Energy-efficient and sustainable prefabricated homes
Ecoliv’s home in Yea with views over the valley (copyright Ecoliv). Prefabricated or ‘prefab’ homes are a growing portion of new home construction as they provide options for sustainable and cost-effective production, within a reduced time frame. Adding to their efficiency, Prefab homes are easily able to achieve 7 stars with their factory-based approach to construction creating an ideal environment for good levels of insulation and design optimisation. Prefabricated approaches typically fall into 2 main construction categories – modular and panelised – but within these is a huge range of different products on offer.
As part of Sustainability Victoria’s 7 Star Homes Program Ecoliv delivered 4 sustainable prefab modular homes. These homes are energy-efficient, achieving a star range from 7.0 to 7.7, through good levels of insulation, the inclusion of double glazing and solar passive design.
Feature home snapshot
Builder: Ecoliv
Location: Yea, Buffalo, Birragurra and Eaglehawk, Victoria
Design: EcoLiving and EcoGeneration ranges
Description: Single storey 2 to 4 bedroom dwellings
Size of homes: Range from 99.65m2 to 168.89m2
NatHERS energy rating: 7.0 – 7.7 stars*
Whole-of-home: Heat pump hot water, efficient heating/cooling and energy efficient lighting
Other features:
Solar PV and battery storage
10,000Lt rainwater storage**
*This home has been rated using FirstRate5 5.3.2b under NCC 2019.
**Ecoliv tailor water storage solutions to meet off-grid and CFA requirements
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 the 4 homes that Ecoliv built as part of the 7 Star Homes Program.
| Yea home | Buffalo home | Birregurra home | Eaglehawk home | |
|---|---|---|---|---|
| Annual energy use | -7250 MJ | -26,269 MJ | 19,922 MJ | -1,585 MJ |
| tCO2-e emitted p.a. | -6.06 tCO2-e | -7.33 tCO2-e | 3.5 tCO2-e | -0.44 tCO2-e |
| Annual energy bill | $297 | -$141* | $1,298* | $615* |
Table 1: Annual energy and carbon emissions savings of the Ecoliv 7 Star Program homes (*these homes were modelled without any heating/cooling appliances).
Living areas with views over the valley, Yea home (copyright Ecoliv). Home features
| Feature | Standard 6-star home design in the same climate zone | Yea home |
|---|---|---|
| NatHERS rating | 6 stars | 7.1 stars |
| Design orientation | North-facing | West-facing to capture the views over the valley |
| Insulation - ceiling | R3.5 batts to ceiling | R6 batts to ceiling |
| Insulation - external walls | R2.0 to external walls | R2.7 to external walls |
| Insulation - internal walls | No insulation for internal walls | R2.5 to all internal wet area walls |
| Insulation – floor | Uninsulated concrete slab | R6 batts to floor |
| Windows | Single glazed aluminium | Double glazed aluminium |
| Hot water | Solar hot water system - gas boosted | Heat pump hot water – off peak |
| Rooftop Solar PV and Battery | N/A | 7.4 kW Solar PV system and 13kW battery storage |
| Heating and cooling | Gas ducted heating, no cooling | 2.5 star rated, 3kW split system reverse cycle heating and cooling system and slow combustion wood stove |
| Lighting | Maximum 5 W/m2 | 1.1 W/m2; energy-efficient LED lighting |
Table 2: Comparing the energy-efficient design features of the Ecoliv Yea home to the baseline 6-star home.
Home design
Ecoliv’s home in Yea, Victoria, is nestled in a valley where the Yea and Goulburn rivers meet where the homeowners have created a haven from the hectic pace of day-to-day city life. Sited with stunning western views, the design settles into the contours of the land. The windows and expansive sliding doors are designed to provide abundant natural daylight and uninterrupted views.
The modular home is autonomous on the site, producing its own power with a PV solar array and battery storage, capturing rainwater, and treating and disposing of wastewater with an on-site gravity fed system, eliminating operating costs of the home and adding to the overall environmental sustainability. Constructed to adhere to a BAL 29 the exterior is robust yet reflective of its natural location with the addition of accent timber decking.
Ecoliv pride themselves on creating modular prefab homes that have a minimal impact on the earth.
"We build homes that are designed with passive solar principles to ensure that the homes are comfortable all year-round. We aim to achieve a 7-star minimum with each project. To do this we ensure that the glazing is orientated in the right direction, with shading and cross-flow ventilation as well to make the house comfortable for our clients.”
