NatHERS Star Rating

If you are planning to build a new building or undertake a major extension and alteration, then you will need to obtain an NatHERS star rating report for your building permit application. Nationwide House Energy Rating Scheme (NatHERS) assessment (NatHERS rating) is one of the avenues to satisfy the minimum energy rating requirements. Currently, 6 star energy rating is required for apartment units and 7 star energy rating is required for dwelling.

A dwelling in a green area having a 7 star NatHERS rating

Do I Need a NatHERS Star Rating?

What is 6 Star Rating?

House rating or NatHERS rating involves using a simple software to model a house in 2D. In these projects, we use insulation values close to the minimum requirements of the NCC. The software then calculates the necessary heating and cooling energy to maintain the occupants’ thermal comfort. The required thermal energy is then converted into a NatHERS star band, between 0 and 10 stars. Under NCC 2019, if your house achieves a 6 star energy rating or more, then you get an NatHERS Certificate. NatHERS star rating may also be used for ESD reports where council asks you to obtain house rating for BESS Best Practice assessment in Victoria. Also, for an alteration/addition to a building with an existing Star Rating, another assessment needs to be made. Details are explained here.

What Do the NatHERS Star Bands Mean?

The Housing Industry Association estimates that almost 71% of residential buildings use NatHERS star rating as a way to obtain energy rating report [reference]. Also, a higher NatHERS rating means that the house requires less artificial or active heating and cooling. In fact, the highest NatHERS rating could be obtained for a green 10 star rating.

What Building Classes Need NatHERS Rating?

A building that doesn’t require a building permit also doesn’t need to comply with energy efficiency requirements (i.e. doesn’t require a NatHERS rating or any other method of compliance). We undertake NatHERS star rating for developers seeking for a NatHERS Certificate. The following NCC building classes may need an energy rating report:

  • A 0 star house rating means the building fabric does nothing to maintain comfort levels inside the house.

  • A 5 star house rating is the thermal comfort level you feel in houses built between 2005 to 2011 in Victoria.

  • A 6 star energy rating is the minimum level of compliance as per National Construction Code 2019*.

  • A Green 10 star rating house is the highest NatHERS rating available.

  • Class 1a dwelling: detached house or one of a group of attached dwellings including row house, terrace house, townhouse or villa unit. 

  • Class 2 buildings: an apartment building (multi-residential) containing two or more sole occupancy units. In the case of a multi-residential, the whole building collectively (not each unit) must achieve a 6-star average (each being 5-star minimum) under NCC 2019.

  • Class 4 part of a building: a sole residential dwelling inside a non-residential building.

According to VBA, 6-star houses use 24% less thermal energy compared to 5-star houses..

NatHERS star rating doesn’t cover Class 1b buildings or Class 3 hotels, For more information on building classes, click here.

What do the energy rating stars represent?

The Housing Industry Association estimates that almost 71% of residential buildings use star rating as a way to demonstrate energy efficiency compliance [reference]. A higher star rating means that the house requires less artificial or active heating and cooling.

 

  • A 0-star house means the building fabric does nothing to maintain comfort levels inside the house

  • A 5-star house is the thermal comfort level you feel in houses built 2005 to 2011 in Victoria.

  • A 6-star house is the minimum level of compliance as per National Construction Code*.

  • A 10-star house is a 100% passive house with absolutely no artificial heating and cooling to keep the house temperature and humidity at comfort levels.

*According to VBA, 6-star houses are projected to use 24% less energy for heating & cooling compared to 5-star houses.

What building classes need an energy rating?

A building that doesn’t require a building permit also doesn’t need to comply with energy efficiency requirements (i.e. doesn’t require a star rating or any other method of energy compliance). NatHERS energy rating can be used for demonstrating energy compliance for all residential dwelling such as:

  • Class 1a dwelling: detached house or one of a group of attached dwellings including row house, terrace house, townhouse or villa unit. 

  • Class 2 buildings: an apartment building (multi-residential) containing two or more sole occupancy units. In the case of a multi-residential, the whole building collectively (not each unit) must achieve a 6-star average (each being 5-star minimum).

  • Class 4 part of a building: a sole residential dwelling inside a non-residential building.

Star rating scheme doesn’t cover Class 1b buildings, For more information on building classes, click here.

What Are PROS and CONS of NatHERS Star Rating?

PROS

NatHERS Star Rating method is cheaper to undertake, and perhaps more cost-effective for small and medium-sized houses with a low window ratio. Also, a 6 star energy rating is fast to assess and it costs less in terms of the assessor’s fee.

Dwellings with green roofs for NatHERS star rating

CONS

NatHERS star rating compares the annual heating and cooling energy demand to that of a standard 200m2 house. The complete range of stars from 0-10 is called NatHERS star bands. Depending on the conditioned area of the house, if the house is larger or smaller than 200m2, extra stars are removed or added to the house rating. For houses larger than 200m2, the floor area correction factor works as a penalty and it may increase construction costs. The figure below shows the major impact of area correction penalty on big houses.

Also, NatHERS star rating is a simple way of assessing a building load and doesn’t take into account the complexity of the heat transfer to/from the building. This sometimes leads to a high construction cost and especially the glazing. In these instances, we prefer Verification methods compared to obtaining a NatHERS Certificate.
We cannot use a NatHERS rating building model for any other purposes like CFD modelling or daylight modelling. The model can solely be used for the house rating.
A suspended home in woods

NatHERS Energy Rating Requirements in Victoria

Getting a 6 star energy rating in Victoria depends on your house design, obviously. The table on the right shows the minimum performance requirements in accordance with the NCC 2019 provisions. However, having these minimum thermal performance requirements will not grant you a 6 star energy rating in Victoria. To achieve a cost-effective NatHERS Certificate, your house design must be similar to a standard house design (in the eyes of the NCC) as much as possible. Consequently, some of the standard house design characteristics (as obtained from the NCC 2019) is described below.

Standard Home Design

1- Floor type: concrete slab on ground
2- Ceiling type: flat
3- Ceiling height: 2.4m
4- Pitched roof: not more than 23 degrees
5- Roof lights: no roof lights
6- Window area: not more than 10% of the floor area of the room served.
7- Wall type: no lightweight walls

The more different your home design is from the above, the less likely for it achieves a 6 star energy rating. Additionally, this means you will need to add more insulation to the roof, floor and walls or to install windows with lower U-value to obtain a6 star energy rating. Ultimately, some complex or luxurious designs may even fail to obtain a NatHERS star rating with a meaningful window U-value. In these situations, VURB is an alternative pathway that serves as a tool to maintain construction costs while preserving the energy efficiency of the house.

Climate zone67
Major cityMelbourneHobart
RoofR5.1
(solar absorptance >0.4)
R4.6
(solar absorptance <0.4)		R5.1
(solar absorptance >0.4)
R4.6
(solar absorptance <0.4)
Roof solar absorptanceSee aboveSee above
External wallsR2.8R2.8
Wall solar absorptanceNo requirementNo requirement
Glazing
U-value & SHGC		from ABCB Glazing Calculatorfrom ABCB Glazing Calculator
Roof lights
U-value		Depends on shaft index – U3.4 to U8.5Depends on shaft index – U3.4 to U8.5
Roof lights
SHGC		Depends on shaft index – 0.34 to 0.83Depends on shaft index – 0.34 to 0.83
External shadingNo limitNo limit
Concrete slab on ground
(no slab heating)		No requirementNo requirement
External floorR2.25R2.75

What are the Alternatives to the NatHERS Star Rating?

