Thermal Performance Assessment | Bay Vista

Building Design & Drafting

Thermal Performance Assessment


Is a calculation of the heating and cooling loads required to maintain a comfortable indoor living temperature, with minimal help from heaters or air-conditioners. Only a trained and accredited assessor can certify a home with a 6 Star Energy Rating. All new homes, extensions and relocated houses in Victoria require a 6 star Thermal Performance Assessment under the energy efficiency measures of the National Construction Code of Australia (N.C.C). Specialized software is used to assess a dwelling’s design, taking into consideration the buildings size, wall materials, roof construction, floor construction, window style, glazing, insulation, climate zone and orientation of the building.


What you need to provide for a Thermal Performance Assessment?

A complete set of plans is required preferably in PDF format or hard copy, including:

  • Site plan
  • Floor plan/s
  • Elevations
  • Sections
  • Window sizes or Schedule
  • Artificial lighting plan
  • Ceiling exhaust fans and ceiling fans must also be nominated on the plans.


What do the stars ratings mean?

The stars are a rating out of 10. The current regulation for Victoria is a minimum of 6 stars which indicates a good level of thermal performance and reduced energy bills. 10 stars is the maximum and means no artificial cooling or heating will be required to maintain a comfortable living environment all year round.


What building work needs to meet a 6 Star Standard?

All new homes, extensions and relocated houses in Victoria require a 6 star Thermal Performance Assessment under the energy efficiency measures of the National Construction Code of Australia (NCC). The standard includes lighting efficiency but not plug in appliances. Small works that do not require a building permit may not be affected by the regulations, which commenced on the 1st May 2011.


Do I need to have a rainwater tank or solar hot water system installed?

Only for a new house (renovations and extensions are exempt). Installation of a solar hot water system or a rainwater tank for toilet flushing is required. Details must be supplied when applying for the building permit.


If I am renovating or extending will I need to bring my entire home up to the 6 Star standard?

Any extension or alteration requiring a building permit requires an energy assessment. In Victoria, if the renovation is less than 50% of the original volume of the building, then only the new section will need to be rated 6 stars. If the renovation exceeds 50% of the existing volume then the entire building will require a 6 star energy rating.


What if the design options to reach 6 Star are technically difficult or cost excessive?

Building surveyors can use their discretion to allow partial compliance in certain circumstances, where it would cause ‘excessive hardship’ compared to the resulting benefit or if it were technically not possible. For example if compliance can only be achieved by the insulation of existing external walls, the building surveyor may  grant an exception and approve the plans without insulation in the old walls.


What will this mean when I apply for a building permit?

You will be required to submit an Energy Rating Report prepared by an Accredited Assessor in order to obtain a building permit. Your Building Surveyor will be responsible for reviewing plans to ensure your home, renovation or relocation complies with the 6 Star standards.


At what stage is it best to get an energy rating?

Once you are happy with the plans and they are close to being finalised. This means that the energy assessment isn’t constantly being changed whenever an amendment to the house plans is made. If the design is likely to experience difficulty in achieving a 6-Star rating or a higher star rating is being sort, it is a good idea to involve us earlier in the design phase to conduct a preliminary assessment.


How long will it take?

You should allow 2-3 days for a single storey and slightly longer for a double storey residence.


Design considerations:

Energy efficiency or thermal performance has become a key factor in the design stage of any home. Consideration of energy efficiency when designing your home can produce the following benefits:

  • Lower Construction Costs: With a 6 star energy rating being required for all new homes in Victoria, taking energy efficiency into account at the design stage is a far more cost effective option compared to adopting energy efficiency measures once construction is completed.
  • Lower Energy Bills: An energy efficient home requires substantially less power to maintain a comfortable living environment, thus greatly decreasing energy bills.
  • Year Round Comfortable Living Conditions: An energy efficient home is cooler in summer and warmer in winter, maintain comfortable living conditions with minimal cost.
  • Environmentally Friendly: Less energy consumption means less greenhouse gasses protecting the environment for future generations.


Some key factors to take into account when designing your home are: 


Solar orientation: When deciding upon the layout of your new home orientation should be taken into consideration. Living areas and major windows should face north to maximise the sun’s energy to heat your home. Utility areas should be located to the west to limit the harsh afternoon sun’s impact on your living spaces in summer. Bedrooms should be located to the south or east.


Window location, size and protection: windows should be located so as to maximise winter heat gain from the sun and should be sized appropriately to minimise internal heat loss. Windows should be protected against summer heat by external shading devices (adjustable shading devices are highly recommended when designing a home in Victoria).


Thermal mass: This is best described as using dense construction materials (such as bricks, concrete and compacted earth products) to store heat from the sun, which is later released. In summer, materials with a high thermal mass absorb heat from the atmosphere maintaining a comfortable internal temperature which later at night is then released into the cool breeze (natural ventilation). In winter materials with a high thermal mass absorb heat from the sun which is slowly released at night into the building. Thermal mass works best where good solar orientation is available.


Air movement: Air Movement should be controlled as it can have both positive and negative impacts upon your home’s internal environment. Air leakage (uncontrolled ventilation or draughts) should be minimised as this can result in significant heat loss. Cross ventilation (controlled ventilation created by opening appropriately located windows) can replace hot air trapped inside your home replacing it with cool air from outside. Cross ventilation is most effective when you take natural prevailing winds into account when designing your home (most cool summer breezes come from the south in Victoria)


Artificial lighting: Lighting can not only use a lot of power increasing energy bills, but can also have negative impacts on  your homes thermal performance due to loss of ceiling insulation with the use of down lights and mechanical exhaust fans. Where possible all down lights and exhaust fans should be sealed to minimise air leakage. Low wattage lights and wall lights should be used to minimise loss of ceiling insulation due to ceiling penetrations.


Over shadowing: Overshadowing can have both positive and negative impacts upon your home’s thermal performance. A good northerly orientation can be undermined by obstruction of the sun to the north, such as other buildings, high fences and large trees. If the obstructions cannot be removed, an appropriate setback should be utilized to minimise overshadowing and maximise solar gain. On the other hand overshadowing can be beneficial in blocking the harsh westerly sun. Planting large trees or erecting shading devices to the west of your home is recommended to help keep it cool in summer.