Off-grid house at Gundaroo, NSW

The facts, figures and story of going off-grid at Gundaroo - a guest post by Sue Ogilvy and Danny O'Brien - thanks!


Inviting outside dining area

Inviting outside dining area

Hi Michael,

We thought we might like to let you know how influential you have been in advancing sustainability.

We first read your work about Sustainable House in 2009 and that, along with The Natural Step and some permaculture influences flung us into a new orbit. Since then, we’ve taken up new careers and lifestyles – I’m developing and applying accounting standards for ecosystems in agriculture and in the national accounts, we have a social enterprise that retails healthy, ethical, sustainable meat into Canberra, Danny is Treasurer of Canberra City Farm and we have 100ha in Gundaroo where we have just completed our house. Our house is inspired by all your work as well as great engineering from overseas. In order to minimise our need for energy to heat the house during Canberra winters, when solar energy is in (relatively) short supply, we decided to build to PassivHaus standard. In other words, we’ve built a house in Canberra with NO heater….. and we’re not mad.

I’m very pleased to be able to report that, despite cold miserable days, the coldest temperature we’ve recorded in the house is 19.2 degrees. It’s just wonderful to be comfortable and not feel guilty about it!

Our PassivHaus project

The design and construction brief was clear – design and build a home that is based on passive-solar design, constructed of natural materials where possible, minimise the chemical toxicity of the building materials, and leverage appropriate levels of technology to reduce the ongoing operational costs for heating, cooling, power and water.

The solution to the brief has been to build a simple but elegant home using German PassivHaus principles, with power supplied from an off-grid 9kW Solar system.

The PassivHaus standard builds on regular passive solar design principles, and requires increased performance standards for insulation, air leakage control, and management of energy required to heat and cool the home. (See notes below.)

We’ve been in the house for 2 months now, and through warm sunny days, gloomy days and overnight temperatures of -6oC, the house has really shown that it is delivering on the promise. The temperature has not dropped below 19.2 degrees (even with the freezing nights) and has stabilised at a comfortable 21-23 oC during gloomy days and cool nights. The higher temperatures due to the solar gain on sunny days are easily managed through opening the clerestory windows in the living room and tilting other windows throughout the house to manage a very comfortable temperature.

Located on a 250acre property in Gundaroo (near Canberra), it was straight forward to orient the home true North in order to maximise solar gain during winter. This ensures maximisation of heat gain during the cold winter months that are experienced in the area.

Thermal mass is provided through the use of a polished concrete floor. The slab construction is a floating raft slab, which has been fully insulated using 50mm XPS foam (R1.74) in order to ensure there are no thermal bridges between the slab and the ground.

The walls have been constructed using a 140mm stud wall (allowing for high levels of insulation @ R4), and are covered with two membranes:

-        The external membrane provides a water resistant, breathable membrane that effectively acts like a Gore-tex cover for the house – providing a moisture barrier for the frame, whilst allowing any moisture in the frame to pass to the external environment.

-       The internal membrane provides a humidity variable vapour redarder and airtight membrane, allowing moisture to pass from the frame to the interior of the house whilst providing an air tight seal to stop any movement of air.

The combination of the two membranes provides an air tight seal for the house, whist at the same time ensuring maximum longevity of the structural frames through ensuring no moisture is held in the frame cavity.

Similar construction techniques were used for the roof/ceiling structure, achieving R7 insulation throughout the whole house. A false ceiling was used throughout the house to allow for the installation of downlights to ensure there were no requirements to have breaks in the layers of insulation.

Temperature control, air tightness, and thermal gain is further managed through the use of triple-glazed timber/aluminium windows, utilising tilt-turn mechanisms to provide an air tight seal when closed, whilst enabling dual modes of operation – tilted to allow low levels of air to circulate through the house during winter; turned (and opened) to allow the house to be flushed with cooler air during summer evenings and nights.

The quality and effectiveness of the construction has been tested by an independent building airtightness (blower door test). The house achieved a rating of 0.47 Air Changes per Hour @ 50 Pa, easily meeting the the 0.6 ACH required for PassivHaus standard, and an order of magnitude better than standard houses that typically operate between 10 to 20 ACH.

The timber/aluminium combination was chosen to allow the use of natural materials (timber interior) whilst at the same time minimising maintenance and wear (aluminium exterior). The timber frame ensures that there is no thermal bridge.

Air quality is controlled through the use of a heat recovery ventilation unit. The ventilation design for the house unit takes stale air from within the house (from the wet areas and kitchen) and replaces that with fresh air from outside (into the living areas and bedrooms). The unit utilises a rotating drum design that operates at 80% efficiency, ensuring that heat is retained within the house during winter and is kept out of the house during summer. The advantage of the rotating drum technology is that humidity levels are maintained within the house at a comfortable level. The ventilation unit can also be placed in summer bypass mode in order to flush the house with cool air at night.

Further protection during the warmer months has been achieved through the intelligent placement of the eaves (960mm on the North), combined with the deep pergola that will support the deciduous grape vines for a lush, cooling aspect on the North and East sides of the house. The carport on the Western aspect protects the house from the worst of the Westerly sun.

The whole system has been designed to operate off-grid, utilising power from a 9kW off-grid solar system which has an 1800AH/48V battery backup system. The solar system has been implemented using 3 strings of panels (12 panels each) at varying levels of inclination (40, 25 and 20 degrees) ensuring that power is evenly provided throughout all months of the year.

In order to minimise the load on the system, the lighting throughout the house is based on LED technologies. 

The system is rounded out with a Sanden Eco Hot water heat pump system. Operating from the renewable energy source, the heat pump system ensures that the only fossil-fuel required for the home is used for the gas cook-top and oven (we considered the load on the solar to be too high to allow for electric cook-top and oven).