Considering the pros and Cons of the NatHERS rating, it is worthwhile to consider all other options available for a residential building energy compliance. These are:

energy compliance

Elemental Provisions or DtS (Deemed to Satisfy method)

This is a low cost and least time-consuming compliance method. The Deemed to Satisfy (DTS) report provides a list of minimum prescriptive insulation values and thermal performance requirements to meet the National Construction Code (NCC).

DTS compliance is fast (we can do it in a single day), low cost, and simple. The disadvantage is that the solutions based on DtS are limited and may not be suitable for your architectural design, also it could be expensive to construct.

This option is recommended for small and simple buildings with small glazing area and we always try it first. Note that this option is rigid and doesn’t allow a trade-off between different building fabric insulation or glazing.

6 star energy rating , House rating, 6 star energy rating requirements, nathers star rating, nathers rating, energy rating report , 6-star energy rating requirements victoria, 6 star energy rating house, green 10 star home, 6 star energy rating victoria , nathers star bands , nathers certificate, NatHERS 7 star rating house

Verification Using Reference Building (VURB)

This is the ultimate energy compliance avenue. It involves modelling your building and modelling a similar house based on minimum energy efficiency requirements (i.e. elemental provisions). Additionally, it eliminates all the cons of NatHERS energy rating and allows for more accurate thermal energy modelling of your house. The main advantage of this approach compared to the star rating approach is that this option may allow you to save more construction costs.

This option is highly recommended for high-end houses with large glazing area. Also, it allows for a trade-off between different building fabric insulation and glazing thermal performance to meet NCC Performance Requirements. This option proved to work even for the most costly-to-construct houses.

Elemental Provisions (Deemed to Satisfy method)

Verification Using a Reference Building (VURB)

This is a low-cost and least time-consuming method compared to NatHERS star rating. The Deemed to Satisfy (DTS) report provides a list of minimum prescriptive insulation values and windows thermal performance to meet the requirements of the NCC.

Also, DTS compliance is fast (we can do it in a single day), low cost, and simple. The disadvantage is that the solutions based on DtS are limited and may not be suitable for your architectural design, also it could be expensive to construct.

This option is recommended for small buildings with low glazing ratios. Also, this method doesn’t allow trade-off between insulation and glazing.

This is the ultimate energy compliance pathway. It involves modelling your building and also, modelling a similar house having the minimum energy efficiency requirements. Generally, It eliminates all the cons of NatHERS star rating method and allows for an accurate energy modelling of your house. The main advantage of this approach compared to the NatHERS rating approach is that this option allows you to save on construction costs.

This option is highly recommended for high-end houses with large glazing ratios. Additionally, it allows for a trade-off between different building fabric insulation and glazing thermal performance. The Verification method proves to work better for most houses compared to the house rating schemes.

What is NatHERS Certificate?

The Nationwide House Energy Rating Scheme (NatHERS) was first announced in 1993. NatHERS is a system that rates dwellings and apartment buildings based on their energy efficiency and thermal performance.

An accredited NatHERS assessor uses a NatHERS tool (e.g. First Rate 5) f0r a house rating assessment. Then, a the software generates a NatHERS star band. Consequently, by submitting the model, you can obtain a NatHERS Certificate for the house. This certificate shows that the house achieves a 6 star energy rating or 7 star energy rating (depending on the version of NCC). Additionally, NatHERS star rating is by far the most attractive pathway to obtain residential energy compliance

What are the Steps of NatHERS Rating?

Initial Data Collection

Building Modelling

Zoning & Assignment

Star Allocation & Report

Initial Data Collection

Your assessor will need a plan view, elevation views, section cuts, glazing schedule and building fabric materials to start the energy rating process.

Building Modelling

The assessor models the geometry of the building in two-dimensions and assigns each room as an individual zone.

Zoning & Assignment

The assessor then assigns Building fabric, glazing performance, internal gains, condition type and other internal conditions to the model.

Star Allocation & Report

After several iterations the assessor reaches compliance. Then, the assessor issues for a NatHERS Certificate and conducts an energy rating report.

Your assessor will need a plan view, elevation views, section cuts, glazing schedule and building fabric materials to start the energy rating process.

The assessor models the geometry of the building in two-dimensions and assigns each room as an individual zone.

The assessor then assigns Building fabric, glazing performance, internal gains, condition type and other internal conditions to the model.

After several iterations the assessor reaches compliance. Then, the assessor issues for a NatHERS Certificate and conducts an energy rating report.

How long does it take to finalize a NatHERS energy rating report?

For a medium-sized house (approximately 160m2), it will take us 2 to 3 days to finish the energy rating report. Also, the degree of complexity of the building’s geometry and its features is a determining factor in the final NatHERS star rating project deadlines.

How much does it cost to get a NatHERS energy report?

This depends on the size and complexity of the building. Multiple types of windows, multiple levels and adjacent shading elements, adds to the complexity of the work. Also, the same efforts goes to the 7 star energy rating houses.

Further information on
NatHERS Rating

If you have further questions about 6 star energy rating or 7 star energy rating, refer to the following links or contact us.

PDF – Victorian Building Authority 6 star fact sheet.
PDF – Victorian Building Authority Practice Note 55.

Our Past NatHERS Star Rating Projects

At Energy Compliance Consultants, we have broad experience in Residential – Mixed Use and commercial projects. Here are some of our NatHERS rating projects. Also, See our Projects webpage for more.

  • Our NatHERS Star Rating project at Gordon
    Gordon – NatHERS rating and Performance Solution (VURB)

  • Ashwood- NatHERS rating
  • Elevation view of our NatHERS star rating project at Wonga Park

    Park Orchards- NatHERS rating

See above that Gordon house has also required a VURB Performance Solution! Sometimes, some high-end houses with large glazing to floor ratios are very expensive to build using the NatHERS star rating. The Last resort in these cases will be Verification Using a Reference Building (VURB) under NCC.

Which factors would help to obtain a NatHERS Certificate?

When a house, as currently designed doesn’t meet the minimum 6 star energy rating (under NCC 2019), there are a few solutions to improve the energy efficiency rating.

National Construction Code recognizes 8 climate zones in Australia. These climate zones vary from hot humid climate (Zone 1) to Alpine areas cold climate (zone 8). Some of the following strategies apply to all climates and there are also some climate-specific strategies.

Each house might perform differently depending on its climate and micro-climate zone. Therefore, it is highly recommended to get your ESD Consultant involved from the early stages of design. Also, note that NatHERS star rating may not be the best pathway for your development to meet the minimum energy efficiency rating.

Common Strategies for all Climates

  • Insulate ceilings and walls.
  • Use appropriate shading for glazing.
  • Minimize west and east-facing glazing or use adjustable shading devices to adjust the level of heat gains from the sun.
  • Weather-seal all external windows and doors.
  • Use appropriate openings (windows and doors) for an effective natural ventilation and passive cooling.

