CarbonetiX – Environmental Engineering Climate Change Consultants
Book a Free, No Obligation Consultation
1300 311 763

Download a .pdf of “MEDIA RELEASE - Why Your 5 Star Energy Efficient Home - Isn't ”

Why Your 5 Star Energy Efficient Home - Isn't

For around five years now, new homes built in Victoria have needed to meet 5 star energy efficiency standards when built. For the last two years, when major extensions have been undertaken, the whole house has had to be brought up to a 5 star standard. And from May next year, your home has to be built to a 6 star standard.

Why 5 star ... isn’t

Many years ago, there was a TV advertisement for engine oil that had the saying “Oils ain’t oils”. Unfortunately, the same is true for 5 star homes. This is for two reasons:

  1. The term “5 star energy efficient home” is misleading. A 5 star energy efficiency rating is not actually an energy efficiency rating - it’s a predicted relative thermal efficiency rating. In other words, it’s a rating that says that a 5 star home is predicted to use less energy to heat and cool than a home of the same size, occupied by the same people living the same lifestyle, relative to a 2 star home.

    But homes don’t just use energy for heating and cooling – energy is used for lighting, hot water and similar fixtures in the house, in addition to appliances installed by the occupants. And the rating doesn’t take into account the energy use of the permanent fixtures such as lights, hot water services, and heating and cooling systems. A home can have an excessive number of inefficient lights, for example, and this has no influence on the home energy rating.
  2. A 5 star home is probably not properly insulated or sealed, because it’s time consuming and expensive to do well, and mandatory building quality inspections do not verify the quality of insulation or sealing. So the predicted thermal efficiency rating may not translate into the actual thermal efficiency rating because of poor quality thermal construction.

The proof is in the pudding

There are no published authoritative studies showing the actual energy savings achieved by 5 star homes, and correlating this to the energy usage predicted in the rating software.

There is only an assumption that 5 star homes actually perform to a 5 star thermal standard. For example, the study “Evaluation of the Victorian 5 Star Building Standard1” by ACIL Tasman - prepared for the Department of Sustainability and Environment (DSE) in October 2008 - does not refer to any actual studies of home energy performance. Rather, it refers to another report undertaken for DSE in April 2007 by George Wilkenfield and Associates, “Options to reduce greenhouse emissions from new homes in Victoria through the building approval process.2” This document in turn does not refer to any published studies, but rather relies on modelling of home energy performance.

The University of Adelaide’s Terry Williamson undertook a study which showed no correlation between home actual energy use (based on its bills) and its home energy rating3. Williamson’s findings may be disputed, however the fact is that there is no published evidence that homes with a predicted 5 star thermal performance, actually achieve 5 star thermal performance.

A predicted thermal efficiency rating doesn’t account for all energy use in the house

A 5 star home should use less energy to heat and cool per square metre than a similar 2 star home. But just because it uses less energy to heat or cool, doesn’t mean your new home will use less energy overall. The 5 star provisions don’t cover lighting, or the efficiency of fixtures such as hot water services, heaters and air conditioners.

A new home may be fitted with lots of halogen down-lights, which use large amounts of power in comparison with older homes. Older homes would traditionally have a couple of oyster style fittings in the lounge room, a fluoro tube in the kitchen, and single bulbs in the bed rooms.

A new 5 star home may have ducted heating throughout, whereas older homes may only have one heater in the lounge room. And new homes are generally larger. The bigger the space being heated or cooled, the more energy needed.

And a new 5 star home may be air-conditioned, whereas an older home may have no air conditioning.

Fortunately the Building Code of Australia is now extending its residential building energy performance requirements to go beyond just thermal performance, and with time these changes may be incorporated into the rating software. But as it is now, a 5 star rating is no more than a predicted relative thermal performance rating.

How thermal energy slipped through the gaps

Home energy ratings are undertaken by accredited home energy assessors that use thermal modelling software. In Victoria home energy ratings have to be undertaken using either the First Rate software or NATHERS. Information about the building from the building plans is input into the software, which is designed to assess how good the “passive thermal design” of the house is. That is how well does the house:

  • Capture and reject radiation - letting in winter sun and keeping out summer sun

  • Store warmth or “coolness” in the house through thermal mass

  • Stop the conduction and convention of heat in and out of the building through its floors, walls, windows and roof

  • Stop the movement of air in and out of the building through gaps and cracks

There is no doubt that a 5 star home has better passive thermal design than a house of the same size built without any passive thermal consideration. Good home orientation to manage radiation, insulation and double glazing, thermal mass, and good sealing all reduce energy use.

