Amira 25 by Metricon Homes
Amira 25 with Summit façade. Metricon’s Amira 25 display boasts a 7.1-star NatHERS rating, efficient all-electric appliances, and solar PV. Occupants of this home will benefit from increased comfort, improved health, and impressive savings on their energy bills. This home can be built on any block and comply with the 7-star minimum provided the floorplan is oriented to achieve higher performance outcomes.
Feature home snapshot
Builder: Metricon Homes
Location: 8 President Road Sunbury – Villawood Redstone Estate – NatHERS Climate Zone 60
Design: Amira 25 with Summit Façade
Description: Single storey, 4 bedrooms 2 bathrooms 2 living areas
Size: Total area: 235.46m²
House area: 182.08m²
Garage: 36.14m²
Outdoor room: 12.25m²
Portico: 4.99m²
NatHERS energy rating: 7.1 stars*
Whole-of-home assessment: All electric with solar PV
*This home has been rated using FirstRate5 5.3.2b under NCC 2019.
Energy and cost savings
Using Sustainability Victoria’s Whole of Home Pilot Tool, the estimated annual energy use, emissions and energy bills were calculated for this home and compared to the same home in a business-as-usual scenario under NCC2019, 6-stars with a typical mixed fuel appliance selection and no solar. Thanks to the 7.1-star NatHERS rating, the selection of all-electric appliances and Solar PV the new owners of this home are expected to save $1,645 annually on their utility bills.
| 8 President Road, if it were a mixed fuel 6-star home without solar | 8 President Road (actual – 7.1-star all-electric home with solar) | Savings [%] | |
|---|---|---|---|
| Annual energy use | 51,533 MJ | -9,723 MJ | 119% |
| tCO2-e emitted p.a. | 5.28 | -2.71 | 151% |
| Annual energy bill | $2,327 | $682 | 71% |
Table 1: Predicted annual energy use, emissions, and costs, including supply charge for the Amira 25 under a business as usual and as built scenario.
Amira 25 7-star upgrade and appliance details
| Feature | Amira 25 6-star | Amira 25 7.1-star (as built) |
|---|---|---|
| NatHERS rating | 6 stars | 7.1 stars |
| Design orientation | North-east to the street | North-facing |
| Insulation - ceiling | R3 batts to ceiling | R5 batts to ceiling |
| Insulation - external walls | R2.0 to external walls | R2.5 to external walls |
| Insulation - internal walls | No insulation for internal walls | R2 to all internal wet area walls |
| Glazing | Single glazed aluminium | Single glazed aluminium to sliding door in family, front door, and laundry |
| Hot water | Solar hot water system - gas boosted | Heat pump hot water |
| Rooftop Solar PV | Not required | 6 kW Solar PV system |
| Heating and cooling | Gas ducted heating, no cooling | Ducted reverse-cycle |
| Lighting | Maximum 5 W/m2 | 2 W/m2; energy-efficient LED lighting |
Home design
To elevate the energy rating of the Amira 25 from 6 to 7 stars, a number of small specification upgrades are required. The scope of the upgrades depends on orientation, as this home has been designed with an optimal orientation in mind. Some of the key decisions to ensure the Amira 25 achieves a 7-star NatHERS rating are outlined below:
-
This home does not have an ideal orientation, with the street frontage on the north-east side of the block. While it is easier to implement good passive solar design principles if the home is oriented along compass lines, The Amira 25 can achieve 7 stars across all orientations with minor adjustments.
To highlight the impact of orientation on NatHERS ratings, an orientation analysis has been conducted using FirstRate5. Rotating the floorplan with as-built specifications returns a range of possible ratings between 6.8 stars in its worst and 7.5 stars in its best orientation:
- The best orientation for this design is for the main living areas to be facing directly north.
- If north is towards the garage and bedroom side of the home the best solution is to flip the design along its street frontage. By flipping the design, NatHERS ratings in increase from 6.8 to between 7.1 and 7.5 stars. Flipping the design enables compliance without the need for expensive specification upgrades. The placement of the driveway and services on a block often prevents this flip from occurring. Relocating the driveway to enable a full flip of the design will be cheaper and result in improved thermal comfort outcomes compared to upgrading specifications to achieve 7 stars for this design in its worst orientation.
