A simple, energy efficient family home
Mooroopna Home 2023 J.MAR Constructions Smart design choices and attention to detail during construction ensure this modest family home is cost-effective and better for the environment. By focussing on energy efficiency early in the design process, you can significantly reduce the cost of complying with a 7 star minimum, improve quality, and ensure it’s more comfortable to live in year-round. This home demonstrates that achieving a 7 star energy rating is attainable with current design approaches and technologies, highlighting both the health and comfort benefits of site responsive home design.
While it may look like your average new home built from standard materials, thanks to some smart design choices this home, built by J.MAR Constructions as part of the Sustainability Victoria 7 Star Homes Program, is more comfortable to live in. It's 73% cheaper to run than the same home if built to the 6 star NatHERS minimum.
“We just wanted to showcase how easy it is to design and build an energy efficient home. Cost effective inclusions such as electric appliances, double glazed windows, a solar PV system and of course the correct response to orientation were all it took to build such a well performing home.”
This feature home article unpacks the key design choices made to ensure this comfortable family home could achieve its 7 star + NatHERS rating, highlighting the bill savings associated with the homeowner's choice to build all-electric.
Feature home snapshot
Builder: J.MAR Constructions Pty Ltd trading as Solar City Eco Homes
Designer: HDN Building Design
Location: Mooroopna Victoria - NatHERS Climate Zone 66
Description: Single Storey, 3 Bedroom 2 Bathroom
Size: Dwelling: 145.8m², Garage: 40.36m² and Alfresco: 19.27 m²
NatHERS energy rating: 7.5 stars*
Whole-of-home: All Electric: Heat pump hot water, efficient reverse cycle heating/cooling, induction cooking, energy efficient lighting Solar PV
Other features: 2000L Rainwater tank
Total build cost (excluding land): $400,000 including Solar PV ($1890 per m2)
*This home has been rated using FirstRate5 5.3.2b under NCC2019.
Energy and cost savings
Using Sustainability Victoria’s Whole of Home Pilot Tool, the estimated annual energy use, emissions and energy bill amounts were calculated for this home and compared to the same home built to the current minimum requirements under NCC2019, 6 stars with average mixed fuel appliances without solar PV. Thanks to the 7.5 star NatHERS rating and the selection of all-electric appliances with Solar PV the new owners of this home are expected to save $1,373 annually on their utility bills. This home exports more energy generated on site solar PV than it consumes from the grid, resulting in negative energy use and -4.13 tonnes of CO2-e emitted each year.
| Mooroopna House, if it were a mixed fuel 6 star home without solar PV | Mooroopna House (actual – 7.5 star all-electric home with solar PV) | Savings [%] | |
|---|---|---|---|
| Annual energy use | 20,357 MJ | -14,805 MJ | 173% |
| tCO2-e emitted per annum | 5.06 | -4.13 | 182% |
| Annual energy bill | $1,892 | $519 | 73% |
Table 1: Predicted annual energy use, emissions and costs, including supply charge for Mooroopna House under a business as usual and as built scenario.
North facing living room soaked in winter sun. 2023 J.MAR Constructions 7 Star upgrade and appliance details
| Feature | Standard 6 star home design in the same climate zone | Mooroopna House |
|---|---|---|
| NatHERS rating | 6 stars | 7.5 stars |
| Design orientation | North-facing | North-facing |
| Insulation - ceiling | R3.5 batts to ceiling | R6 batts to ceiling |
| Insulation - external walls | R2.0 to external walls | R2.7 to external walls. Additional R1.1 Rigid foam insulation to western walls. |
| Insulation - internal walls | No insulation for internal walls | R2.5 to all internal wet area walls (all interior walls insulated for acoustic benefit) |
| Windows | Single glazed aluminium | Double glazed aluminium |
| Hot water | Solar hot water system - gas boosted | Heat pump hot water |
| Rooftop Solar PV | Not applicable | 6 kW Solar PV system |
| Heating and cooling | Gas ducted heating and no cooling | 2 x Split system air conditioners |
| Lighting | Maximum 5 W/m2 | 2 W/m2; energy-efficient LED lighting |
Mooroopna Home plan J.MAR Constructions and HDN Building Design Home design
Located on a small suburban block in a new subdivision, this home demonstrates that efficiency can be the new normal. Built using conventional techniques and standard materials, the design is intended to feel comfortable all year round, with minimal reliance on heating and cooling. By working with the client from early in the design process J.MAR Constructions has been able to guide decision making and come up with a simple, affordable, and well performing home.