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Ideally a home would have its living rooms orientated to the north with appropriate shading to allow for good solar access, however this was a challenge with the Yea home as the sweeping views of the valley were located to the west. The owners wanted a home that captured a view in each room and while good solar passive design is key, it’s not the only design consideration for achieving a more energy efficient home.
Other key considerations featured in this home include:
- above standard insulation levels of at least R5.0 for ceilings and floors
- energy efficient glazing, lighting and appliance choices.
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This home has a high level of insulation in the walls, floors and ceiling which are standard inclusions in Ecoliv’s homes. Being a prefab home means relying on the use of timber frame construction rather than timber framing for walls and ceilings with a concrete floor slab. As such, the home doesn’t carry much thermal mass and requires good levels of insulation to achieve its 7-star rating.
Ecoliv selected R6 insulation to ceilings and floors with R2.7 insulation in the walls to ensure that the home maintains a comfortable temperature for its owners.
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The selection of energy-efficient appliances combined with solar PV and battery storage mean the owners of this home can expect an annual energy bill of only $297.
- Thanks to its efficient thermal envelope this home can be heated and cooled with a 2.5-star rated, 3kW split system reverse cycle heating and cooling system and slow combustion wood stove. Split system air conditioners are the most efficient way to heat and cool a home and when paired with a solar PV system have a lowest environmental impact.
- Each bedroom, the main living space and the alfresco area in this home is fitted with a ceiling fan. Ceiling fans help to reduce the need for additional cooling and heating and boost thermal comfort in the home. The inclusion of ceiling fans in this home boosts the NatHERS rating by 0.1 star.
- As part of their standard offering Ecoliv includes a Sanden heat pump hot water system, attached to an off peak tarrif, the time of day that the hot water heating is used with the solar PV system will mean that efficiencies can be found in the costs of running the hot water system.
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This home features double glazing throughout. The double glazing allows the homeowners to capture the western views without compromising on comfort and reducing their heating costs.
Picture windows in the primary bedroom capture the stunning view, Yea home (copyright Ecoliv). Home construction
Traditional site-built houses can have significant air leakage, causing uncomfortable drafts, cold spots, condensation and mould due to poor construction practices. By building their homes in factory-controlled conditions Ecoliv can ensure better quality construction processes.
Also during construction key aspects of the thermal envelope, such as insulation, can be subject to human error. For example, an electrical trade could come in to fix up some wiring and not return the insulation back to its exact spot, resulting in a gap. However, this is reduced within prefab construction due to the controlled environment of the factory and ability for better levels of supervision of the build resulting in a home that will be more comfortable for the owners.
In addition to these considerations, Ecoliv homes can offset any residual greenhouse gas emissions with an appropriately sized solar PV array. The Yea home boasts a 7.4kW solar PV system installed on the roof which aids to offset the home’s emissions and further reduces the home’s energy use. The 13kW battery storage allows for the home to store the energy it produces further contributing to its off-grid goals.
Kitchen and dining areas, Yea home (copyright Ecoliv). As-built verification
Sustainability Victoria engaged an independent as-built verification assessor to ensure that the homes were built to meet their intended energy efficiency targets. The verification check included a blower door test and a thermography test.
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The homes were blower-door tested to determine the air leakage rate. The home passed the blower door test with an air-permeability ranges from 3.3 to 4.8 m3/m2.hr, which is well below the requirements of the National Construction Code.
If the homes had an air-permeability below 3 m3/m2.hr , then mechanical heat recovery ventilation would have been recommended, to ensure adequate fresh air is available to occupants.
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This test uses a specialised camera that can ‘see’ heat transfer, 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 five per cent of insulation is missing. The Ecoliv homes all passed with only a 4.1 per cent deficit in ceiling insulation coverage in one of the homes and an impressive 0% deficit in all walls.
Summary
Prefab homes can achieve high levels of energy efficiency and sustainability, alongside appropriate passive solar orientation. They can be highly valuable for complex or remote sites where it's difficult to find appropriate trades, and for off-grid living. Additionally, Ecoliv demonstrates that prefab homes can be well-designed with thoughtful detail towards the sustainability of the materials and the health of the inhabitants.
More information
Book a display visit or call 1800 326 548.