FAQ

6 STAR ENERGY RATING

6 Star energy rating is used by 71% of residential buildings as a way to demonstrate energy efficiency compliance with National Construction Code (NCC) 2019. 6 Star energy report is one of the necessary documents to apply for building permit. 6 Star energy rating is a simplified computer modelling approach which is fast and low cost to obtain. Alternatives to 6 Star rating are DtS approach which is recommended mostly for minor renovations and VURB which is recommended for complex houses with high number of windows to save in energy construction costs.

From October 2023, NCC 2022 will come into effect and all new houses and major renovations must comply with 7 Star energy rating. Star rating bands (Figure below) refer to maximum annual heating and cooling demand your building is allowed to use in terms of kWh per m2 of internal areas.

For instance, a 6 Star, 200m2 house in Melbourne, is allowed to have annual heating and cooling demand less than 31.7 kWh/m2 x 200m2 = 6300kWh for all its internal Class 1 areas.

At Energy Compliance Consultants, we provide 6 Star NatHERS energy rating Australia wide:

What are the PROS and CONS of Star Rating approach?

6 Star Rating PROS

6 Star rating is a low cost assessment method for small and medium-sized houses.

6 Star rating takes almost 1 day to complete for most residential buildings and it is 5 times faster than the detailed energy assessment method, VURB (Verification Using Reference Building).

6 Star rating is issed as an official rating with a traceable QR code to download certificate online. This can be used in marketing the house for future sale.

6 Star Rating CONS

Houses larger that 200m2 loose stars get penalized by FACF (Floor Area Correction Factor)

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 star bands. Star bands are based on thermal heating and cooling energy demand for houses in different locations. Depending on the total internal area of the house that is conditioned, if the house is smaller 200m², extra stars are reduced or added. 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, Star rating is a simple way of assessing a building demands 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, Verification methods are preferred and are proven to work very well if done by professionals.Star rating 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.

Slab edge insulation cannot be modelled in

Tips to achieve a cost-efficient 6 Star energy rating

You can always achieve energy compliance any house design. However, the target here is to achieve it cost efficiently without blowing the construction project budget. In following we discuss tips that assist improving house energy rating and at the same time assist with reducing energy construction costs.

Follow NCC Reference Building design criteria:

Following the NCC “Reference Building” list of design criteria is a shortcut to assure a cost effective energy compliance. NCC “Reference Building” is used to derive energy star bands that 71% of all house designs in Australia are compared to.

Note that the following design criteria are not a requirements for star rating compliance. The closer your building design is to the following, the easier 6 star compliance will be and it will cost you less in construction stage.

1- Floor type: concrete slab on ground (NCC V2.6.2.2)
2- Ceiling type: flat
3- Ceiling height: 2.4m
4- Roof: Pitched roof with not more than 23 degrees, solar absorptance = 0.6
5- Roof lights: no roof lights
6- Window area: not more than 10% of the floor area of the room served. North facing windows can be increased in cold climates to maximize passive heating of the house.
7- Wall type: 110mm Brick veneer, solar absorptance = 0.6

8- Internal walls: no major effect on performance

9- Artificial lighting: no major effect on performance

When we are having challenges in compliance or when the cost of glazing becomes excessive, we first investigate if the client is open to adopt any of the above design criteria to assist with achieving star rating. Even if a client doesn’t incorporate any of the above in the design, we can still achieve 6 star rating by adjusting insulation values, glazing parameters, permanent shades, … to achieve the 6 Star.

Finally, for some complex designs with high ceilings, glazed walls, light weight walls, the building may fail to get a 6 star rating with a meaningful window U-values and may need thermally broken windows or triple gazing. In these instances, VURB is the compliance method that we recommend to reduce building energy construction costs.

Add enough insulation to ceilings, walls and floors.

• 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

Orientation

All major cities in Australia marked in gray in figure below including are located below the tropic of Capricorn. For this area that covers Sydney, Melbourne, Adelaide and Perth, it is preferred to orient the house so that the long face of the house is aligned to the north. This allows maximizing passive heating and with the use of shades the cooling demand can be managed. Orienting a house to true north can easily add 1 star to your building.