Water Efficiency

Being located in rural NSW, the house is naturally off-grid for water, with a 115kL tank installed that catches rainwater from both the house and shed.

Low-flow taps and shower heads have been installed to ensure that water is conserved during the drier months.

The waste water from the house is processed via the worm-farm composting system, with the processed water being pumped to a dispersal trench adjacent to the planned orchard. This allows us to minimise the additional water required for growing of our food.

Other septic systems were considered during the process that may have allowed other uses of the processed water, but they were either too high energy users (pumps running full time) or were not appropriate for the soil types in our area.

Water for the garden and food production areas will come from a combination of a local bore and rainwater.

Indoor Air Quality

Maximising indoor air quality has been central to the design.

Starting with the use low VOC paints and natural timber and concrete sealers and oils, the internal air quality is maintained through the use of the active ventilation system. Fresh air is constantly fed into the house via the heat recovery ventilation unit, whilst at the same time maintaining a very comfortable living temperature without the need for any active heating.

The original plan for the cabinetry was to use ply doors due to the perceived lower VOC content of ply versus MDF and chipboard. However, once it was identified that low VOC could be achieved in the manufactured materials for the cabinetry through the selection of SuperE0 MDF, the overall chemical load of the house was reduced, with SuperE0 interior for the Laminex finishes part of the build.

Material Selection, Resource Efficiency, Site Management

The key criteria and solutions for material selection were:

-        Sourced from sustainable, renewable sources:

o   LVL timber used for construction of the frame and roof

o   Timber used in the window frames

o   Timber used in the pergola (regrowth Red Ironbark)

o   Woolen carpets

-        Materials made from recycled material:

o   Aluminium exterior to the windows

o   Benchtops and feature timber throughout from recycled Blackbutt

o   Insulation made from recycled glass

o   Recycled materials used in construction of the manufactured board for the cabinetry

-        Materials made from materials that could be recycled:

o   Zincalume and Colourbond cladding

o   All the timber components

-        Materials sourced locally:

o   Site fill sourced from clay located on the property (thus reducing energy required for haulage)

Whilst we were aware of the embedded energy contained within materials such as the concrete floor, our analysis showed that the benefits achieved through the use of thermal mass would by far outweigh the energy used to produce the product.


The house is located on a slight ridge sitting above a drainage line that has the potential to carry water during extreme conditions (taking water from the overflow of a neighbour’s dam). A deliberate design decision was made to not cut the house site into the hill, but rather to use the local clay as fill for the site in order to raise the house pad above any drainage lines. An earthen berm was constructed using surplus fill on the Northern, Eastern and Southern boundaries of the house site to further control any storm water. Using the berm to slow the water as it moves through the landscape allows the water to soak into the sub-soil rather than flowing (and potentially causing erosion).


Monitoring performance

One of the major frustrations when designing the performance of the home was the lack of real data relating to key decision points for the build (e.g. do we fully insulate the slab to limit heat gain during winter, or do we just edge insulate in order to bleed heat during summer?).

As a consequence, we have run conduit through and under the slab in order to provide temperature monitoring points in the following locations:

-        In the ground under the slab (below the insulation)

-        Outside the house in the ground (as a comparison to the under-slab temperature)

-        In the slab on the Northern half of the slab

-        In the slab on the Southern half of the slab (to see how long it takes for temperature normalisation throughout the slab)

In addition to thermocouple sensors in those points, we are in the process of implementing a monitoring solution that links to the MODBUS interfaces for the Solar system (to monitor energy production and use) as well as the Ventilation unit (to monitor temp in and out – and therefore the effectiveness of the ventilation system).

Fitting into the environment

The design has taken cues from the rural environment in which the house belongs. From utilising zincalume as the external finish to reflect the range and variety of sheds and water tanks in the area, to using intelligent selection of colours internally to pick out hints of the broader vegetation as the seasons change, this home has been designed to sit comfortably in the landscape.

Notes: Background info re PassivHaus standard

Specifically, the standard requires the following (Ref:

1. The Space Heating Energy Demand is not to exceed 15 kWh per square meter of net living space (treated floor area) per year or 10 W per square meter peak demand.

In climates where active cooling is needed, the Space Cooling Energy Demand requirement roughly matches the heat demand requirements above, with a slight additional allowance for dehumidification.

2. The Primary Energy Demand, the total energy to be used for all domestic applications (heating, hot water and domestic electricity) must not exceed 120 kWh per square meter of treated floor area per year.

3. In terms of Airtightness, a maximum of 0.6 air changes per hour at 50 Pascals pressure (ACH50), as verified with an onsite pressure test (in both pressurized and depressurized states).

4. Thermal comfort must be met for all living areas during winter as well as in summer, with not more than 10 % of the hours in a given year over 25 °C.



Sue and Danny run a farming business and it's worth taking this link to see more information about them and whether their site has something to offer you.

Here are the contact details for some of the project team:


Paul Howick

Licenced Builder

F: 02 6259 2985

M: 0408 624 593

PO Box 246, KippaxACT2615

PassivHaus technology:  

Windows, Ventilation unit planning/design and supply, Heat pump hot water system, along with plenty of advice in relation to the overall planning and design for the house came from Laros Technologies: 

Andreas Luzzi

LAROS Technologies

Address:  Unit 2, 5 Bodalla Place, Fyshwick ACT 2609, AUSTRALIA

Phone   +61 (0)2 6160 7777

Solar Setup: 

Tim Davaris from YGrene Energy was absolutely fantastic, consultative, and was very competitive price wise with a high quality solution

Tim Davaris

Ygrene Energy Pty Ltd

PO Box 12 YASS NSW 2582        0419 267 042