Thermal Comfort

DIY method

The Do-It-Yourself (DIY) method is a web-based Deemed-to-Satisfy method for completing the Thermal comfort section of BASIX. Any single dwelling (detached, attached or granny flat) can be assessed using the DIY method.

If you choose the DIY method, you will need to:
  • commit to minimum insulation levels; and
  • select glazing and shading to ensure that the estimated heating and cooling loads do not exceed the maximum loads determined by BASIX.

The minimum insulation requirements are based on the National Construction Code (NCC) climate zone for the nominated construction types (floors, walls, ceiling and roof).

The estimated heating and cooling loads are based on the Nationwide House Energy Rating Scheme (NatHERS) climate region, as well as the nominated windows and shading and skylights.

The DIY method can only be used if:

  • the conditioned floor area is not more than 300 square metres
  • the dwelling is either single or double storey
  • the dwelling must not contain open mezzanine area exceeding 25 square metres
  • the dwelling must not contain third level habitable attic room
  • the glazing area is between 10% and 40% of the conditioned floor area
  • there are no more than 40 windows and glazed doors in the dwelling (combining windows of the same orientation is not allowed)
  • the total area of skylights is not more than 3 square metres.

Some of the above criteria such as conditioned floor area, number of storeys and open mezzanine area will be checked against the inputs provided in the Site Details section to determine if you can choose the DIY method.

Some of these criteria will appear as commitments on the BASIX certificate if you choose the DIY method to satisfy the BASIX thermal comfort requirements.

If your dwelling does not contain any conditioned floor areas (based on BASIX definitions) on the ground floor, the ground floor is not regarded as one of the storeys subject to the limitations of the DIY method.

Only certain types of shading are available using the DIY method, and overshadowing can only be counted if it is directly in front of the centre at the base of the glazing.

The Simulation method should be used when at least one of these criteria cannot be met.

Certifying thermal comfort

These pages describe how councils and certifiers can check that the information submitted in the Thermal Comfort section of BASIX using the Simulation Method is valid. Accredited Assessors may also find it useful to understand what documents must be prepared when using Simulation.

>> You can also download this information as a pdf: BASIX Guide: Certifying Thermal Comfort (version 1.2)

For Assessor Certificates prepared using pre-Dec 2014 versions of AccuRate, BERS Pro or FirstRate 5 version 5.1.x, please refer to previous version of the BASIX Guide: Certifying Thermal Comfort (version 1.0)

There are four elements that must be checked by the consent authority at approval stage, and by the certifying authority during construction, to ensure the validity of the assessment:

  1. Development details
  2. Accredited Assessor details
  3. Assessor Certificate details
  4. Heating and cooling loads


If these elements are inconsistent or invalid, then the application should be returned to the proponent to resolve.

This diagram shows the process of completing the Thermal Comfort section of BASIX using the Simulation Method, beginning with the original plans.This diagram shows the process of completing the Thermal Comfort section of BASIX using the Simulation Method, beginning with the original plans.

 

Simulation method

The Simulation method allows for a wider selection of building materials, shading devices and insulation, often reducing the need for improved glazing and other added building costs.

In the Simulation method, you will need to:

To pass the thermal comfort section using this method, the heating and cooling loads must be below the maximum loads (as calculated by BASIX based on your climate zone).

The Simulation method is not available for alterations and additions except in special circumstances. Please refer to the guide on using Simulation for alterations and additions.

Thermal comfort protocol

The BASIX thermal comfort protocol applies to the Simulation method of thermal comfort assessment. It establishes requirements for:

  • accreditation of organisations that may accredit assessors to conduct simulations, and the accreditation of assessors by such organisations
  • software that can be used by accredited assessors to conduct simulations
  • how simulations are to be conducted by accredited assessors.

The BASIX thermal comfort protocol refers extensively to the requirements in the NatHERS technical notes. It also establishes the hierarchy of interpreting the requirements in conjunction with the NatHERS technical notes. Where there are differences between the protocol and the NatHERS technical notes, protocol requirements prevail.

The current thermal comfort protocol (dated 27/11/2020).

Thermal comfort protocol (dated 01/05/2016) – applicable to BASIX certificates lodged before July 2017.