For Darwin, Cairns and Townsville, the building will receive sunshine from all directions and it is critical to shade the house from sun from all direction all year round. For a cooling dominant house, minimize windows and openings on east and west facades. This can easily add 1 star to your building.

For a single dwelling, as a rule of thumb, a rectangle shape with long side along north south axis with minimum length for the east and west walls.

For apartments, if there is a corridor with units on one side, a north facing is optimum. If there is a corridor with a row of units on both sides of corridor, surprisingly a larger west/east walls and glazing provides most energy efficient building, provided that all windows has external adjustable awnings or shutters.

At Energy Compliance Consultants, if you are in early stages of design, we can rotate the building and evaluate energy running cost saving and star rating for different orientations and find the optimum orientation and update the architectural design accordingly.

Sitting (considering neighbouring objects around a building)

Neighbouring building, trees and large vegetation can overshadow your house, or funnel winds towards or away from your building and affect your energy rating/assessment.

For a heating dominate house, the house should be sited so that shading from adjacent objects are minimized to the north. The effect of house sitting on the energy efficiency of your house should be considered at the early stages of design.

Note that, in star rating, we only consider heritage listed trees in energy modelling. In VURB and Performance solution modellings, we have the freedom of considering all types of existing objects which is modelled in both Reference and Proposed building.

Zoning and Layout

Zoning is arranging rooms to maximize passive heating and cooling in rooms and building areas that is most needed. This will allow maximizing your star rating before applying any insulation. A good zoning generally means putting living areas in the north and having bedrooms on the south and east side of the building. We tend to sleep better in cooler rooms.

A good layout also allows closing off parts of the house that is not used so they don’t get heated or cooled with mechanical services when they are not needed.

that are used 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.

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.

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).

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.

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.

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.

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.

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.

Involve energy assessor sooner in design process

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.To achieve 6 Star energy rating, a simple approach is to use design criteria that are close to the Reference building that NCC compares you to it.

How to thermally design a more cost-effective 7 star house?

Needless to say, many architects and builders are worried about the additional star associated with this change; they know already how hard it is to build a luxury house with high raked ceilings and highlight windows, 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.

Other relevant articles

• We refer to the wall that separates the Class 1 (residential) building from other class 1 buildings as a “separating wall” in NCC. The wall separating class 1 from any other building class is referred to as “common wall” in NCC. For all other building classes (commercial buildings), we refer to both above walls as “common walls” in NCC.

Amir suggests to change it to :

Note on wall types: For residential buildings, NCC introduces 2 types of walls:

• Separating wall that separates a Class 1 buildings from another Class 1 building
• Common wall that separates a class 1 from any other building class.

For commercial building classes NCC only refers to common wall for both above scenarios.

What are the alternatives to star rating?

There are two alternatives to 6 Star rating: DTS elemental provisions (Deemed to Satisfy method) and Verification Using Reference Building (VURB) method. DTS is similar to a check list for insulation, it is rigid and all its provisions must be followed with no exception. VURB on the other hand, is most flexible energy compliance approach and can incorporate almost any innovative building material and design. 6 Star is a between these two alternative approaches.

DTS or Deemed to Satisfy Elemental provisions method

This is a low cost and fast compliance method. The Deemed to Satisfy (DTS) report provides a list of minimum prescriptive insulation values from National Construction Code (NCC).

DTS compliance is fast (we can do it in a single day), low cost, and simple. However, as DTS 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.

This option is recommended for small and simple buildings with small glazing area.

VURB or Verification Using Reference Building

This is the ultimate energy compliance avenue. It involves modelling your building and comparing its energy demand to a model of your house geometry with NCC Reference Building design criteria and DTS elemental provisions for insulations/glazing.

VURB method has all advantages of the 6 Star rating and eliminates all the cons of 6 Star NatHERS energy rating. VURB allows for more accurate thermal energy modelling of your house. Compared with 6 Star rating, VURB method always result in lower construction costs.

