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 energy compliance report/certificate for your building permit application. Nationwide House Energy Rating Scheme (NatHERS) assessment (star rating) is one of the common avenues to satisfy minimum energy efficiency requirements of the National Construction Code (NCC).

Energy rating or NatHERS rating involves using a simple software to model a house in 2D and apply insulation values close to the minimum requirements of the NCC to calculate the amount of heating/cooling your house/apartment demands to stay energy efficient. The energy demand is then converted into a star rating between 0 and 10 stars. If your house/apartment achieves 6 stars or more, then you get an energy compliance certificate.

star rating

At Energy Compliance, we offer all avenues to demonstrate your building compliance under any conditions.

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What do the energy rating stars mean?

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.

 

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:

  • 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.

  • 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.

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

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

What are the PROS and CONS of Star Rating approach?

energy

What are the alternatives to star rating?

Considering the pros and Cons of star 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.

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). 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. This option 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 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.

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). 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. This option 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.

More on Star Rating

What are the steps of NatHERS energy star rating?

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 geometry of the building is modelled in a plan view (two-dimension) and each room is assigned as an individual zone.

Zoning & Assignment

Building fabric & glazing thermal performance, internal gains, condition type, temperature set point and their schedules are assigned to the model.

Star Allocation & Report

The model is run and several iterations may be needed to reach the desired results. Then the stars are generated and the report is ready.

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

The geometry of the building is modelled in a plan view (two-dimension) and each room is assigned as an individual zone.

Building fabric & glazing thermal performance, internal gains, condition type, temperature set point and their schedules are assigned to the model.

The model is run and several iterations may be needed to reach the desired results. Then the stars are generated and the report is ready.

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 star 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.

How much does it cost to get a 6-star energy certificate?

This depends on the size and complexity of the building. Multiple types of windows, cathedral roofs, uneven floor levels, and multiple adjacent shading elements on the building, adds to the complexity of the work. Contact us, and one of our team members will usually respond in less than 1 hour.

Where can you find further information?

If you have further questions about 6-Star or other options for energy compliance of your building, 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 projects

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

See above that Gordon house has also required a VURB Performance Solution! Sometimes, some high-end houses with large glazing to floor rations could be very expensive to build even using the NatHERS 6 star rating. The Last resort in these cases will be Verification Using Defence Building (VURB) under NCC. This is another service that we offer at Energy compliance consultants.

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.

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.

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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.

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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).

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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 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.