There are unlimited climate and micro-climate strategies that require different energy measures. Knowing these are essential in obtaining a cost-effective NatHERS Certificate. Here, we classify them into two major strategies.

Strategies for heating dominant houses – Cold climates

Strategies for cooling dominant houses – Hot climate

House rating, green 10 star home, 6 star energy rating, nathers star rating, 6 star energy rating requirements, nathers rating, energy rating report, 6-star energy rating requirements victoria, 6 star energy rating victoria, nathers star bands, nathers certificate, 6 star energy rating house

Orientation

 

For heating dominant houses, choose a house orientation to take advantage of solar energy. This can inherently add 1 star to your building. To achieve a cost-effective NatHERS rating, the long face of the house should be aligned to the north as solar gain in winter can offset building’s demand for artificial heating.

For cooling dominant houses, choose a house orientation to restrict solar energy gain on east and west facades. This can inherently add 1 star to your building. To obtain a cost-effective house rating, the long face of the house should be aligned to the north and minimum wall-glazing areas must be aligned to the east or west.

6 star energy rating house, House rating, green 10 star home, 6 star energy rating, nathers star rating, 6 star energy rating requirements, nathers rating, energy rating report, 6-star energy rating requirements victoria, 6 star energy rating victoria, nathers star bands, nathers certificate Layout

 

For a heating dominant house, spaces used during the day should be arranged to benefit the most from daytime passive heating. It’s best to arrange daytime zones in a layout for them to have a large wall-glazing area facing north.

For a cooling dominant house, spaces used during the day should be arranged to have minimum wall-glazing to the east or west. Also, It’s best to arrange night time zones to face east/west and daytime zones to face north/south.

nathers certificate , 6 star energy rating house, House rating, green 10 star home, 6 star energy rating, nathers star rating, 6 star energy rating requirements, nathers rating, energy rating report, 6-star energy rating requirements victoria, 6 star energy rating victoria, nathers star bands
Thermal mass

 

For heating dominant houses, maximize thermal mass where solar heat can be absorbed on the north side of the house. Generally, there is not much benefit in adding thermal mass to areas with limited or no solar access.

For cooling dominant houses, minimize thermal mass where solar heat is intense (i.e. east/west facades). Generally, there is not much benefit in having construction materials with high thermal mass in hot climates.

nathers star bands , nathers certificate , 6 star energy rating house, House rating, green 10 star home, 6 star energy rating, nathers star rating, 6 star energy rating requirements, nathers rating, energy rating report, 6-star energy rating requirements victoria, 6 star energy rating victoria
Floor

 

For heating dominant houses, it’s best to have a concrete slab or a waffle pod slab. Stored heat inside the ground is beneficial to offset the heating demand in winter. Also, in the case of a suspended timber floor, it’s better to add thick insulation and make it enclosed.

For cooling dominant houses, there is not much of a difference between a concrete slab or a suspended timber floors. However, concrete slab on ground is better for passive cooling. In the case of a suspended timber floor, it’s better to add a thin layer of insulation and make the subfloor ventilated.

6 star energy rating victoria , nathers star bands , nathers certificate , 6 star energy rating house, House rating, green 10 star home, 6 star energy rating, nathers star rating, 6 star energy rating requirements, nathers rating, energy rating report, 6-star energy rating requirements victoria
Insulation

 

For heating dominant houses, increase insulation to more than the minimum requirements. Glazing is one of the biggest costs in energy efficiency rating projects. Generally, a moderate to high insulation levels helps reduce costs. Also, Reduce the insulation on the north-facing walls that have high thermal mass.

For cooling dominant houses, adding high insulation to the walls may fail the building to transfer its internally generated heat so It’s better to add moderate amount of insulation. Also, reflective insulation is one of the best ways of insulating roofs and walls facing east/west.

6-star energy rating requirements victoria, 6 star energy rating victoria , nathers star bands , nathers certificate , 6 star energy rating house, House rating, green 10 star home, 6 star energy rating, nathers star rating, 6 star energy rating requirements, nathers rating, energy rating report
Albedo

 

Maximize solar absorptance of external surfaces (e.g. roof and walls) in heating dominant houses. Also, it is best to increase the reflectivity of decks or other surroundings of the house. Generally, a metal roof with a solar absorptance value of more than 0.7 (e.g. Monument) is preferred to increase the solar heat gain and a cost-effective NatHERS star rating.

Minimize solar absorptance of external surfaces (e.g. roof and walls) in cooling dominant houses. Also, it is best to increase the solar absorptance of decks or other surroundings of the house. Generally, a metal roof with a solar absorptance value of less than 0.45 (e.g. Surfmist) is preferred for the purpose of solar heat restriction and to obtain a costly NatHERS rating.

energy rating report , 6-star energy rating requirements victoria, 6 star energy rating victoria , nathers star bands , nathers certificate , 6 star energy rating house, House rating, green 10 star home, 6 star energy rating, nathers star rating, 6 star energy rating requirements, nathers rating
Glazing

 

Try to offset heating demand by allowing more solar radiation into a heating dominant house. Glazing with higher values of solar heat gain coefficient (SHGC) assists the building in achieving a cost-effective 7 star energy rating. This is especially the case for north-facing windows. Also, it is always better to avoid or minimize shading to the north-facing windows.

Try to offset cooling demand by allowing less solar radiation into a cooling dominant house. This is especially the case for east-facing and west-facing windows. Also, apply shutter blinds or adjustable shading devices to these windows. Avoid skylights where possible or decrease its SHGC, try and use north-facing dormers instead (where possible). It’s better for the house rating that the skylights face southwards.

nathers rating, energy rating report , 6-star energy rating requirements victoria, 6 star energy rating victoria , nathers star bands , nathers certificate , 6 star energy rating house, House rating, green 10 star home, 6 star energy rating, nathers star rating, 6 star energy rating requirements
Shading

 

For heating dominant houses, minimize shading to the north-facing windows and walls. For a cost-effective NatHERS rating, it is wise to use adjustable shading instead of permanent shading to the east-facing or west-facing windows. Also, optimize shading height and projection these windows to minimize glare and maximize winter solar gains.

For cooling dominant houses, maximize shading on all east or west-facing windows. Generally, for a good house rating, it is better to use high shading with short projection to the north-facing windows and low shading with long projection to the east or west-facing windows. The external shading over the northern windows shall be optimized to restrict solar gains in summer and allow it in winter.

6 star energy rating requirements, nathers rating, energy rating report , 6-star energy rating requirements victoria, 6 star energy rating victoria , nathers star bands , nathers certificate , 6 star energy rating house, House rating, green 10 star home, 6 star energy rating, nathers star rating
Air movement

 

The building must be well-sealed to restrict infiltration in heating dominant house. Infiltration is one of the major causes of heat loss for buildings located in cold climates. Try to have enough ventilation openings (5-10% of habitable spaces floor area) that allow for a good air movement during summertime. 

For cooling dominant houses, allow enough ventilation openings for habitable rooms. This allows a cool breezeway to form between one window in a room to another window in another room. Introducing an effective natural ventilation is the best way of reducing artificial cooling energy demand and to get a cost-effective NatHERS Certificate.