Note: The 27/11/2020 revision to the thermal comfort protocol allows ceiling fans to be included in thermal simulations.

Roof space ventilation

Roof space ventilation can reduce the cooling load of your dwelling by allowing hot air and excess moisture in the roofspace to escape.

BASIX recognises two types of roof space ventilation which must be installed in accordance with the following requirements:

Gable-end vents

  • Gable-ends are the triangular part of a wall adjacent to the roofspace in a pitched roof.
  • This option will require a minimum of two vents, one at each end of the roofspace, with an aggregate fixed open area of not less than 1% of the ceiling area.

Wind-driven ventilators (whirligigs)

  • This option will require one ventilator for every 100 m² of ceiling (or part thereof), and eave or gable-end vents with an aggregate fixed open area of not less than 0.2% of the ceiling area.

Common areas

Conditioned common areas are not presently assessed by the BASIX Thermal Comfort Index as they cannot be modelled with current approved Software Tools. It is anticipated that Common areas will be assessed for thermal performance in the future.

New or altered construction

If you are installing any new or altered construction then select 'Yes' for the relevant question.

What is a new or altered floor?

Diagram showing a renovation with a new or altered floor indicating that only a new/altered floor needs to be described Diagram showing a new or altered floor 

 

What is a new or altered wall?

Means the wall is entirely new; or, the alteration involves new framing members; or the alteration reveals existing framing members in which no insulation exists.

  • If the work involves entirely new walls then select ‘Yes’. For altered construction, use the clarification below to determine whether your wall is considered altered construction. 
  • If the wall already has insulation under the lining, select 'No'. 
  • If you are unsure whether there is any insulation, select Yes or No based on the advice below and the Certificate will not require insulation if you uncover it during construction. 
  • External walls and internal walls shared with garage – if removing internal lining (e.g. plasterboard) or external lining (eg weatherboards) to reveal framing, select Yes. 
  • If the lining is over new battens, select Yes. You will need to insulate over or between the new battens. If repainting or directly fixing sheeting over the wall or rendering over existing lining, select 'No'. 

What is a new or altered ceiling (with roof above?)

Means the ceiling with roof above means the ceiling with roof above is new; or, the internal and external linings are replaced.

  • If the work involves entirely new ceilings with roof above then select 'Yes'.
  • For altered construction, use the clarification below to determine whether your wall is considered altered construction. If the ceiling and roof already has insulation under the lining, select 'No'. If the ceiling has insulation and the roof doesn't or vice versa, select Yes and the BASIX Certificate will not require you to insulate where you already have insulation.
  • If you are unsure whether there is any insulation, select Yes or No based on the advice below and the Certificate will not require insulation if you uncover it during construction.

Ceiling with roof above

  • If work involves only internal ceilings with rooms above select 'No'.
  • If only replacing the ceiling lining or only replacing the roof lining (not both), select 'No'.
  • If repainting or repairing over existing lining, select 'No'.
  • If the ceiling lining (e.g. plasterboard) of a ceiling and the roof lining (e.g. tiles) are being replaced, select, 'Yes'.
  • You will be required to insulate the ceiling and roof depending on the colour. 

Diagram showing a new or altered ceilingDiagram showing a new or altered ceiling

 

New work separated from existing dwelling

If the new work is only a room which can be closed off from the existing dwelling with walls, floors, ceilings, windows, glazed doors or opaque doors select Yes. If the new floor area is less than 15m² and the total glass area (window, glazed door, skylight, glazed roof and polycarbonate roof) is less than 20m², lower glazing and/or shading criteria will be set.

Diagram showing new work separated from existing dwellingDiagram showing new work separated from existing dwelling 

Heating and cooling loads

The heating load is the amount of heat energy that would need to be added to a space to maintain the temperature in an acceptable range.

The cooling load is the amount of heat energy that would need to be removed from a space (cooling) to maintain the temperature in an acceptable range.

The heating and cooling loads, or "thermal loads", take into account:

  • the dwelling's construction and insulation; including floors, walls, ceilings and roof; and
  • the dwelling's glazing and skylights; based on size, performance, shading and overshadowing.