Unfortunately however, the predicted thermal performance of the home does not necessarily translate into actual thermal performance because of the way the house is built. Specifically the intensions of good design do not necessarily translate into the reality of good quality installation of insulation and ceiling.

Most homes in Australia are insulated with batts. If insulation batts are compressed they are less effective. If they are torn, rather than cut to size, more heat is transferred through the edges. If they are compressed around wiring, the performance will be less. If there are gaps between batts, heat will go through the gap. And unfortunately the relationship is not linear - heat transfer, through a wall with gaps equivalent to 5% of the wall area, will be much greater than 5% more than were there no gaps. In fact, a study done by the US Navy Civil Engineering Laboratory showed that a 5% gap would increase heat loss by around 15% in a stud wall.4

If you have ever put in insulation yourself, you’ll quickly understand that getting it right is hard work. Rockwool batts are uncomfortable to work with. Polyester batts are very hard to cut. In a new building or extension it might fall to the plasterer to put in the insulation. A plasterer doesn’t want to measure and cut batts exactly to size, a plasterer wants to hang plaster as quickly as possible. Batts may in various parts of the building be alternatively torn rather than cut, stuffed in and compressed rather than trimmed exactly to size, or have gaps where batts join end to end or if they have been cut slightly too small.

And unfortunately there is no mandatory inspection by a building surveyor to ensure that insulation is installed properly. When a new home is built, it has to go through four mandatory inspections. The third inspection is the framing inspection. The fourth and last inspection is for practical completion, which is when the house is habitable and can be locked up.

The building surveyor has no opportunity to verify how well the insulation has been installed. He inspects the house frame – before the insulation goes in, then his next inspection is practical completion, after the plaster has gone up, and he has no way of verifying how well the wall insulation has been installed. The inspector may stick his head up into the ceiling to see if insulation is put in, but also is unlikely to crawl into the roof space inspect the quality of ceiling insulation throughout. The chances are, whether in ceilings, walls, or the floors of timber floored homes, that the insulation may have been compressed, torn, or have gaps, all which significantly increase heat transfer through the building fabric. Or, worse yet, there may be no insulation at all installed in walls where it is impossible to inspect.

When the home energy assessor checks in the software that doors and windows are weather stripped this will typically add around half a star to the home energy rating. As with insulation however, properly sealing a home is lot of work. Air Barrier Technologies, a company that specialises in sealing and testing homes, state that “With regards to air infiltration, the calculation engine [used in the home energy rating software] predictions for an average house can be substantially less than is measured in practice.” This can result in the home using more energy to heat or cool than if it were properly sealed.

For a typical new Victorian home, fan pressurisation testing undertaken by Air Barrier Technologies shows that the rate of air infiltration can be around 3 times that predicted by the rating software. Clearly new homes are not being adequately sealed.

What to do if you are building a new home or undertaking an extension

If you are building a new home or undertaking an extension, and you want it to be energy efficient:

  • Remember that the mandatory home energy rating is NOT a home energy rating, it’s a predicted relative thermal performance rating

  • Install efficient lighting and appliances

  • Use common sense. If you are going to install air-conditioners in every room and keep your home at 22 degrees year round your home will use a lot of energy, even if it is built to a 5 star standard

  • Demand a mandatory inspection undertaken by an independent expert assessor of the quality of installation of insulation and home sealing, prior to the plaster going up

  • If you are still unsure about how well the home has been insulated or sealed, make as a condition of payment to your builder validation of how well the house has been sealed and insulated through testing:
    • Air infiltration testing, to validate how well the building is sealed. If the fan pressurisation test shows that the building is not properly sealed (as predicted by the home energy rating), have the builder seal and retest until such point that the building performs as the rating said it would

    • Thermal imaging testing using infrared thermography combined with air infiltration testing to determine the quality of installation of the insulation. Where the infrared images show that insulation is not performing as expected, then have the builder fix and retesting until appropriate quality is achieved

Suggestions for the future

For energy efficiency ratings to be effective, it’s recommended that the Building Commission:

  • Commission independent research to validate whether or not homes with a predicted 5 star thermal performance are actually performing to a 5 star standard. Use this study then to guide any changes that are required to ensure better thermal performance.

  • Require a fifth inspection in the building approvals process to verify proper installation of insulation and sealing.

  • Additionally require validation of the quality of installation of the insulation and sealing via an accredited tester using accredited and calibrated diagnostic tools. Air infiltration testing and infra-red thermography are technologies that can be used. As the industry comes up to speed and there is evidence that homes are being properly sealed and insulated the first time round it may only be necessary to undertake random spot validation checks.