TIPS for a 6 star rating and an optimized house thermal performance

When a house, as currently designed doesn’t meet the minimum 6 star rating or some thermal measures are too expensive to install/construct, there are quite a few solutions to improve the energy efficiency cost-effectively. 

National Construction Code (NCC) recognizes 8 climate zones in Australia. These climate zones vary from hot humid climate (Zone 1) to Alpine areas cold climate  (zone 8). Some of the following strategies apply to all climates and there are also some climate-specific strategies.

Each house might perform differently depending on its climate and micro-climate zone, neighbouring building and shading from adjacent objects. It is highly recommended to get your energy assessor involved from the early stages so that they can work with your architect to quantify the impact of different measures on the overall house heating and cooling performance.

Common strategies for all climates

  • Insulate ceilings and walls.
  • Use appropriate shading for glazing.
  • Minimize west and east-facing glazing or use adjustable shading devices to adjust the level of heat gains from the sun.
  • Weather seal all external windows and doors.
  • Use appropriate openings (windows and doors) for cross ventilation and passive cooling.

There are unlimited climate and micro-climate strategies that require different energy measures. Here, we classify it into two major strategies.

Strategies for heating dominant houses – Cold climates

Strategies for cooling dominant houses – Hot climate

Star rating

Orientation

 

For heating dominant houses, choose a house orientation to take advantage of solar energy. This can inherently add 1 star to your building. For heating dominant houses, the long face of the house should be aligned to the north as solar gain in winter can offset building’s demand for artificial heating.

For cooling dominant houses, choose a house orientation to restrict solar energy gain on east and west facades. This can inherently add 1 star to your building. For cooling dominant houses, the long face of the house should be aligned to the north and minimum wall-glazing areas must be aligned to the east or west.

star ratingLayout

 

For a heating dominant house, spaces used during the day should be arranged to benefit the most from daytime passive heating from the sun. It’s best to arrange daytime zones in a layout for them to have a large wall-glazing area facing north.

For a cooling dominant house, spaces used during the day should be arranged to have minimum wall-glazing to the east or west. Also, It’s best to arrange night time zones to face east/west and daytime zones to face north/south.

star rating
Thermal mass

 

For heating dominant houses, maximize thermal mass where solar heat can be absorbed on the north side of the house. There is not much benefit in adding thermal mass to areas with limited or no solar access.

For cooling dominant houses, minimize thermal mass where solar heat is intense (i.e. east/west facades). Generally, there is not much benefit in having construction materials with high thermal mass in hot climates.

star rating
Floor

 

For heating dominant houses, it’s best to have a concrete slab as a floor construction. Stored heat inside the ground is beneficial to offset heating demand in winter. In the case of a suspended timber floor, it’s better to add thick insulation.

For cooling dominant houses, It’s best to have a concrete slab as a floor construction. Summer heat gains, as well as internal heat gains, can be transferred to the cool slab below. In the case of a suspended timber floor, it’s better to add insulation (not so thick).

star rating
Insulation

 

For heating dominant houses, increase insulation values to more than minimum requirements. Glazing is one of the biggest costs in energy efficiency measure and moderate to high insulation levels helps to reduce costs. Add less insulation to the walls with high thermal masses facing north.

For cooling dominant houses, adding high insulation to the walls may fail the building to transfer its internally generated heat so It’s better to add moderate insulation. Reflective insulation is one of the best ways of insulating roofs and walls facing east/west.

star rating
Albedo

 

For heating dominant houses, maximize solar absorptance of external surfaces (e.g. roof and walls). Its also best to increase the reflectivity of decks or other surroundings of the house. Metal roofs with solar absorptance values of more than 0.7 (e.g. Monument) are preferred for the purpose of solar heat gain.

For cooling dominant houses, minimize solar absorptance of external surfaces (e.g. roof and walls). Its also best to increase the solar absorptance of decks or other surroundings of the house. Metal roofs with solar absorptance values of less than 0.45 (e.g. Surfmist) are preferred for the purpose of solar heat restriction.

star rating
Glazing

 

For heating dominant houses, try to offset heating demand by allowing more solar radiation to the house. Glazing with higher values of solar heat gain coefficient (SHGC) may assist the building in demonstrating compliance with the NCC. This is especially the case for north-facing windows. It’s always better to avoid or minimize shading to the north-facing windows.

For cooling dominant houses, try to offset cooling demand by allowing less solar radiation to the house, especially east-facing and west-facing windows. Apply shutter blinds or adjustable shading devices to these windows. Avoid skylights where possible or decrease its SHGC, try and use north-facing dormers instead (where possible). It’s better for the energy use that the skylights face south.

star rating
Shading

 

For heating dominant houses, minimize shading to the north-facing windows and walls. It’s wise to use adjustable shading instead of permanent shading to the east-facing or west-facing windows. Optimize shading height and projection to the east/west-facing windows to minimize glare and cooling demand and maximize winter solar gains.

For cooling dominant houses, maximize shading on all east or west-facing windows. It’s better to use high shading with short projection to the north-facing windows and low shading with long projection to the east/west-facing windows. Shading to the northern windows shall be optimized to restrict solar gains in summer and allow it in winter.

star rating
Air movement

 

For heating dominant houses, the building must be well-sealed, that’s because infiltration is one of the major causes of heat loss in cold climates. Try to have enough ventilation areas (5-10% of habitable spaces floor area) that allow for good air movement during summertime. 

For cooling dominant houses, allow enough ventilation openings to habitable rooms. This allows a breezeway to form between one window in a room to another window in another room. Introducing natural ventilation is an effective way of reducing artificial cooling energy demand.

Going Beyond NatHERS Energy Rating

If your target is beyond the minimum energy compliance requirements of NCC 2019, or, you want to build a house that requires heating and cooling energy demand, you can achieve higher stars in NatHERS star bands. Consequently, NCC 2022 requires all new dwellings to obtain a NatHERS Certificate with a 7 star energy rating.

We also offer a similar service under passive house modelling. With this service, we assist homeowners and architects to quantify the energy cost saving from different passive solutions.

Range of Window U-value and SHGC for NatHERS Rating

Windows have two thermal properties that are directly related to the energy efficiency of a building:
U-value and SHGC.
Window SHGC is its ability to transmit solar radiation (both visible and infrared) from its exterior to interior; whilst window U-value is its ability to transmit heat from its hot face to the cold face (i.e. thermal conduction).

According to the AGWA, a typical range of window U-values varies between 2.0-10.0 W/m2.K (from the most energy efficient to the least).
Generally, window U-values depend on the glass type, glass panes, frame material, vision area and use of thermal breaks. Here, we quantify the range of window U-values and SHGC for typical windows in the Australian market.

Daylight Autonomy
Daylight Autonomy

What is a typical range for a window U-value and SHGC?

Windows have two thermal properties that are directly related to the energy efficiency of a building:
U-value and SHGC.
Window SHGC is its ability to transmit solar radiation (both visible and infrared) from its exterior to the interior; whilst window U-value is its ability to transmit heat from its hot face to the cold face (i.e. thermal conduction). According to the AGWA, The range of window U-values varies between 2.0-10.0 W/m2.K (from the most energy efficient to the least energy-efficient / cheapest).
Window U-values depend on the glass type, glass panes, frame material, vision area, use of thermal break and many more factors. Here, we quantify the range of window U-values and SHGC for typical windows in the Australian market.

