Building a Zero Net Carbon Home for efficiency and affordability
Challenges
- Choosing the right mix of energy efficient features, that meet the Zero Net Carbon Homes specification ‘at an attractive price point for home buyers’.
- Finding the right levers to effectively market and sell the home when the sustainability angle didn’t resonate with home buyers as much as promoting cost savings.
Home snapshot
Name of the home: Z-Range
Estate: Timbertop Estate
Address: 290 Newark Place, Officer
Design: The Zenith 274
Retail pack: Eco Saver
Home Builder: SJD Homes
Land Developer: Parklea Developments
Size: 255m2
Retail cost: $246,000 including Eco Saver package
Savings
Estimated annual savings: $2,210
Estimated cost to consumer: $10,000
Payback period for package upgrade: 4.5 years, based on cost to consumer
Estimated annual greenhouse gas savings: 100% or 8tCO2-e
| 290 Newark Place, Officer, if it were a 6 star home | 290 Newark Place, Officer (ZNC) | Savings (%) | |
|---|---|---|---|
| Energy use | 10,878kWh | -53.6kWh | 100% |
| tCO2-e emitted | 8.1tCO2-e | 0tCO2-e | 100% |
| Annual energy bill | $2865 | $655 | 77% |
Table 1: Annual energy and carbon emissions savings of 290 Newark Place (ZNC home)
Ratings
NatHERS rating: 6.9 Stars
Residential Efficiency Scorecard: 10 stars
Carbon status: zero net carbon
Introduction
The SJD Homes Z-Range display home in Officer, Victoria was designed to run exclusively on electricity, with energy consumption fully offset by renewable energy generated on-site. It was the first display home launched as part of Sustainability Victoria on behalf of the Victorian Government’s Zero Net Carbon Homes pilot program.
The main challenge involved choosing the right mix of energy efficient features to meet the Zero Net Carbon Homes program specification and offer the home at an attractive price point for buyers. Choosing the right marketing and sales messaging also played a part in how buyers responded.
SJD Homes is a medium-sized residential home builder operating in Melbourne’s south-eastern corridor. Director Simon Dunstan has been a strong advocate for energy efficient building design for many years and first offered a sustainable home to buyers in 2009. “The market wasn’t quite ready at that stage for low carbon home design,” Simon recalls.
Consumers are now more aware of the benefits – like year-round comfort and lower energy bills – so demand for low-carbon dwellings is beginning to take off.
Home design
The design for the SJD Homes Z-Range home was created in collaboration with Dr Josh Byrne from Curtin University, CSIRO, SECCCA, Parklea Developments and Sustainability Victoria. The aim was to create an affordable zero-emissions home.
Upon joining the Zero Net Carbon Homes program in late 2018, SJD Homes measured their Z-Range home against our program’s specification by using a purpose-built design modelling tool. They were then able to finesse their packaged features for the home buyers’ market.
The Z-Range display home located in the Parklea development, Timbertop estate in Officer, features the SJD Homes’ The Zenith 274 design.
The 255 square-metre home includes four bedrooms, two bathrooms and two living areas and is the perfect home for a family of four. The retail price of the display home is $246,000; well below the average cost of a new home of the same size, which is approximately $316,000 (or $1270.80 per sqm according to the Australian Bureau of Statistics). This price point meets SJD’s aim to offer a sustainable product that’s affordable for home buyers.
The display home achieved a 6.9 stars NatHERS rating, which is 0.9 stars above the National Construction Code’s minimum star rating for new homes. This makes the home cheaper to run as well as more comfortable to live in.
Interior of the home The home has been built to higher energy efficiency standards than the National Construction Code (NCC) requires. It features northern orientation of living areas, air tightness, LED lighting, energy efficient fixed appliances and a battery ready roof solar PV system.
The building shell design includes:
- north-facing living areas to harness daylight and heat in winter
- eaves shading to protect against solar heat gain in summer on the north side
- a light-coloured Colorbond roof to reflect the sun’s heat
- doubled glazed, thermally-broken windows to maintain a comfortable internal temperature
- wall and roof insulation with a high R value that maximises thermal comfort and keeps energy costs down.