“Often our clients aren’t aware of how their design choices impact the performance, comfort, and quality of light in their new home… Our focus is on first understanding the customers wants and needs and then to recommend the best orientation, ideal location and size of windows and appropriate appliance selections,”
Some of the key decisions involved in this home achieving its NatHERS rating are outlined below:
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This home achieved a higher star rating by paying attention to orientation and making the following design choices:
- Locating the main living spaces to the north.
- Including appropriately sized eaves to shade north facing glazing from the hot summer sun while allowing lower angle winter sun to enter and warm the house. Eave depth is varied along the northern wall, with deeper eaves protecting the glass doors and floor to ceiling windows in the main living area.
- Locating the garage on the southern side of block to enable more habitable rooms on the north.
- Locating the undercover alfresco to the west side of the main living space and including a full height screen on the west side to protect it and the west facing glazed doors from the western sun. Eaves extend out over the alfresco on the north increasing its functionality by ensuring it is fully shaded in summer but soaked in sun in winter.
- Minimised western glazing, including locating the bedroom 2 window on the southern wall to avoid excessive overheating.
- Additional insulation to the western wall to prevent thermal bridging (not required to achieve 7 stars).
Rotating this home’s floorplan returns a range of possible NatHERS ratings between 7.0 stars in its worst and 7.5 in its best orientation, showing the simplicity and efficiency of this floor plan. Although this home would achieve 7 stars in its worst orientation, to take advantage of the winter sun, having the living spaces to the north will keep these rooms warm, light and bright.
No matter the orientation of the block there are strategies to ensure each home is optimised to make the most of site conditions.
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To achieve 6 stars, this home only requires single glazing. By upgrading insulation and specifying double-glazing to the main living room windows and sliding doors, this home can achieve 7.1 stars.
To achieve its 7.5 star rating, double glazing with standard aluminum frames was specified throughout.Windows are the weakest aspect of a home’s thermal envelope, up to 40% of a home’s heating energy can be lost and up to 87% of its heat gained through windows. While the quality of the glass and frames are important factors when it comes to a home’s performance; the size, orientation and shading of glazed areas have a big impact on a home’s efficiency.
Some of the strategies employed in this home to optimize its glazing are:
- Locating main living space windows along the northern wall and including appropriately sized eaves.
- Inclusion of vertical shading to protect western glazing.
- Choice to locate bedroom 2 window to the south instead of the west to protect it from overheating in summer.
Inclusion of a north facing high-level window in the master bedroom to take advantage of the northern sun. A high-level window enables the bed to sit against this wall and reduces the window to wall ratio. While a larger window on the northern wall would be preferable, the design of this home requires a large window on the eastern (font) façade.
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To achieve a 6 star NatHERS rating, this home requires R2 insulation in external walls and R3.5 insulation in the ceiling.
To upgrade the home to 7 stars the following insulation upgrades were required:- Wall insulation has been upgraded to R2.7.
- Ceiling insulation has been upgraded to R6.0.
- Internal walls have been insulated with R2.5 bats which has thermal performance benefits when located between conditioned and unconditioned zones and acoustic benefits throughout.
- R1.1 rigid foam insulation has been added to the slab edge and to the western wall. The rigid foam insulation along the western wall reduces thermal bridging of the timber stud frame, improving overall performance of this wall. However, it is not required to achieve a 7 star rating.