Window Energy Rating in Australia

Each manufacturer has to test and declare certain window U-values and SHGCs for their products. To test these claims and to rate each window by its actual thermal performance, Window Energy Rating Scheme (WERS) is developed and is accredited by the Australian Fenestration Rating Council (AFRC). Also, you can access different products with the window properties of your choice using the following links.

Commercial Windows
                           
Residential Windows

The following are examples of such typical U-values and SHGCs from FR5 software that we use for our NatHERS rating projects. Also, these thermal performance values could be assumed for an existing window in a good shape.

Window ratings in Australia

Each manufacturer has to test and declare certain window U-values and SHGCs for their products. To test these claims and to rate each window by its actual thermal performance, Window Energy Rating Scheme (WERS) is developed and is accredited by the Australian Fenestration Rating Council (AFRC). Depending on the state you’re in and the type of building development, you can access different products with the window properties of your choice.

Commercial windows by state
Residential windows by state

Following are examples of such typical U-values and SHGCs from FR5 software accredited by AFRC. This thermal performance values could also be assumed for an existing window in a good shape.

Windows have U-value and SHGC as thermal performance
Single pane
Double pane (air-filled)

Clear

Tinted

Clear – Clear

Tinted – Clear

Aluminium
frame

U-value: U6.7 SHGC: 0.57 – 0.70

U-value: U6.6 SHGC: 0.41 – 0.49

U-value: U4.8 SHGC: 0.51 – 0.59

U-value: U5.2 SHGC: 0.35 – 0.39

Composite
frame

U-value: U5.9 SHGC: 0.57 – 0.65

U-value: U6.2 SHGC: 0.41 – 0.45

U-value: U3.9 SHGC: 0.51 – 0.59

U-value: U3.9 SHGC: 0.32 – 0.37

Fiberglass
frame

U-value: U5.4 SHGC: 0.56 – 0.63

U-value: U5.4 SHGC: 0.41 – 0.49

U-value: U3.0 SHGC: 0.48 – 0.56

U-value: U2.9 SHGC: 0.33 – 0.42

uPVC
frame

U-value: U5.4 SHGC: 0.56 – 0.63

U-value: U5.4 SHGC: 0.41 – 0.49

U-value: U3.0 SHGC: 0.48 – 0.56

U-value: U2.9 SHGC: 0.33 – 0.42

Timber
frame

U-value: U5.4 SHGC: 0.56 – 0.63

U-value: U5.4 SHGC: 0.41 – 0.49

U-value: U3.0 SHGC: 0.48 – 0.56

U-value: U2.9 SHGC: 0.33 – 0.42

Solutions for Expensive Windows in NatHERS Rating Projects

Compulsory thermal performance requirements for window U-value and SHGC are detailed in the NCC Vol 2.0, Part 3.12.2 for residential dwellings. This means if you want to know the acceptable range of U-values for your building, you need to follow Deemed to Satisfy (DtS) provisions of the NCC. You can obtain the acceptable range of DtS U-values and SHGCs using the ABCB Glazing Calculator for residential dwellings. Also, using tools like FR5, you can obtain a set of acceptable windows that grant you 6 star energy rating (for NCC 2019) or 7 star energy rating (for NCC 2022). But what if you need to go beyond these rigid DtS provisions? In such cases, you need to undertake a Performance Solution instead of following NCC’s Performance Requirements. For instance, JV3 modelling is a well-known Performance Solution for commercial buildings and VURB modelling is a Performance Solution for residential dwellings.

FAQ

FAQ for NatHERS Rating

Approximately 71% of residential buildings use the NatHERS Star Rating Scheme as a way to demonstrate energy efficiency compliance with the National Construction Code. To obtain a building permit, one of the required documents is an energy report. There are several ways to obtain this:

Among them, the NatHERS Rating presents a scheme to rate residential buildings based on their energy demand for space heating and cooling.

All residential dwellings such as the following buildings can use NatHERS star rating for their energy reports:

  • Class 1a dwelling: detached house or one of a group of attached dwellings including townhouses.
  • Class 2 buildings: an apartment building (multi-residential) containing two or more sole occupancy units. In the case of a multi-residential, the whole building collectively must achieve a 6 star average.
  • Class 4 part of a building: a sole residential dwelling inside a commercial building.

NatHERS star rating scheme doesn’t cover Class 1b or Class 3 buildings.

NatHERS rating is an assessment method for small and medium-sized dwellings and apartments (Class 1a and Class 2 buildings). However, it is better to use the Verification Method for big houses with complex geometries. This is largely due to the fact that the NatHERS floor area correction factor for large houses works against your benefit. This may increase the building’s construction costs (for example: the requirement of expensive windows).

Other building types, like board houses (Class 1a), hotel rooms or dormitories (Class 3) cannot use the NatHERS star rating method.

Yes. In Victoria, the Victorian Building Authority (VBA) continuously publishes and maintains practice notes. This is to provide guidance on the energy efficiency requirements of the Building Act 1993, Building Regulations 2018, and the NCC. There are two practice notes that are directly related to residential buildings’ energy efficiency compliance:

  • New Residential Buildings: Practice Note EE-03 (link)
  • Alterations to Existing Class 1 Buildings: Practice Note EE-04 (link). This Practice Note provides guidance on the energy efficiency requirements via star rating for alterations to an existing Class 1 building project.

If you have further questions about 6 Star energy rating for energy compliance of your building, contact us.

With the old standard of NCC 2019, a 6 star energy rating dwelling passed the thermal performance requirements; however, the new standard of 2022, requires at least a 7 star energy rating.

Yes. NatHERS star rating can be used to rate dwellings and apartments. It is a key assessment tool for conducting ESD reports using BESS Best Practice in Victoria. For alteration/addition to a building with an existing star rating, other assessment needs to be made where details are explained here.

The main PROS of NatHERS star rating method of energy compliance are:

  • NatHERS rating is a low-cost assessment method for small and medium-sized houses.
  • This method takes between 1 or 2 days to complete for most residential buildings and it is 5 times faster than the detailed energy assessment method.
  • NatHERS star rating is issued as an official rating with a traceable QR code. You can download the certificate online anywhere, anytime. This can be used in marketing the house for future sale.

The CONS and limitations of the NatHERS star rating method are:

  • Houses larger than 200m2 get penalized by FACF (Floor Area Correction Factor).
  • NatHERS star rating compares the annual heating and cooling energy demand to that of a standard 200m2 house.
  • This method is a simple way of assessing a building’s demand and doesn’t take into account the complexity of the heat transfers to/from the building. This sometimes leads to a high construction cost, especially the glazing.
  • NatHERS model could not be used for any other purposes like CFD modelling or daylight modelling. The model can solely be used by the NatHERS tools.
  • This method does not consider the impact of many building elements like slab edge insulation, reflected solar radiation and long-wave radiation inside the building.