The fixed appliances include:
- a Sanden heat pump hot water system with a COP of 5.06
- a Braemar KSHV71D1S 7.1kW 3 star split system for the heating and cooling (in the family and living areas
- a Braemar MSHV11 11.4kW multi-head split system for heating (ACOP 3.8) and cooling (AEER 3.2) the rest of the house
- an electric induction cooktop.
Comparing energy ratings with a standard home
A current standard new home design won’t necessarily have energy efficiency features that save money and reduce emissions.
All new homes in Australia are required to achieve a 6 star NatHERS energy rating under the NCC. However, a home built to the Zero Net Carbon Homes specification requires a minimum 6.5 star NatHERS energy rating. This display home meets the Zero Net Carbon Home standard and has a 6.9 NatHERS energy rating.
| NatHERS energy rating | Rating |
|---|---|
| Industry standard | 6.0 stars |
| Zero Net Carbon Homes minimum requirement | 6.5 stars |
| SJD Homes Z-Range display home | 6.9 stars |
When the SJD Homes zero net carbon home design is compared to the standard The Zenith 274 home design, the benefits include superior build quality, increased comfort, smaller environmental footprint and reduced energy costs.
Comparing design features with a standard home
The table below compares the SJD Homes zero net carbon home design with a standard fully electric home design.
| Feature | Standard home design in Climate Zone 6 | 290 Newark Place, Officer home design |
|---|---|---|
| Design orientation | Variable | North-facing |
| Insulation | R3.5 batts to ceiling | R5.0 batts to ceiling |
| Insulation | R2.0 external walls | R2.5 to external walls |
| Insulation | None (sound proofing only) | R2.5 to internal walls of wet areas |
| Insulation | R1.0 ductwork | R1.5 ductwork |
| Sarking | Foil sarking only | R1.3 60mm Anticon blanket in the roof |
| Sarking | Wrap to external walls | Wrap to external walls |
| Windows | Single glazed aluminium, not thermally broken | Thermally broken double-glazed windows |
| Hot water | Any compliant product on the Australian Market | Sanden heat pump with a COP of 5.96 |
| Roof-top solar PV | Not required | 5kW battery-ready PV system with 17 solar panels |
| Air-tightness | 10m3/hour m2 at 50Pa (not verified) | 4.63m3/hour m2 at 50Pa (verified) |
| Heating and cooling | Any compliant product on the Australian Market | 8kW reverse cycle multi-split system with a 3 star rating for heating and cooling |
| Heating and cooling | Any compliant product on the Australian Market | Multi-head ducted reverse cycle 11.4kW system with ACOP 3.8 and AEER 3.2 |
| Kitchen | Any compliant product on the Australian Market | Induction cooktop |
| Kitchen | Any compliant product on the Australian Market | Premium energy efficient kitchen appliances |
| Lighting | 5W/m2 | 1.6W/m2. Energy efficient LED lighting IC4 rated |
Benefits of the design
Lower energy bills
SJD Homes’ zero net carbon home is designed to save money on power bills through:
- a north-facing orientation
- 95% insulation coverage with a U value of 5 for the ceiling insulation and 2.5 for the wall insulation, as well as additional draught proofing
- double glazing for all windows and sliding doors
- energy efficient fixed appliances, including heating and cooling split systems and heat pump hot water
- a 5kW solar PV battery-ready system on the roof.
These measures lower electricity and gas consumption thereby lowering energy bills by up to 78%.
Savings
Passive design, energy efficiency features and solar PV will lower energy bills by more than 50% compared with a standard new home.
Comfort and health
Standard homes with a 6 Star NatHERS energy rating, insulation meeting only basic NCC requirements, no double glazing and no post construction as-built verification testing, are often colder in winter, hotter in summer, noisier, more draughty and more likely to allow dust and pollen into the home, making these homes much less comfortable and healthy to live in.
By comparison, the indoor ‘feel’, temperature/conditions of 290 Newark Place is comfortable no matter what the weather conditions outside the house. Modelling data also shows that the home, if left unheated and cooled would have less hours outside the comfort range between 18–26°C.
Comfort – higher levels of insulation, draught-sealing and double glazing of windows and doors reduce both air flow and heat/cool into and out of the home and maintains a stable indoor temperature. This makes the home warm and cosy in winter and pleasantly cool in summer. Double glazing also keeps out unwanted external sounds.
