NatHERS star rating

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) assessments is one of the common avenues to satisfy minimum energy efficiency requirements of the National Construction Code (NCC).

What is energy rating or what is NatHERS rating?

Energy rating or NatHERS rating involves using a simple software to model a house in two dimensions and apply insulation values close to the minimum requirements of the National Construction Code to calculate the amount of heating and cooling your house/apartment demands to stay energy efficient. The energy demand of the house is then converted into a star rating between 0 and 10 stars in a standard energy efficiency report. If your house/apartment achieves 6 stars or more, then you get energy compliance certificate and you can use it to apply for the building permit from your local council.

The Housing Industry Association estimates that almost 71 % of residential buildings use star rating as a way to demonstrate energy efficiency compliance [reference].

What do the energy rating stars mean?

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 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 and cooling compared to 5 star houses.

The complete range of star from 0-10 is called star bands. Star bands are based on thermal heating and cooling energy demand for houses in different locations.

Who requires an energy assessment?

Australia’s National Construction Code requires all new buildings and major extensions to satisfy the minimum energy efficiency requirements to allow minimizing greenhouse emissions from the residential sector. If you are planning to build a new building or undertake a major extension, then you will need to obtain a report demonstrating the energy efficiency compliance of your building design to get a building permit. The 6 star certificate is the most common approach for energy compliance.

What building classes need energy rating?

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 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.

A building that doesn’t require a building permit, also doesn’t need to comply with energy efficiency requirements. Read more on NCC building classification here.

Pros and Cons of star rating

Pros:

Energy rating compliance approach is a cost-efficient assessment method for small and medium-sized houses. It is fast to assess the building and it costs less in terms of the assessor’s fee.

Cons:

Star rating compares the annual heating and cooling energy demand to that of a standard 200m2 house. Depending on the conditioned area of the house, if the house is larger or smaller than 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.

What are the alternatives to star rating?

Considering the pros and Cons of 6 star rating, it is worthwhile to consider all other options available for a residential building energy compliance.

These are:

Elemental Provisions or DtS (Deemed to Satisfy method)

This is a low cost and fast 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 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 trade-off between different building fabric insulation and glazing thermal performance to meet NCC Performance Requirements. This option is a more realistic approach in building modelling with all its surrounding features (e.g. shading from a nearby building, etc.) and proved to work even for the most costly-to-construct houses.

At Energy Compliance, we always consider construction cost reduction while minimizing the total energy demand of the house. 

More about energy efficiency rating

When do you need NatHERS energy rating for your residential building

You will need an energy rating or any other option report to demonstrate NCC energy compliance before applying for building permit.

Most of the time, clients approach energy assessor after architectural drawings are finalized. However, we recommend that you consider energy efficiency from the concept design stage so that you can maximize your energy efficiency benefits not by simply adding more insulation but by deciding on building orientation and glazing ratios for different aspects of your building. This approach is guaranteed to help you save in construction costs.

Steps in NatHERS energy rating

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

Modelling: The geometry is modelled in a plan view (two dimension) and each room is assigned as an individual zone.

Material assignment: The wall, roof, floor and glazing materials are assigned to the model. 

Regimes assignment: Different rooms/zones are assigned with occupancy schedule, type of condition, required comfort temperature and internal temperature and humidity gains.

Model run and star allocation: model is run and stars are generated.

At Energy Compliance, we allow for multiple iterations to maximize star rating while minimizing the construction costs. This process will be based on a collaboration between Energy Compliance, Client and the project architect.

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

For a median sized house (approximately 160m2), it will take us 2 to 3 days to finish the energy star rating report.

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

This depends on the nature, 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 any further questions about 6 Star or other options for energy compliance of your next project, refer to the following links or please contact Energy Compliance.

PDF DOWNLOAD – Victorian Building Authority 6 star fact sheet.

PDF DOWNLOAD – Victorian Building Authority Practice Note 55.

NOTE FOR WEBSITE MODELLER: make this available for upload. It is located in upload files folder:

We offer all avenues to energy compliance. Contact us and we will guide to the most cost-effective energy compliance option for your building.

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 VURB rating! 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 to reach 6 star and optimizing a 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. 

Building Code of Australia (BCA) or National Construction Code (NCC) [two name for the same document] recognizes 8 climate zones in Australia. These climate zones vary from hot humid climate (Zone 1) to cold climate (zone 7). 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

Home Orientation: choose a house orientation to take advantage of solar energy. This can inherently add 1 star to your building. For a heating dominant houses, the long face of the house should be aligned to the north. For cooling dominant houses, this factor is of lesser importance as the building receives sunshine majorly from east-facing and west-facing walls.

Internal house layout: for a heating dominant house,spaces used during the day should be arranged to benefit the most from daytime passive heating from the sun.

Thermal mass: maximize thermal mass where solar heat can be absorbed on the north side of the house. There is not much benefit adding thermal mass to areas with limited or no solar access.

Floor: insulate suspended floors or use the insulation effect of the ground by a slab on ground floor option.

Insulation: increase insulation values to more than minimum standard requirements. Glazing is one of the biggest costs in energy efficiency measure and moderate to high insulation levels helps to reduce glazing costs. For instance, increasing insulation on the roof can assist with a major cost-saving by replacing a tripled glazed required by NCC with a double or single glazed window.

Glazing: try to offset heating demand by allowing more solar radiation to the house. Glazing with higher value of solar heat gain coefficient (SHGC) may assist the building in demonstrating compliance with the NCC.

The following strategies are very effective but are not considered in 6 star energy rating.

Deciduous landscape planting to provide summer shade and winter solar gain.

Thermal bridging in building fabric materials to be avoided or minimized.

Passive solar thermal space heating: solar thermal panels work similarly to north-facing windows. It collects heat during the day and stores it in a hot water tank for use during the day and night. Compared to a north-facing window, it has the extra advantage that it doesn’t lose heat and reduce the temperature of the house during the night. Compared with solar PV electricity panels, it can generate up to 5 times more heat. More on that here.

Wind protection: Use of properly planned vegetation to block high speed wind can decrease the unwanted cold air infiltration.

Strategies for cooling dominant houses – warm/hot climate

Thermal mass: minimize in mostly tropical hot humid climates. Maximize in a hot arid climate.

Shading: maximize shading on all east or west-facing windows or use windows with low SHGC. Shading to the northern windows are not recommended for buildings with cold winters.

East/west windows: minimize the surface area, utilize moveable external shading such as tracked shutters. 

Floor: apply less or no insulation to the ground.

Roof: light-coloured, well ventilated or parasol roofs .

The following strategies are very effective but are not considered in 6 star energy rating:

Albedo: Maximise the reflection of solar radiation from external surfaces of the house.

Landscape planting: to control Albedo,channel breezes and benefit from shading.Minimise solar reflection from the landscape and surfaces surrounding the house.

For buildings with refrigerated air conditioning: apply the moderate to high insulation levels, minimize air infiltration and eliminate thermal bridging. This is to keep the cool air inside and avoid mixing it with hot moist outside air.

For a hot arid climate: use evaporative cooling as the most efficient air conditioning solution. Your energy assessor can quantify the number of hours that this solution will be effective per year.

Passive cooling: use innovative solutions to maximise natural ventilation and natural cooling from the ground.

For a hot arid climate: use evaporative cooling as the most efficient air conditioning solution. Your energy assessor can quantify the number of hours that this solution will be effective per year.

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.