VURB method is highly recommended for high-end houses with large glazing area, high or cathedral ceilings. This option allows for a trade-off between different building fabric insulation and glazing thermal performance to meet NCC Performance Requirements.

Its worth noting that only NatHERS rating can be certified with star rating and other alternatives, VURB and DtS methods get a fail or pass test result. Getting pass in VURB and DtS means the building has achieved 6 Star rating as they are similar tests for the same energy compliance requirements.

NCC 2022 vs NCC 2019 energy efficiency provisions – What to expect?

When NCC 2019 first released, it was obvious that the changes to residential section was little compared with the major changes that was undertaken for the commercial section. Since substantial changes that was made to the energy efficiency provisions for commercial buildings in NCC 2019, for NCC 2022, moderate changes were made to the existing provisions. However, for residential section, it was another story.

Here, we mainly focus on the residential section and the substantial changes made compared to NCC 2019.

Raising the bar for residential energy efficiency provisions

NCC 2019 focused mainly on thermal comfort with 6 star rating satisfying it. However, NCC 2022 is a bit harder on thermal comfort and requires a 7 star which is achievable through use of insulation and glazing with relatively higher performance that was previously required.

In addition to that, an annual energy use budget is required for the building’s services to meet and not exceed. Services here refers to heating system, cooling system, domestic hot water system, lighting and pool and spa pumps. This means sum of energy used by services and an offset by renewables must not exceed an established energy use budget. This method of energy use estimation and compliance is really similar to the old JV3 method as described in NCC 2016, which is now back in NCC 2022 with a new format and this time, for residential buildings. Regarding building services, two options are available to comply with:

Option 1: Annual energy use budget – 70% of Option 2 allowance.

Option 2: Annual energy use budget – moderate allowance.

More on that is described in NCC 2022 Vol 2.0.

NCC 2022 is more inclusive

Class 2 and Class 4 buildings elemental provisions for energy efficiency are covered in NCC 2019 Section J0.2 to J0.5 and mostly covered thermal bridging treatment and provisions related to ceiling fans. With NCC 2022, more detailed elemental provisions are introduced for Class 2 and Class 4 buildings (TBC).

NCC 2022 enhanced verification methods

Satisfying the NCC 2022 Performance Requirements for building fabric doesn’t require modelling of a Reference Building. Heating load limits (HLL) and cooling load limits (CLL) could be calculated independently for each individual building and used as a target for the proposed building heating and cooling demand. This also applies to the Performance Requirements of energy use budget.

NCC 2022 ventilation for tightly sealed buildings

NCC 2019 lacks provisions for buildings that are tightly sealed and only allow fresh air through controlled mechanical ventilation. Apparently in NCC 2022, this shortcoming will be dealt with, allowing for highly sealed houses to be built and avoid unnecessary infiltration while providing fresh air for the occupants (TBC).

NCC 2022 provisions for vapour permeability

Obtaining a 7 star is associated with a high degree of insulation added to the building fabric. This amount of added insulation contributes to the condensation of vapour due to the temperature difference between interior and exterior side of an external wall. For this purpose, new provisions to increase vapour permeability (specially in colder climates) and is introduced in the new NCC 2022 version.

All you need to know about the new 7 Star rating

7 Star is now required under NCC 2022 to satisfy thermal energy efficiency requirements. This used to be 6 Star with previous version of NCC (2019). There are still some allowances for outdoor living area and ceiling fans to reduce star rating requirements in tropical climates (climate zone 1 and 2).

Under NCC 2022, star rating can be used as one way to meet compliance with the thermal performance requirements detailed in Specification 42 (S42C2) of NCC Volume Two (Class 1 buildings) and clauses J3D3 of NCC Volume One (apartments).

