recycled joists. The concrete specified was a special low embodied energy product, which makes use of recycled cementing products, and recycled aggregate. Low maintenance, long life materials were also selected, to reduce the ongoing embodied energy consumption. For example, an interior paint system selected had a guaranteed life of 20 years.
Design for Flexible Planning and Reuse
The building utilises a series of glue laminated portal frames, which minimise the amount of bracing walls required, and thus increase the flexibility of the building. Internal partitions can be added or removed from any part of the house, without affecting structural integrity. The use of frames also allows the building to be open plan with large areas of windows and doors. This assists with the passive ventilation, heating and lighting strategies.
Materials and Detailing for Easy Reuse
The house makes extensive use of timber, which can be easily recycled in the event that the house is demolished.
The design strategies for reducing the operational energy of the house were to:
-Plan for passive heating and cooling
-Access natural light
-Use low energy lights and localised switching
-Specify energy efficient appliances
-Specify electric boosted solar hot water heating
-Install photovoltaic panels
Passive heating and cooling
As discussed in the climate section, the house has been planned and detailed to maintain a comfortable temperature, using passive heating and cooling. The main strategies are: planning for stack and cross ventilation, reducing midday and afternoon solar gains, and insulating the roof against heat gains and losses. The success of the natural ventilation strategy has elimnated the need for air conditioning, significantly reducing the total energy requirements of the house.
Natural light
Daylight levels within the house have been maximised, without admitting excessive solar gains. This was achieved by optimising the window size, selecting a glass type which maximises light transmission, and locating windows to control heat gains while maximising light admission (for more information see the climate section).
Lighting
Lighting in the house is predominantly long life, low energy fluorescent bulbs. This not only reduces the energy consumed by lighting, but also reduces the heat load within the house. The lighting design strategy was to localise switching as much as possible. This allows small areas to be lit, at any given time, further reducing the energy consumed by lighting.
Appliances
Some energy efficient appliances have been selected for use in the house. For more information about energy rated appliances see the Energy Rating website at: www.energyrating.gov.au.
Solar hot water
Hot water is supplied by an electricity boosted solar hot water system.
Photovoltaic Panels
A 1.44kW array of photovoltaic panels was installed in September 2000. The panels are connected to the local grid, so that surplus supply is exported (there is no need for batteries).
The water use reduction strategies included:
-Treatment and storage of rainwater for household use
-Treatment and storage of greywater for future garden use
-Selection of plant species suited to the area
-Installing an irrigation control system to reduce overwatering
Rainwater
Rainwater is collected from the roof and stored in tanks. The main tank is a 22,000 litre tank buried below the house, this is supplemented by a 1,000L galvanised tank. Water quality is protected by a twenty-micron filter and first flush devices, which divert the first 120 litres (8mm) of each downpour into the local stormwater system. The rainwater supply is supplemented by town supply. The local council required that there should be no connection between the town supply and the rainwater tank, and this was achieved by allowing for an air break between the tap from the town supply, and the maximum water level in the rainwater tank (yearly testing of a backflow preventer would have been prohibitively expensive). A water level sensor alerts the occupants when town supply is required. This monitoring system is to be replaced by a two level float valve, which will automatically import 1,000L of water when the tank reaches a specified low level.
Greywater
Greywater (water from basins, laundry and the showers) is collected and treated on site in a 6000L tank. Settlement and sand filtration are used to treat greywater before releasing it for reuse. The present legislation in Queensland prohibits the use of treatment of waste on site so the house is being used as a test case to assess the viability of this approach. The water would normally be used for the garden, but the local council are waiting for the results of the testing before they will permit the greywater to be reused on site. Because the site is served by the local sewerage system, regulations prohibited the treatment of blackwater on the site.
Plant species
Locally sourced native plants were selected, which would be suited to the local environment, and require minimal watering. The garden was designed according to permaculture principles, in order that it will eventually be self-sustaining. In the short-term, watering requirements were reduced by heavy mulching.
Irrigation monitoring devices
Two devices were installed to help monitor and minimise garden water use. The first is a tensiometer, which measures the dryness of the soil, and indicates when watering is required. The second is a Full Stop Device, developed by CSIRO. This sends a signal to the householder when water has reached the bottom level of the roots of the plants.