Lower thermal loads indicate that, relatively, the dwelling will require less heating and cooling to maintain comfortable conditions. Lower thermal loads do not necessarily correspond to lower electricity usage.

In practice, the heating and cooling loads may be handled by heating or air-conditioning equipment. The efficiency of the equipment and the fuel type is assessed in the Energy section of BASIX. Lower loads will improve your Energy score.

Maximum heating and cooling loads

The maximum heating and cooling loads for the dwelling are calculated by BASIX based on the climate zone.

BASIX Thermal Comfort sets maximum heating loads and cooling loads separately, meaning that good performance in heating or cooling alone will not be undermined by poor performance in the other.

Climate and Weather

Weather refers to the temperature, humidity, precipitation, cloud, sunshine, pressure and wind at a particular place at a point in time. Climate describes patterns of weather that emerge over many years.

BASIX assigns the maximum heating and cooling loads to a dwelling according to the NatHERS climate regions based on postcode. Each region has a set of weather data representative of the climate at that location. The weather data has been chosen to be useful for thermal simulation with suitable daily and seasonal averages and variability.

Additionally, for the insulation requirements in the Do-It-Yourself (DIY) method, the National Construction Code (NCC) Deemed-to-Satisfy climate zones based on Local Government Area are used, with some minor differences. The map is available on the Australian Building Codes Board (ABCB) website. The differences are as follows:

  • The Dorrigo region (postcode 2453), being on top of the plateau, is in climate zone 7 (cool temperate) and not climate zone 2 (warm humid/coastal) as indicated.
  • For clarity and simplicity, Perisher/Smiggins (postcode 2624), Thredbo (postcode 2625) and Numbla Vale (2628) are in climate zone 8 (Alpine).

Design principles

BASIX encourages you to choose a design that is appropriate to the climate that the dwelling will be located in (which is also referred to as passive design principles). This includes:

  • Orientation - balancing solar access for winter warming (if required) while avoiding overheating in summer;
  • Windows - balancing heat, light, ventilation and views;
  • Ventilation - managing cooling breezes and reducing uncontrolled air leakage;
  • Insulation - reducing uncontrolled heat gain and loss through the building fabric;
  • Thermal mass - stabilising internal temperatures especially when there is a large diurnal range; and
  • Shading- balancing heat, light and glare.

Thermal comfort

The Thermal comfort section of BASIX aims to:

  • ensure thermal comfort for a dwelling's occupants, appropriate to the climate and season;
  • reduce greenhouse gas emissions from artificial cooling and heating through good building design and use of appropriate construction materials; and
  • reduce the demand for new, or upgraded, energy infrastructure by managing peak demand for energy required for cooling and heating.

The loads from Thermal comfort are combined with the selected heating and cooling appliances in the Energy section to calculate the cooling and heating component of your Energy score. Lower loads will improve your Energy score. In cold or hot climates, you may find this is an effective way of obtaining a Pass in Energy.

Thermal comfort methods

To complete the Thermal comfort section of BASIX, you will need to select one of the following methods:

  • Do-It-Yourself (DIY) method - simplified assessment for single dwelling houses that use common construction materials and methods
  • Simulation method - detailed assessment that uses National House Energy Rating Scheme (NatHERS) accredited software, and can simulate a larger range of construction methods and materials, more complex designs and multi-dwelling developments such as townhouses and apartments.
  • Large boarding house – This method can only be used for boarding houses that meet all the criteria below:
    • it must be designed to accommodate more than 12 people, or the total floor area must exceed 300 m2
    • at least 80% of the dwellings must be less than 35 m2, and
    • it may only comprise residential flat buildings.

If the boarding house doesn’t meet all these criteria, but does contain dwellings of less than 35 m2, you may apply for an alternative assessment as a large boarding house.

  • Passive House standard method – This method only applies to single dwelling houses designed and constructed in accordance with the Passive House standard. You need to engage a Certified Passive House Designer to enter the building design information into the Passive House Planning Package (PHPP) software.


The DIY and Simulation method are broadly equivalent across a large sample of dwellings. However, design and compliance outcomes are likely to be different. This is because the DIY method estimates the heating and cooling loads, whereas the Simulation method calculates the loads using thermal simulation software.

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