Some of the limitations of NatHERS Star Rating method involves:

  • Class 1b buildings cannot use the NatHERS rating.
  • NatHERS rating compares your building with a Benchmark, which is a typical building in a similar climate.
  • This method does not consider the complexity and special features of your building.
  • It compares the heating and cooling demand of your building to a Benchmark. By reducing cooling demand you do not have necessarily a buffer to increase your heating demand, say, by installing a lower-cost window.
  • The NatHERS rating approach does not consider the physics of heat transfer (e.g. thermal mass or ground-coupling).
  • Using this compliance pathway, you cannot assess the Impact of fixed shading on solar heat gain.
  • NatHERS method can not capture time-dependent features such as operable shading devices or stored heat in the ground.
  •  

There are two alternatives to NatHERS rating:

  • Elemental approach: This is recommended mostly for minor renovations, alteration projects and small buildings.
  • Performance Solution approach: This is recommended for complex houses with a high ratio of windows. Generally, we use this method to reduce construction costs (like window costs).

The following parameters affect the NatHERS rating:

  • Orientation
  • Zoning and Layout
  • Thermal mass
  • Floor construction
  • Insulation level
  • Glazing thermal performance
  • Shading
  • Albedo
  • Air movement

Please refer here to learn how these factors have an impact on the NatHERS star rating.

Zoning is essential in the use of passive cooling and heating. This allows us to obtain the maximum NatHERS star rating, even before applying any insulation. A good zoning or layout for energy efficiency generally is:

  • To have living areas in the north
  • Having bedrooms on the south or east side of the building.
  • To have unconditioned areas on the east or west side of the building

Also, a good layout requires closing off parts of the house that occupants do not use regularly. In colder locations, it may even be beneficial to align living areas around the east and western sides.

Infiltration is one of the major causes of heat loss in cold climates. Try to seal the openings and also, have enough ventilation areas (5-10% of habitable spaces floor area) that allow for good air movement during summertime. There are several other factors contributing to heat loss in cold climates, including low-performing windows or thermal bridging. By eliminating these factors, you can obtain a low-cost 6-star rated house.

The best energy rating is a 10-star energy rating. However, it is very expensive to achieve a 10-star rating. NCC 2019 requires a building to achieve at least a 6-star energy rating. Under NCC 2022 a 7-star energy rating is the minimum.

There is no such thing as a “good energy rating”. The higher the NatHERS energy rating, the more energy efficient your home is. Getting to a higher star rating is very expensive. NCC 2022 sets a minimum 7 star energy rating for a residential dwelling.

FAQ for NatHERS Certificate

To obtain a NatHERS Certificate, first, you need to assess the building. In most cases, this takes between one and two days. At Energy Compliance Consultants, we need another day for fine-tuning and visualization of added insulation locations in our energy report.

No! To get your building permit, you need to assure authorities that your building is energy efficient. If you are undertaking a residential development of:

  • Class 1a building (dwellings)
  • Class 2 building (apartments)
  • Class 4 building (a sole-occupancy unit within a commercial building)

Then, one of the common ways of energy efficiency compliance is to obtain a NatHERS Certificate. Depending on the state and year of applying, your house may need to have a 6 star energy rating or 7 star rating.

For some complex designs with high ceilings or glazed walls, the building may fail to get a NatHERS Certificate, or, the construction costs get too high to obtain that. In these cases, VURB is the compliance method that we recommend to reduce building construction costs while achieving energy compliance.

This depends on the size and complexity of the building. Multiple types of windows, number of floor levels and multiple adjacent shading elements on the building, add to the complexity of the project. Contact us, and one of our team members will usually respond in less than 1 hour or leave a quote for your 6 star rating project.

Under NCC 2019, for:

  • Residential dwellings: a 6 star energy rating.
  • For apartments, an average NatHERS energy rating of 6 stars; with no units achieving less than 5 stars.

Under NCC 2022, for:

  • Residential dwellings: a 7 star energy rating.
  • For apartments, an average NatHERS energy rating of 7 stars; with no units achieving less than 6 stars.

Click this link to see the NCC 2022 adoption dates under your state.

FAQ for Energy Rating Report

This is a low-cost and fast method for energy compliance, in comparison with the Performance Solution. The Deemed to Satisfy (DTS) report provides a list of minimum prescriptive insulation values. It also includes the minimum thermal performance requirements for the glazing.

DTS compliance is fast (we can do it in a single day), low cost, and simple. There are two Deemed to Satisfy methods to obtain compliance with the BCA energy efficiency requirements:

  • NatHERS Star Rating: This method uses a simple 2D model and rates the building energy requirements on the scale of 0-10 star bands.
  • Elemental Provisions: This method doesn’t consider the whole house design and the trade-off between wall/roof/floor and glazing, it can be very expensive to implement in some instances. Also, this is a very rigid method for energy compliance as its requirements are a must-do. We recommend this option for small and simple buildings with small glazing areas.

For a medium-sized house (approximately 160m2), it will take us 2 to 3 days to finish the NatHERS energy rating report. The degree of complexity of the building’s geometry and its features is a determining factor in the final star rating project deadlines.

  • Description of the site and building
  • Modelling parameters and assumptions
  • Location of the required insulation
  • Location of the windows having specific performance values
  • Assessor credentials and modelling software used
  • Possible amendments to the drawings
  • Supplied Drawings date and revision
  • NatHERS Certificate

FAQ for 6 Star Energy Rating

Under the Nationwide House Energy Rating Scheme (NatHERS), all new houses and major renovations can use the Star rating approach. NatHERS energy rating is a way to demonstrate compliance with the energy efficiency requirements of the NCC.

Under NCC 2019, a 6-star energy rating is a minimum to achieve compliance with the code.

From May 2023, a 7-Star rating will be the minimum requirement for dwellings in Victoria.

There are several ways to improve your NatHERS energy rating which are low-cost. To improve your NatHERS rating, for instance, to have a 6-star energy rating house, you need to:

  • Add enough insulation to ceilings, walls and floors
  • Mitigate thermal bridging using thermal breaks or air spaces
  • Use appropriate openings (windows and doors) for cross-ventilation and passive cooling
  • Weather-seal all external windows and doors
  • Have shading with high projection over west-facing windows
  • Install external adjustable shading devices over east and west-facing windows
  • Utilize thermal mass in the living areas to absorb heat from northern windows

A 6-star energy rating involves using a simple computer modelling tool such as FirstRate5. First, you need to model the geometry of a house in two dimensions (floor plan). Then, you need and apply insulation, glazing performance values, and shading from adjacent elements. After entering several other parameters, the software calculates the area-adjusted heating & cooling demand of a house/apartment. Finally, the software converts the annual energy demand into a NatHERS star band of between 0 and 10. Under NCC 2019, if your dwelling achieves a 6-star rating or more, then you could obtain a NatHERS Certificate.

No, but following the NCC Reference Building‘s list of design criteria is a shortcut to ensure a cost-effective 6-star rating.

  • The following measures help you get a 6 star energy rating in Tasmania:

    • Double-glazed clear windows.
    • Optimum shading over north.
    • Orient living areas towards the north and bedrooms towards the south.
    • Have clerestory windows facing living areas.
    • Insulate concrete slab and slab edges or use waffle pod slabs.
    • Have a dark-coloured roof instead of light-coloured.
    • Have high thermal mass walls like double brick or thick concrete walls facing north.

