Orientation and design are the keys to star rating success
A render of the front façade of the Ordinary Miracle range (copyright Positive Footprints). Orientation is an easy win and is important when designing a 7-star home with Sustainability Victoria’s 7 star Upgrade Analysis showing a difference of up to a 1.2 Star NatHERS rating. Homes that are designed with orientation of the living rooms to the north, with appropriately sized windows and shading will perform well all year round.
The NatHERS star rating of a home reflects how well it is designed for orientation and northern aspects. Homes that have good orientation are also cheaper to run with a reduced energy load for heating and cooling leading to annual energy savings for the homeowners.
Achieving 7 stars and beyond doesn’t have to be difficult and that is proven by this well-designed home by Positive Footprints.
Snapshot
Builder: Positive Footprints
Location: Balwyn North, VIC 3104
Design: Based on Ordinary Miracle, part of the Carbon Zero Series
Description: Single storey, 3 bedrooms, 2 bathrooms
Size: Total area 235.78m2
House: 167.59m2
Deck: 51.6m2
Carport: 17.03m2
NatHERS energy rating: 8.6 stars*
Whole-of-home: all electric appliances, Solar PV, battery storage
Other features:
3 phase power, EV ready, energy efficient lighting, 7,000Lt rainwater storage, low embodied carbon concrete, recycled bricks from previous home. carbon offset concrete and plasterboard, low VOC paints and glues, EO cabinetry and trims throughout.
Annual emissions: -13.03 tonnes of CO2-e
Annual energy cost: -$473/annum
*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 bill amounts were calculated for this 8.6 star home showing that it is reaching beyond net zero emissions and will actually save the homeowners -$473/year on their energy costs through their choice of energy efficient, electric appliances. Additionally, this house has a 13kW battery to store the extra energy as well as charge the owner’s electric vehicle.
Home design
There are some key design features that have provided this home with its high energy rating, including orientation, insulation, thermal mass, windows and shading. In combination, these qualities create a highly energy-efficient home which will maintain comfortable internal temperatures for its owners. Some of the key decisions involved in this home achieving its beyond 7-star NatHERS rating are outlined below:
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Increased insulation level in the design is an important and cost effective way to achieve a higher NatHERS rating, especially if changes to the home’s orientation are unable to produce the desired result. Enhanced insulation offers improvements to annual energy use, thermal comfort levels, and noise reduction.
Typical insulation upgrades to support a higher star rating include upgrading:
- ceiling insulation from R4.1 to R5.0 or R6.0 batts
- external wall insulation from R1.5/2.0 to R2.5/2.7 batts
- insulation in internal walls between wet and non-wet areas, between the ground and first floor (in second story dwellings) and between the home and the garage.
Good insulation installation requires that the batts are flush to the studs, leaving no gaps or cracks, with minimal compression, all junctions and lintels insulated with pipes and wires chased in.
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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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Materials with thermal mass absorb heat from the air in the room or from the sun shining on them. This heat is then released slowly into the room over several hours. To get the best out of high thermal mass materials they must be in contact with the internal air so that heat is free to flow into and out of them. Putting carpet or timber on a slab floor reduces this ability. Concrete slab floors are made of high thermal mass materials. Like internal brick walls they absorb heat from direct sunlight or inside air during the day and store it. To find out more about thermal mass see the Energy Smart Housing Manual (PDF, 7MB).
Using thermal mass in north-facing rooms should be a priority, particularly on those walls which receive direct winter sun because this is where the heat gains from the sun are highest in winter.
On this project, due to sloping ground, and a desire for single level accessibility, the builders started on the high side of the block with slab on ground but ended up with suspended concrete where the land fell away. The suspended slab sits on brick subfloor wall & piers, recycled from the previous home, above EcoPact Zero carbon offset concrete strip footing - lowering the embodied carbon.
For maximum effectiveness, thermal mass should be insulated from external air temperatures. The insulation should be located on the outer side of the thermal mass and allow the internal layer of thermal mass to come in to contact with the internal air. In this home, the vertical edge of the slab was covered with 30mm XPS Board insulation, which was neatly concealed under the battened off cladding. -
Windows are a key aspect of achieving a higher star rating as they are the main area of weakness in the thermal performance of a home. It is recommended that all windows are upgraded to double glazing from a comfort perspective and to reduce condensation on cold days. However, if that is cost-prohibitive not all windows need to be upgraded to achieve a 7-star rating. In some cases, this can be achieved with a mix of double and single glazing which helps to keep costs modest. It is recommended that the largest living zone windows are upgraded first. As they have the biggest impact on the star rating.
One possible way to achieve a better star rating without increasing costs to the client could be by reducing window size. This option should be weighed up against other considerations such as the buyer’s wishes, the architectural features of the home and the requirements of the National Construction Code for minimum natural light.
It is important to also consider shading, as the lack of adequate shading can lead to the home overheating in summer and therefore make it difficult to achieve a 7-star NatHERS rating. Shading is often provided through appropriately sized eaves, which cut out the harshest summer sun, but allow the sunlight to enter in winter when the sun is lower in the sky. For more information on passive solar design and appropriate shading design refer to the Energy Smart Housing Manual (PDF, 7MB).
The polished concrete floor in the north-facing living areas of the Positive Footprints home (copyright Positive Footprints). As-built verification
Sustainability Victoria engaged an independent as-built verification assessor to ensure that the home was built to meet the intended energy efficiency targets. The verification check included a blower door test and a thermography test.
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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 2.77 m3/m2.hr.
Homes with a low air leakage rate require an appropriate ventilation strategy, as described above, 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 passed with an impressive 0% deficit in all walls and floor demonstrating the quality of the insulation installation.
Summary
This home by Positive Footprints focuses on good orientation and smart design, which in combination with insulation and thermal mass of the property deliver a high star rating. High performing glazing with appropriate shading rounds out the design and ensures that the owners of this home will have a comfortable and well-performing home for many years to come.
More information
Check out Positive Footprint’s Carbon Zero Series which has clever design options to suit the full range of orientations.