Adding insulation to internal walls and to floors between levels is a smart choice and will have ongoing occupant health and comfort benefits due to improved soundproofing particularly in a smaller family home like this one.
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The use of cavity sliding doors in this home enables the owners to zone the space and avoid unnecessarily heating areas such as hallways. Smart zoning can significantly reduce the cost of heating and cooling a home and increase occupant comfort. Zoning has additional acoustic benefits allowing for more flexible use of your home. Standard installation of cavity sliding doors results in a major source of drafts in a home. Care should be taken to ensure good air tightness by sealing the frame surrounding the door assembly to the plaster, a quality detail to prevent draughts.
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The choice to include efficient all-electric appliances and solar PV ensures this home not only meets but exceeds the Whole-of-Home energy requirements set to be introduced with NCC2022. The residents of this family home will be saving 73% or approximately $1370 annually on their energy bills compared to if they built this home to the current minimum 6-star standard.
- Thanks to its efficient thermal envelope and smart zoning, instead of a gas ducted heating system this home’s heating needs can be met with two split system air-conditioners. Split system air conditioners are the most efficient way to heat and cool a home.
- Each bedroom, the main living space and the alfresco area in this home is fitted with a ceiling fan. Ceiling fans help with natural ventilation and reduce the need for additional heating and cooling, boosting thermal comfort in the home. The inclusion of ceiling fans in this home increases the NatHERS rating by 0.1 star.
Heat pump hot water enables the residents to maximise on-site consumption of solar. It also frees up roof space for solar panels by removing the solar collector required for gas boosted solar hot water which is the most common hot water option used in Victoria today. The inclusion of a rainwater tank plumbed to the toilets enables the use of heat pump hot water and saves the use of potable water in the home.
Mooroopna Home Kitchen, showing induction cooking and cavity slider doors used for zoning Home construction
Having a well thought out design is essential to achieving a cost-effective energy efficient home. However, once the design is locked in and the home is under construction, it is crucial that the builder takes care to ensure the home meets its intended design outcomes. The construction process for this home involved some additional steps ensuring quality outcomes in the build:
- The builder focused on additional care when installing insulation, ensuring coverage is continuous and free from gaps. This includes around windows, external corners and wall junctions which are commonly missed.
- The builder employed a plaster airtightness strategy which includes caulking of plaster to the concrete slab, caulking service penetrations and caulking and sealing around cavity slider doors.
All exhaust fans and the kitchen rangehood are fitted with in-line dampers and are vented externally under the eaves. This prevents draughts and reduces issues with condensation associated with extraction fans venting into the roof cavity.
As built verification
Sustainability Victoria engaged an independent as-built verification assessor to ensure that the home was built to meet its intended energy efficiency targets. The verification check included a blower door test to measure air leakage, a thermography test to check insulation coverage and visual inspections of glazing, ceiling insulation, extraction fan vents and appliances.
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The home was blower-door tested to determine the air leakage rate. The home passed the blower door test with an air-permeability of 6.41 m3/h/m2 @ 50Pa, which is good result and well below the requirements of the National Construction Code.
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This test uses a thermal imaging camera that can ‘see’ heat, enabling the assessor to inspect the installation of insulation, by looking for hot spots and cold spots in the ceilings and walls. The inspection is passed if no more than 5% of insulation is missing in the walls, floors and ceilings.
The home passed with only a 0.42% deficit in ceiling insulation coverage and an impressive 0% deficit in the walls.
Outcomes
The design of this home achieves 7 stars in all orientations; however, it is optimised for its site, achieving 7.5 stars with north facing living areas and well-designed eaves. This impressive result has been possible on a small block with standard construction techniques and materials and a typical home design, demonstrating that a site responsive approach ensures a home can comply with and exceed the updated 7 star requirements and still deliver an affordable outcome for the homeowner.