Explanation of BASIX and the thermal comfort rating(NatHERS)

BASIX (Building Sustainability Index)

BASIX (Building And Sustainability IndeX) was introduced by the NSW Government in 2004, in order to regulate how new residential dwellings, alterations and additions (including new pools and outdoor spas) are designed.

NSW Government intended to regulate by setting energy and thermal comfort targets for houses, units, townhouses and villas.

BASIX is one of the most robust sustainable planning measures in Australia, delivering equitable and effective water and greenhouse gas reductions exclusively across NSW. Other states in Australia generally apply the BCA requirement of a 6 star NatHERS rating only.

BASIX effectively in some ways deviates from the BCA in some areas and it is setting its own benchmarks.

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How does BASIX work?

BASIX is an online program that is currently accessible to anyone. The tool has three different sections:

  • Water usage
  • Thermal comfort
  • Energy usage

In the first section (water usage), in order for the project to comply with BASIX, it needs to achieve a minimum score of 40%. Data is usually obtained from information found in the architectural drawings. Typically roof areas, garden areas, star rating of fixtures must be quoted, water tank sizes, pools, run offs must be entered and must be accurate as the results and entries are reflected on the BASIX certificate.

The BASIX certificate will be checked for correlation before the occupancy certificate is issued by the local council certifier. In many occasions occupancy certificate is not issued when information supplied for the BASIX certificate is incorrect.

The second section (thermal comfort/NatHERS) is the trickiest as that section refers to the building itself and not the add-on items specified at the other two sections.

BASIX Methods of Calculation

BASIX offers two different options here for its completion. The DIY and the Simulation Method.

The DIY method can be used by a non accredited person however the issues that can arise from doing this section incorrectly can be quite dramatic. In addition as the information that can be entered is not analytical enough; in many cases to compensate for heat losses a more expensive glazing option is specified by the BASIX software.

As this section specifies the very building itself it is absolutely imperative to be done correctly and the safest way to do this is by using the Simulation Method carried out by an accredited building energy efficiency consultant(NatHERS).

Everything from wall colour, wall construction and insulation, to glazing, and overshadowing from adjacent structures are simulated by the use of third generation softwares such as AccuRate, BersPro and FirstRate. ABSA is the accrediting body and has a vigorous CPD program ensuring that all its assessors are up to date with all the latest trends.

This simulation is often referred to as a NatHERS assessment.

The third section (energy usage) in principle is very similar to the first section and all related information must be entered correctly. This section covers all fixtures/appliances that consume energy, such as hot water system, washing machine and dryer, oven and stove and a lot more.

All information selected in the BASIX will be cross referenced by the certifier.

Effectively BASIX, apart from being somewhat an inconvenience to achieve, the benefits derived by doing so are great as the measures specified can make the running of a dwelling a lot cheaper coupled with the right occupier behaviour.

All new dwellings, alterations & additions with a construction value of $50,000 or more. Plus pools and spas with a volume greater than 40kl must submit a BASIX Certificate with their Development Application (DA) or Complying Development Certificate (CDC).

In summary section one is clearly there to save water and sections two and three are there to save on green house gasses/energy/money.

As energy prices increase constantly it is a really good idea to design and test the design by thermally simulating it (NatHERS)  and predicting its heating and cooling loads, and then perhaps allow for PV panels to reduce energy costs even further.

We can provide BASIX certificates for any residential projects in NSW.

Our accredited ABSA assessor can also provide the NatHERS (Nationwide House Energy Rating Scheme Thermal comfort simulation certificates) separately where the client prefers to do their own BASIX Certificate.

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NatHERS – Nationwide House Energy Rating Scheme

As mentioned above the thermal simulation method in BASIX is often referred to as a NatHERS assessment.

NatHERS (Nationwide House Energy Rating Scheme) is a star rating system (out of 10) that rates the energy efficiency of a home, based on its design, by using a ‘measuring tape’ calculation to estimate a home’s potential heating and cooling energy use.

NatHERS helps to make Australian homes more comfortable for their inhabitants and also helps residents to save on energy bills through smarter design choices.

The rating software tools accredited under the Nationwide House Energy Rating Scheme (NatHERS) are AccuRate, BERS Pro and FirstRate 5.

They can be used to assess the thermal performance of the designs of proposed and existing homes and assess the compliance of new home designs with parts of the energy efficiency requirements in the

Building Code of Australia (BCA).

They calculate heat gains and losses through the building envelope every hour over a year in a particular location, to determine how much additional heating and cooling may be required to maintain human thermal comfort. The tools can also be used to evaluate hourly temperatures within the building if it operates without heating or cooling.

NatHERS Tools

The distinction between tools that predict the energy use of a building versus tools that rate the actual energy use is important because it determines how the tools can be used. Predictive tools such as the NatHERS tools, which have standardised building occupant behaviour profiles, may be used for regulatory purposes because they enable a comparison of like with like — they can compare the performance of buildings if they are occupied by people who behave the same way. By eliminating the influence of different occupant behaviours, these tools attempt to predict future performance of new or existing buildings.

The NatHERS tools have been shown to be accurate in predicting energy performance given the standardised behaviour profiles. However, because actual occupancy and behaviour vary from the standardised profile, predictive tools are not always good predictors of actual energy bills.

The actual amount of gas or electricity used for heating and cooling is influenced by the behaviour of the occupants, quality of construction and efficiency of appliances, in addition to the thermal performance of the building.

Rating tools are typically computer based due to the thousands of individual calculations necessary. They are based on a calculation engine developed by the CSIRO that enables the prediction of the performance of a building on an hour by hour basis for a whole year. Included in the engine are regional climate data and the thermal properties of all major materials.

The NatHERS tools can model the complex effects of building mass, roof types and many other factors including levels of insulation, air leakage, window size and performance.

The performance of a building can be described in terms of heating and cooling loads, hours of discomfort or hourly variations of indoor temperatures in different parts of the building.

Star Rating

For regulatory purposes, the assessment is expressed as a star rating between 0 and 10: the more stars, the better the performance. Star bands are set for each specific climate zone to allow fair comparison of buildings across climates.

Star rating scale overview

NatHERS house ratings use computer simulations to determine the potential thermal comfort of Australian homes on a scale of zero to 10 stars. The more stars, the less likely the occupants will need cooling or heating to stay comfortable.

What is rated?

A house can be rated before or after it is built. The rating depends on:

  • the layout of the home
  • the construction of its roof, walls, windows and floor
  • the orientation of windows and shading to the sun’s path and local breezes
  • Loss of insulation due to downlights
  • how well these suit the local climate.

Energy consumption by hot water systems, lights or household appliances is not considered in the rating because these fittings are usually replaced several times during the life of the building.

Typical ratings

Houses built in 1990 averaged about one star on the NatHERS scale. Before the introduction of national energy efficiency regulations for houses in 2003, less than one per cent of Australian houses achieved six stars.

Many well designed houses are now being built rated seven stars or more. Examples are available on the website.