- To achieve 7 stars with north to the street frontage, the single glazed sliding doors between the family and outdoor rooms require an upgrade to a double-glazed alternative.
The reason this home has a significant difference between its best and worst orientations is due to good solar passive design. This floor plan has been designed with orientation in mind.
-
To achieve 6 stars, this home only requires single glazing (U = 6.23, SHGC = 0.66). To achieve its 7.1-star rating a combination of single- and double-glazed units has been used:
- The front entry, laundry, and sliding door between the family and outdoor living space remain unchanged from the 6-star design.
- All other windows were upgraded to argon filled double glazed aluminum units (U = 3.79, SHGC = 0.6) If north is to the street, additional double glazing is required to the sliding door in the family room, increasing the rating in this orientation from 6.9 to 7.1 stars.
- By double glazing the sliding door, the design rating for the Amira 25 display in Sunbury would increase from 7.1 to 7.3 stars. The total achievable NatHERS rating in the homes best orientation would be 7.7 stars.
-
To achieve a 6-star NatHERS rating the Amira 25 would only require R2 insulation in external walls and R3 insulation in the ceiling.
To achieve its 7.1-star rating:
- wall insulation has been upgraded to R2.5
- ceiling insulation has been upgraded to R5.0
- internal walls around wet areas have been insulated with R2.0 batts.
Extra care has been taken to ensure continuous coverage, with insulation installed in all external corners and junctions, around lintels, and inside bulkheads.
-
Upgrading from 6 to 7 stars and including all-electric appliances with solar PV means the residents of this family home will be saving 71% or approximately $1645 annually on their energy bills. Appliances upgraded in this home include ducted reverse-cycle heating and cooling, heat pump hot water and induction cooking. Additionally, a 6kW solar PV system ensures the owners get a net zero outcome and the maximum benefit of an all-electric home. The combination of efficient all-electric appliances and solar PV ensure this home is net zero for operational emissions and will achieve compliance with the NCC2022 Whole-of-Home energy requirements.
Amira 25 undergoing blower door testing as part of the 7 Star Homes Program. Home construction
Through their collaboration with SV, Metricon homes have developed strategies to ensure consistent installation of insulation and better air tightness outcomes. In order to achieve its designed 7.1-star rating, it is crucial the builder takes care to ensure the home performs as intended. Standard Australian construction practices often result in draughty and poorly insulated homes. The construction process for this home involved some additional steps ensuring quality built outcomes.
- Additional care has been taken when installing insulation, ensuring coverage is continuous and free from gaps. This includes around windows and at external corners and wall junctions which are commonly missed.
- A plaster airtightness strategy has been employed, this includes caulking of plaster to the concrete slab, caulking service penetrations and caulking and sealing around cavity slider doors.
- The ducted heating return air plenum has been sealed internally – this is not commonly done. Proper installation of ducted return air plenums significantly reduces air leakage and draughts in the home and increases the efficiency of ducted heating and cooling systems.
- 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. Quality exhaust fans ensure a healthy indoor environment.
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.
-
The home was blower-door tested to determine the air leakage rate. The home passed the blower door test with an air-permeability of 4.89 m3/h/m2 @ 50Pa, which is good result and well below the 7 Star Homes program requirement of 10 m3/h/m2 @ 50Pa.
-
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 0.72% deficit in ceiling insulation coverage and a 2.8% deficit in the walls.
Summary
Metricon’s displays in the Villawood Redstone Estate in Sunbury demonstrate how 7-star homes are light, bright and comfortable. The Amira 25 display is rated at 7.1 but can achieve up to 7.5 stars without upgrading specifications in its optimal orientation. The uplift from 6 stars has been achieved by upgrading select windows from single to double glazed units along with insulation upgrades.
Due to taking a solar passive approach, the Amira 25 required lower levels of insulation, leaving scope for additional upgrades as required based on climate zone or site constraints. Significant thermal performance improvements are gained by upgrading the large expanses of sliding doors to a double-glazed alternative. This upgrade results in the Amira 25 achieving between 7.1 and 7.7 in more optimal orientations. The choice to build all-electric with solar will save the occupants of this home 73% on their annual energy bills.