Updated climate files and energy star bands: With the new 7 rating, NatHERS 2022 has also updated the climate and weather files from its 2005 version. Along with updating climate files, NatHERS has also updated the energy star bands. Changes in the NatHERS 2022 Star bands are negligible. The new star band is slightly reduced to balance the effect of updated climate files. Comparison of star band and maximum heating and cooling demand for instance for Melbourne is shown in Figure below:

Thermal bridging is included in new 7 Star rating requirement: thermal bridging is a major source of heat loss/gain that was neglected in NCC 2019 for residential buildings. The impact of inclusion of thermal bridging will be major and it will drop star rating by as much as 0.5 stars. For instance, for a typical 4 bed room single storey house with metal-framed floors, walls and ceilings, if thermal bridge is properly considered in NatEHRS modelling, it can reduce star rating by 0.4 stars in Melbourne or Hobart and by 0.5 Stars in Sydney or Adelaide (CSIRO). NCC 2019 had a R0.2 thermal breaks requirement between the frame and the exterior metal cladding to fix thermal bridging in a simple way. The new NCC 2022 requires proper modelling of the thermal bridge effect similar to commercial buildings in NCC 2019.

Whole of Home star rating is a new requirement under NCC2022 that is designed to push housing industry towards net zero houses. In addition to assessing thermal star rating for the building fabric that was done under NCC 2019, the new NCC requires additional star rating called Whole of Home star rating that to assess major fixed energy appliances. This includes lighting, Cooking and plug-in appliances, air conditioning, heat pumps, domestic hot water, pool and spa pump, 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 where using onsite solar PV to offset more heating and cooling demand from building fabric.

The whole of Home rating is separate to 7 star (thermal or building fabric/envelope) rating. The whole of Home rating ranges from 1 (poor) -100 (net zero). NCC 2022 requires 50 Whole of Home rating for apartments and 60 for houses as minimum to achieve compliance. Whole of home rating is now available from all software that are accredited under NCC: HERO Software, BERS Pro and FirstRate5.

The NatHERS Whole of Home assessments, is part of Performance Requirement 2 (PR2) in the NCC 2022.

The Whole of Home star rating demonstrates compliance to NCC 2022 Specification 42 (S42C3) (Class 1 buildings) and clause J3D15 for apartments.

Split heating and cooling check, to meet NCC 2022 requirements, all new houses designs for a given location must check heating and cooling separately and ensure that either the heating or cooling load does not exceed the NCC 2022 limits for that star band and location.

NatHERS in Home thermal assessment

This is a new home energy assessment for existing and established houses that is currently being developed. It is essentially and energy audit and it doesn’t require modelling and building plans. It enables gathering energy use information for the established houses to assign energy star rating and improve its thermal and energy performance. NatHERS In Home assessments are designed for existing homeowners who wish to certify their existing house star rating and disclose it when selling/renting.

All information used in Whole of Home rating, are also gathered for In Home rating. no site visit will be required as information on following will be collected remotely:

• Lighting appliances,
• Cooking and plug-in appliances,
• air conditioning appliances,
• heat pumps,
• domestic hot water,
• pool and spa pumps,
• onsite solar electricity and hot water generation and storage/battery.

What are typical insulation values for a 6 Star house?

A typical insulation values for a typical (200m2) house designed based on the criteria similar to NCC Reference Building are listed below. The following values are extracted from NCC DTS proviosns which is the reference point for 6 Star rating:

How to achieve the 6–star energy rating

https://www.business.qld.gov.au/industries/building-property-development/building-construction/laws-codes-standards/sustainable-housing/energy-equivalence/6-star

How do I increase my energy star rating?

How do I get a 6 Star rating in NSW New South Wales?

How do you get a 8 Star energy rating?

How are star ratings calculated?

Is 3 star a good rating?

How do I get a 6 Star rating in QLD Queenslad?

What do house star rating mean?

How do I get a 6 Star rating in Victoria?

Going beyond 6 star and energy compliance minimums

If your target is beyond the minimum energy compliance standards, and you want to build a house that has minimal heating and cooling energy demand, in this Section we provide some tips to improve your building thermal performance.

We also offer a similar service under passive house modelling where we assist homeowners and architects to quantify the energy cost saving from different energy measures while trying to achieve a cost-effective passive house.