    Note that Tasmania have not adopted NCC 2022 and therefore, 6 star energy rating is the minimum requirement for dwellings.

FAQ for 7 Star Energy Rating

NCC 2022 requires all new dwellings to satisfy a minimum 7-star energy rating. This applies to:

  • Houses – Class 1a,
  • Apartments- Class 2 and,
  • The residential part of commercial buildings, Class 4 buildings.

6-star energy rating was in effect since 2010 for almost 12 years.

A 7-star house has less artificial heating and cooling requirements and hence, emits less greenhouse gas emissions. Also, homeowners of a 7-star house pay less energy bills compared to a 6-star house. As a rule of thumb, a 7-star house requires 19% less heating and cooling compared to a 6-star house.

NCC 2022 requires all new dwellings to achieve a 7-star energy rating, succeeding the older version, which requires a 6-star energy rating.

NCC 2022 now requires a NatHERS 7 Star rating to satisfy thermal energy efficiency requirements. This used to be the NatHERS 6 Star energy rating under the previous version of NCC. There are still some allowances for outdoor living areas and ceiling fans to reduce NatHERS rating requirements in tropical climates (climate zones 1 and 2).

Under NCC 2022, we use the NatHERS star rating to meet the thermal performance requirements. These requirements are detailed in Specification 42 (S42C2) of NCC Volume Two (for Class 1 buildings) and clause J3D3 of NCC Volume One (for Class 2 buildings). The following are the new requirements and features that did not exist under the older version:

Updated Climate Files and Energy Star Bands

With the new NatHERS 7-star rating, NatHERS also updated the climate and weather files from its 2005 version. Along with updating the climate files, NatHERS has also updated the NatHERS star bands. Changes in the NatHERS Star bands are negligible. NatHERS has slightly reduced the new star bands to balance the effect of updated climate files.

Thermal Bridging

The New NatHERS 7-star energy rating requirements include the impact of thermal bridging. Thermal bridging is a major source of heat loss/gain that NCC 2019 didn’t consider a requirement for residential buildings. The impact of thermal bridging is major and is capable of dropping 0.5 stars. For instance, consider a typical 4 bedroom single storey house with metal-framed floors, walls and ceilings. If thermal bridging is properly mitigated in NatHERS modelling, it can improve NatHERS Rating by 0.4 stars in Melbourne or Hobart and by 0.5 Stars in Sydney or Adelaide [CSIRO].

The whole of Home Rating

This new feature is a new requirement under NCC 2022 to push the housing industry towards the use of high-efficiency services. In addition to assessing the building envelope, the new NCC requires a Whole of Home rating to assess building services. This includes lighting, Cooking and plug-in appliances, air conditioning, heat pumps, domestic hot water, pool and spa pumps, and onsite solar electricity and hot water generation and storage/battery. This will push future home builders to use more efficient appliances to achieve NCC compliance. This will also close a loophole in NCC 2019 where some assessors were using onsite solar PV to offset high heating and cooling energy demand due to a low-performing building fabric.

The Whole of Home rating is different from the 7-star energy rating for the building envelope. The whole of Home rating ranges from 1 (poor) to 100 (net zero). NCC 2022 requires a 50 Whole of Home rating for apartments and 60 for houses as a minimum to achieve compliance.

The following summarizes the key energy efficiency comparisons between a 7-star rating and a 6-star rating.

  • Demands 8-20% less energy for combined heating and cooling

For instance, in Melbourne, the maximum combined energy requirement under 6 stars was 120 MJ/m2 which has now dropped to 110 MJ/m2 under 7 stars. The same limits for Brisbane under 6 stars and 7 stars are 120 MJ/m2 and 105 MJ/m2.

  • Generates 25% less greenhouse gas emissions

The Climate Council’s report associates an extra added star with a 25% cut in greenhouse gas emissions.

  • Cuts annual energy bills by an average of $500 and provides better thermal comfort for occupants.

Annually, a 7-star house would save households between $119 to $945 on heating and cooling electricity demands (reference).

  • Imposes less peak load strain on the electricity network.

If the houses are built to decrease peak demand, especially on cooling energy, the network adapts better to future increases in electricity consumption and blackouts would occur less often.

To get a cost-efficient 7-star energy rating, you need to build your house in accordance with the NCC Reference Building as much as possible.

Note that the following design criteria are not requirements for the NatHERS 7-star energy rating compliance. The closer your building design is to the following, the easier to get the required rating.

The characteristics of the NCC Reference building are:

  • Floor type: Concrete slab on ground
  • Ceiling type: Flat
  • Ceiling height: 2.4m
  • Roof: Pitched roof with not more than 23 degrees
  • Roof colour: Solar absorptance of no more than 0.6
  • Roof lights: No roof lights
  • Window type: Double-glazed windows
  • Window area: Not more than 10% of the floor area of the room served.
  • Window orientation: Increase north-facing windows, avoid east and west-facing windows
  • Shading: Large projection for east and west-facing windows
  • Wall type: Brick veneer
  • Wall colour: Solar absorptance of no more than 0.6
  • Internal walls: Insulate walls adjacent to unconditioned spaces
  • Ceiling penetration: Avoid large penetration areas to the ceiling insulation

Air movement: Have cross-ventilation openings and ceiling fans.

The insulation requirements vary between different building sizes and locations. However, the following are the proven ways of insulating to have a 7-star rating house:

  • Install a low-cost 60mm roof blanket (R1.3), which sits in between 20mm timber battens. This gives you a 0.2-0.5 NatHERS star rating.
  • Insulate the studs to the fullest, which is to use a 32 kg/m3 insulation with an R-value of R2.7.
  • If you are using metal studs or purlins, use thermal breaks to reduce thermal bridging.
  • Use reflective foil-faced insulations where there is an air space available above or near the installed insulation.
  • Insulate concrete slabs using EPS or XPS boards, especially in colder locations.

To have a NatHERS 7-star rating house, it’s best to have a concrete slab on ground as a floor construction. Not only does it reduce the need for active cooling, but also it is feasible in keeping the heat below the ground for cold seasons. If you are installing a suspended floor, avoid using metal joists as much as possible.

From May 2024, Victorian Councils require a 7-star rating house for a NatHERS Certificate. Needless to say, many architects and builders have concerns about the additional NatHERS star rating requirement. They know already how hard it is to build a luxury house with high-raked ceilings and glazing and to obtain a 6-star rating for it. So what is the solution here? Are we still able to build a house with a reasonable cost associated with this additional star? Here, we propose solutions to how you can adapt to these changes cost-effectively.

Orient yourself!

Orientation is a major part of this adaptation. You need to design your house in a way to reduce both heating and cooling demand consequently. Therefore, you need to design in a way that the zones with daytime activities face toward the north for better utilization of natural irradiation by the sun. The East and west façades need to be small in comparison to the north façade. The introduction of light through east and west façades is always bad news in summer and also not very helpful in winter.

Adapt at the beginning!