Health – a tighter building shell reduces the introduction of dust and pollen from outside into the home and this can reduce the incidence of allergies and asthma. Air quality at 290 Newark Place is superior to many new homes built to minimum NCC standards. Building sealing techniques tighten the home’s shell, reducing the ingress of particulates including dust and pollen, which makes the internal air cleaner and less likely to cause distress.
Environmentally friendly
All the environmental design features including building orientation, the use of energy efficient appliances, draught-sealing, insulation and double-glazing, lower greenhouse gas emissions compared with a standard home. The addition of electricity generated from solar PV cells on the home’s roof off-set remaining greenhouse gas emissions, making this home one of a very small number of carbon neutral homes in Australia today.
Environmental footprint comparison
Standard home: 8tCO2-e per year
290 Newark Place, Officer: 0tCO2-e per year
The build
SJD Homes’ Z-Range display home in Officer was constructed over a six-month period.
Care was taken in construction of the building shell to produce a high level of air tightness, so that occupants are less reliant on using energy for heating and cooling, which accounts of up to 60% of home energy use.
To produce high levels of air tightness, extra care in installing the increased U- level insulation was taken to minimise air leakage, in particular around the window frames. Additional insulation was installed in the roof with both ceiling insulation and an anticon blanket cover. Silicone sealing between the slab and frame was applied and a sisalation wrap with an R value of 1.3 was installed with care taken to minimise tears and gaps. Additionally, draught sealed exhaust fans and weather strips were installed for further draught proofing.
As-built verification assessment
To verify that the SJD Homes Z-Range display home met the Zero Net Carbon Homes standard, an independent as-built verification check was undertaken to ensure that the original design intent had been realised in the build.
This verification check included two checks:
-
The home was blower-door tested to determine that the air leakage rate complies with the Zero Net Carbon Homes program standard of not more than six air changes per hour. The home passed the blower door test with an air-tightness of 4.63 air changes per hour. The standard requires a rate of between three to six air changes per hour. If the home falls below three, mechanical fan ventilation is required to ensure adequate fresh is available to occupants.
Acceptable range: Between 3.0 and 6.0 air changes per hour
SJD Homes Z-Range display home: 4.63 air changes per hour -
This test uses a special camera that can ‘see’ through the home’s interior walls to check that the insulation behind the walls and ceilings has been correctly installed and that no more than five per cent of insulation is missing. The display home passed this component of as-built verification if insulation coverage achieves greater than 95% coverage.
Zero Net Carbon Home maximum allowed: 5% missing insulation
SJD Homes Z-Range display home: 5% missing insulation
Sales and marketing
When SJD Homes’ Z-Range display home launched in October 2018, the zero net energy retail package was priced at $20,000 and the sales pitch centred around sustainability messages rather than the tangible benefit of cost savings. Sales of the Z-Range were initially low.
After remodelling the home design using the Zero Net Carbon Homes design modelling tool, reducing the cost of the sustainability features to buyers by absorbing some of the costs and Sustainability Victoria contributions, SJD Homes was able to reduce the package price to $4900.
Additionally, through customer journey mapping workshops and Sustainability Victoria’s consumer research, marketing and sales efforts focused on buyer benefits of cost savings in energy bills and lifestyle benefits of comfort and well-being.
These changes appealed to the market and, in June 2019, 27 homes were sold.
“Our new Z-Range design and Eco Saver retail package hits the mark with the buyer,” said SJD Sales Manager Rod Fitzsimmons. “Buyers can see the value of a small investment going a long way, for a healthier, more comfortable lifestyle, as well as ongoing savings in power bills.”
Conclusions
Buyers are becoming more conscious of the benefits of buying a sustainably designed and built homes for increased comfort and value. 290 Newark Place demonstrates superior passive design and air-tightness, uses energy efficient appliances to reduce energy use and generates on-site renewable energy to offset operational emissions. The home has also been independently verified to ensure that the final construction meets the design intent and the specifications of the zero net carbon homes program, thereby surpassing the current NCC requirements and delivering a superior product.
SJD Homes continues to sell the Eco Saver package outside of the Victorian Zero Net Carbon Homes pilot program. Due to the current price sensitive market, the As Built Verification assessment is offered to buyers as an optional extra.
As of November 2019, an additional 24 homes with the Eco Saver pack have been sold. The SJD Homes Z-Range display home in Officer was recently announced the national winner of the Display Home category in the 2019 HIA Australian GreenSmart Awards.