  • Develop a more comprehensive home energy rating that covers the performance of those fixtures that the building owner is unlikely to change, such as lighting fixtures, hot water service, heating and cooling systems.

  • Over recent years energy efficiency provisions have been introduced into the Building Code of Australia. Building inspections have traditionally had a focus on just safety. Building surveyors need to be up-skilled and certified in how to verify compliance with both the Victorian 5 star standards and the national energy efficiency provisions of the building code.

The 5 star rating scheme as it stands now may be misleading, in that home buyers believe a predicted relative thermal performance rating is an actual home energy rating.

For the 5 star rating scheme to come into line with the state government’s White Paper commitment to reducing greenhouse emissions in Victoria by 20% by 2020, we need homes that actually use less energy overall and are not just predicted to be relatively more thermally efficient.

Bruce Rowse, Director, CarbonetiX
October 2010

To arrange an interview, please contact:

Bruce Rowse
Tel 0438 878 311

About Bruce Rowse

Bruce Rowse, B Eng (Mech), MBA, is a member of the Australian Institute of Refrigeration, Air Conditioning and Heating (AIRAH) and the Alternative Technology Association. He is an AIRAH accredited commercial energy auditor and holds a “D” class electrical licence.

Bruce is a Director of CarbonetiX, a company that helps commercial building owners save energy, money and greenhouse gas through energy efficiency measures.

About CarbonetiX

Discover how to reduce carbon emissions in your organisation – read the Carbon Conservation and Energy Efficiency Blog ( CarbonetiX are a climate change solutions company that offer energy efficiency services, carbon footprint services, software to monitor energy use and energy training solutions, to the government, commercial and education industries. Utilising a three-phase approach of Evaluate | Measure | Reduce, CarbonetiX help their customers save energy and achieve significant carbon reduction. Subscribe to our free newsletter, to receive informative articles, energy efficiency tips and updates on regulatory changes in sustainability: and download a FREE SPECIAL REPORT “Saving Energy On Heating And Cooling Whilst Maintaining Office Comfort”. Visit

PO Box 590 Frankston VIC 3199
Tel 1300 311 763
Fax 03 9783 9068

Download a .pdf of “MEDIA RELEASE - Why Your 5 Star Energy Efficient Home - Isn't ”

Go back to Media Releases

1 Department of Sustainability and Environment, ACIL Tasman, October 2008, Evaluation of the Victorian 5 Star Building Standard.

2 Department of Sustainability and Environment, George Wilkenfield and Associates, April 2007, Options to reduce greenhouse emissions from new homes in Victoria through the building approval process.

3 Published Proc. of 35th ANZAScA Conference. W. Osterhaus & J. McIntosh (Eds.) School of Architecture, Victoria University of Wellington, NZ: Australia and New Zealand Architectural Science Association. (2001), Williamson T.J., O’Shea S., Menadue V., School of Architecture, Landscape Architecture and Urban Design, The University of Adelaide, NATHERS: Science and non-science.

4 CR 80.012, Civil Engineering Laboratory, Port Hueneme, CA, Department of the Navy, 1980, A Study of the Effects of Insulation Gaps on Building Heat Losses.

Subscribe to the
CarbonetiX e-Newsletter
CarbonetiX – Subscribe to Energy Efficiency e-Newsletter   +  CarbonetiX – Subscribe to Energy Efficiency e-Newsletter


Share |
CarbonetiX - Read Carbon Conservation and Energy Efficiency Blog
Read Carbon Conservation &
Energy Efficiency Blog
Carbonetix – Calculate Your Computer Carbon Footprint
Calculate Your Computer Carbon Footprint
CarbonetiX – Energy Efficiency Engineering | Climate Change Consultants | Energy Auditors
Learn Energy Efficiency Skills
CarbonetiX - Energy Efficiency Engineers And Energy Auditors In The News
Read our Latest Press Releases
CarbonetiX - Energy Efficiency Engineers and Energy Auditors
Find out more
About Us
CarbonetiX - Listen to Good News Interviews with Environmental Organisations
Listen to
Good News Interviews
CarbonetiX - Connect with Environmental Engineering Company on LinkedIn
Connect with us
on Linkedin
CarbonetiX - Find Environmental Engineering Company on Facebook
Find us on Facebook
CarbonetiX - Member Energy Efficiency Council   CarbonetiX - Technology Partner ECOSmart Electricians

CarbonetiX - We Use 100% GreenPower Accredited Renewable Energy   CarbonetiX - 100% Australian Owned And Operated

| | | | | | | | | | | | |