Building layout design is a critical stage and taking steps on the way to a more passive house, is essential at the initial design stage. A smart architect arranges the rooms in a way that more daylight is available in the daytime for living areas, avoiding them being adjacent to unconditioned rooms. As bedrooms contribute more to heating demands in winter and at night, it is wise to shrink their external walls and exposed fabrics as much as possible. Also, a high-raked ceiling is not a good idea for a night-time conditioned zone. The heating of such high-volume zones is very demanding mainly due to an elevated infiltration.

More mass towards the sun?

Depends on the climate you are in; high thermal mass walls may help. In cold climates, you need to face a wall with a high thermal mass (e.g. concrete wall, brick cavity walls or earth walls) towards the north and face the sun. Storage of heat in the daytime would be beneficiary at night-time when the ambient is colder. However, it is reasonable to avoid this to a certain degree in hot climates. Thermal inertia (a fancy word for a delay in cooling demand occurrence!) is tightly associated with thermal mass in hot climates which will lengthen the period for artificial cooling even hours after the sun is set.

Let it sit on the ground!

Based on our experience, a suspended floor is an awful choice if you are seeking higher star ratings. In a hot climate, a suspended floor deprives you of 0.5 to 1 star compared with the concrete slab on ground. Floor construction does not affect heating demand since you can insulate suspended floors enough to mitigate the difference; however, cooling demand is going to be an issue here. Note that the earth is cooler than the ambient air by a few degrees, additionally, building energy is transferred to the ground and hence, the ground temperature below the house is very moderate and near the comfort temperature. This facilitates decreasing the cooling demand in the hot season and beneficiary the overall energy saving of the house services.

Block the flow of heat at all costs!

A high degree of insulation is worth its cost. More insulation means more buffer to have cheaper windows with a low thermal performance. Try and diversify your choice of insulation. Reflective insulation works best in summertime and hot climates. The use of a roof blankets the flow of heat further in cold climates. Also, slab edge insulation and underslab insulation work very well in reducing heating demand in those climates. Remember, Adding R6.0 insulation to the ceiling is not the same as adding an R1.5 blanket to the roof and R3.5 to the ceiling; the latter is more effective (the lesser the cold faces the better and also less thermal bridging). Also adding a moderate amount of insulation to the internal walls adjacent to the unconditioned areas goes a long way in terms of heat transfer and acoustics.

Go a little bit easy on aesthetics!

The colour of external building elements matters, perhaps the most in extremely hot or cold climates. You need to maximize the solar absorptance (solar heat gain) of building elements in cold climates. Therefore, the use of dark-coloured external roof or wall claddings (similar to Monument or Basalt) is useful. On the other hand, for hot climates, you need to use light-coloured external elements (similar to Surfmist or Shale grey). Understandably, these choices may conflict with the aesthetics of the building and the choice of material. You need to assess the effect and see if it is worth your while.

Let there be more daylight!

The cost of a project mainly depends on the overall U-value of its windows. Windows play a major role in one’s sense of belonging and attachment to the environment as well as well-being. But it’s reasonable to ask to what degree? For example, the BCA requirement for natural light is that the light transmitting area of a window (i.e. glazing) be at least 10% of the floor area served. Also, an opening area of 5-10% to the floor area served is certainly ok for Climate zones 6-8 and probably sufficient for other climate zones as well. Going beyond the above thresholds comes with a price as you will need to decrease the overall U-value of windows.

As for window SHGC (Solar Heat Gain Coefficient), you generally need to maximise it on north-facing windows (i.e. clear windows). Also, try to minimise it on the east or west-facing windows (i.e. tinted windows). Note that south-facing windows do not matter much in terms of solar gain.

Optimize shadings

Perhaps, the best option here to obtain an additional star is to optimize your shadings and eaves. Here’s how it goes:

  • North-facing windows do not like shadings with long projections. In the summertime, the sun is directly above the house and therefore short shading projection is enough to block the unnecessary irradiation. As a rule of thumb, do not allow the shading projection (P) to be more than 50% of the window height (h) plus the distance from the top sill to the edge of the shading (G).
  • East and west windows do not help you in winter, however, they increase the cooling demand significantly in summer. Therefore, you need longer shading projections on them. The choice of retractable shading devices instead of fixed shadings is very helpful. Generally, this solution pays back and makes it easy to go beyond a NathERS 6-star rating.
Get a professional

We recommend involving an ESD consultant in the early stages. What you need is a trusted company with specialists in Energy systems and ESD consulting. This gives you the ultimate insight as to what necessary and cost-effective solutions are to achieve a 7-star rating. It is wise to ask for a sample energy report and see how they are handling a project. Also, you need to know how feasible are their propositions and how inclusive is their energy report.

FAQ for NatHERS Star Bands

NatHERS star bands show the heating and cooling energy demand per unit area of a house. For instance, a 6-star house in Melbourne has a maximum of 32 kWh per m2 of indoor areas.

  • A 0-star house means the building fabric does nothing to maintain comfort levels inside the house
  • A 5-star house is the comfort level you feel in a typical house in Victoria in the 2000s.
  • A 6-star house is the minimum requirement for houses before October 2023 in Victoria (subject to NCC 2019 requirements).
  • A 7-star house is the minimum requirement for houses after October 2023 in Victoria (subject to NCC 2022 requirements).
  • A green 10-star house essentially requires no artificial heating or cooling energy

Note that NatHERS star bands or values differ with the location to account for local climate variations.

The NatHERS star bands are categorized from 0 stars to 10 stars. These bands represent the maximum allowed annual heating and cooling demand of your building. This energy demand is shown on the NatHERS Certificate in terms of Megajoules per square foot area of habitable rooms.

The maximum star rating is 10-star energy rating. This equates to a Zero Energy Building (ZEB) that requires essentially no artificial heating and cooling.

According to NCC 2019, for Class 1 and Class 4 buildings, a 6-star energy rating is the minimum requirement. Also, for Class 2 multi-unit developments, an average of 6-star energy rating is required and all units must meet the minimum rating of 5-star.

Under NCC 2022, for a Class 1 or a Class 4 building, a 7-star energy rating is the minimum requirement. Consequently, for Class 2 multi-unit developments, an average of 7-star energy rating is required and all units must meet the minimum rating of 6-star.

Range of U-values

Energy compliance measures for windows

Compulsory thermal performance requirements for window U-value and SHGC are detailed in the NCC Vol 1.0, Section J1.5 for commercial buildings, and in NCC Vol 2.0, Part 3.12.2 for residential dwellings. This means if you want to know the acceptable range of U-values for your building, you need to follow Deemed to Satisfy (DtS) provisions in those volumes. For the years 2019-2022, the acceptable range of DtS U-values and SHGCs can be obtained from ABCB Facade Calculator for commercial buildings and ABCB Glazing Calculator for residential dwellings. But what if you need to go beyond rigid DtS provisions? In such cases, you need to undertake a Performance Solution instead of following NCC’s Performance Requirements. For instance, JV3 modelling is a well-known Performance Solution for commercial buildings and VURB modelling is a Performance Solution for residential dwellings

6 star energy rating , House rating, 6 star energy rating requirements, nathers star rating, nathers rating, energy rating report , 6-star energy rating requirements victoria, 6 star energy rating house, green 10 star home, 6 star energy rating victoria , nathers star bands , nathers certificate, layout for energy