A Review of Home Energy Rating in Australia: Policies, Evolution & Effectiveness



School of Architecture, Landscape Architecture & Urban Design

Adelaide University




The design of houses to suite the Australian environment has been a preoccupation from the first day that Europeans set foot on the shores of Botany Bay. During the mid to late 1970s the issue of energy resource use was added to the design criteria. Efforts in Australia to encourage energy-efficient housing as a public policy can be traced to this time and provided an impetus for increased research, development and promotion.  Emphasizing energy savings in the home was an integral part of the first public policy programmes.

Since the late 1980s and early 1990s public policy on energy-efficient housing has been motivated, at least in the rhetoric of Governments, by another concern.  In late 1992 Australia signed the UN Framework Convention on Climate Change and the Council of Australian Governments endorsed a National Greenhouse Response Strategy. As one response action of this strategy the Australian and New Zealand Minerals and Energy Council agreed to the development of a Nationwide House Energy Rating Scheme (NatHERS) and to examine the adoption of energy performance standards for new houses. To date, NatHERS has not been adopted throughout Australia, yet in some jurisdictions, notably in areas of New South Wales and the ACT, a NatHERS (or NatHERS based) assessment is mandatory for new houses. Current proposals are to include energy efficiency provisions in the Building Code of Australia (BCA).

This paper traces the history of the development of NatHERS and its implementation. The paper will deal critically with the shortcomings of NatHERS. Referring to limited research data, the fundamental objectives to reduce household energy consumption and reduce greenhouse gas emission are questioned.



Since World War II three periods of research into the thermal performance of houses can be identified. In Australia as elsewhere, a particular issue of concern characterizes each of these periods. The first period 1945-1972 was concerned with discovering conditions for thermal comfort and convenience. The second, prompted by the first Arab oil embargo of October 1972 saw the focus turn to energy conservation and then later to energy efficiency. The final period can be seen to begin with the Rio Declaration on the Environment when the issues of ecological design and sustainable development come to the fore. Public policy on the thermal performance design of dwellings also mirrors these three periods. This paper deals with the third period of thermal performance development and related public policy, particularly the development of the Nationwide Home Energy Rating Scheme (NatHERS).

Policy Directions: Energy, Greenhouse & Global Warming

The beginning of this period has its roots in the 1987 World Commission on Environment and Development a report entitled Our Common Future, known also as the ‘Brundtland Report’ (WCED, 1987).). This Report made it clear that the world's current pattern of economic growth was not sustainable on ecological grounds and that a new type of development is required to meet foreseeable human needs. Sustainable development in this case was defined as,

“Development that meets the needs of the present without compromising the ability of future generations to meet their own needs.”

This report suggested that sustainable development means adopting lifestyles within the planet's ecological means. Publication of the Brundtland Report set in motion a process that culminated in the United Nations Conference on Environment and Development (UNCED), held at Rio de Janeiro in 1992.

The Brundtland Report saw potential climate change as an issue that threatened sustainable development, and recommended urgent action to increase energy-efficiency and moves towards the use of renewable energy.  Several international conferences were organised aimed at directing attention to the consequences of possible global climate change. In June, 1988 the Toronto Conference, The Changing Atmosphere: Implications for Global Security brought together scientists, policy makers and others to consider ideas for an international response to the issue. This conference concluded with a resolution aimed at reducing CO2 emissions. It stated that ‘governments and industry should reduce CO2 emissions by approximately 20% of 1988 levels by the year 2005’ (Toronto Conference, 1988)

In 1990 two reports were released in Australia which addressed energy use and greenhouse gas issues. The Australian and New Zealand Environment Council (ANZEC) in their Report Towards a National Greenhouse Strategy for Australia recommended,

“adopting the initial global targets recommended by the Toronto Conference…as an interim national goal for planning purposes and subject to review, stabilise carbon dioxide emissions to the 1988 levels, prior to the end of 1997.” (Australian And New Zealand Environment Council, 1990)

One of the actions to reduce CO2 emissions proposed by this report was,

“..referring to the Australian Minerals & Energy Council the need to develop and introduce national energy conservation standards for residential and commercial buildings including appropriate insulation standards..” (Australian And New Zealand Environment Council, 1990)

In June 1990 the AMEC (now ANZMEC) produced a report “Energy and the Greenhouse Effect”. This report avoided a commitment to the Toronto Conference target but reiterated a previous Commonwealth government undertaking to,

 “…. achievable target reductions in greenhouse gas emissions, based on scientific assessment and set in consultation with government, industry and environmental groups.” (Australian and New Zealand Minerals and Energy Council, 1990)

This report stressed the joint role of Commonwealth, State and Territory governments in developing any initiatives, meaning essentially that each State and Territory would do its own thing, but did manage to announce,

“AMEC Ministers have agreed to the development of a system of rating new homes by their energy efficiency….The rating system given to a new home will depend on the use of wall and ceiling insulation, passive solar design, the use of energy efficient space heating and cooling, the use of energy efficient cooking appliances, double glazed windows, appropriate window shading and other relevant factors. The rating system will be developed on a State by State basis, recognising that different regions will require different design features and that the interaction between users’ behaviour, building design and performance is very complex, and recognising the initiatives already in place in some States.

AMEC Ministers will also investigate the development of national energy efficiency standards for new homes” (Australian and New Zealand Minerals and Energy Council, 1990)

In late 1990 and following a resolution of the Second World Climate Change Conference, the UN established an Intergovernmental Negotiation Committee (INC) to develop a Framework Convention on Climate Change. After considerable negotiation the Convention was opened for signature at the “Earth Summit" in Rio de Janeiro in June, 1992. The main objective of this Framework Convention on Climate Change (UNFCCC) was to:

". . . achieve . . . stabilization of the greenhouse gas concentrations in the atmosphere at a level that would prevent dangerous anthropogenic interference with the climate system. Such a level should be achieved within a time­frame sufficient to allow ecosystems to adapt naturally to climate change, to ensure that food production is not threatened and to enable economic development to proceed in a sustainable manner" (UNFCCC, 1992, Article 2)

As a framework treaty, the Convention sets out principles and general commitments but left more specific obligations to later deliberations. The Convention relies on voluntary, that is, not legally binding commitments by the signature countries to take steps to satisfy the objective of the Convention and fulfill its requirements. Australia was one of the first countries to ratify the UN Framework Convention on Climate Change, and it came into effect on 21st March 1994. With Australia signing the Convention in late 1992 the Council of Australian Governments endorsed the National Greenhouse Response Strategy (NGSC).  The goal of this strategy was to,

“..to contribute towards effective global action to limit greenhouse gas emissions and enhance greenhouse gas sinks; to improve knowledge and understanding of the enhanced greenhouse effect; and to prepare for potential impacts of climate change in Australia.”  (N.G.S.C., 1992)

The NGSC softened the "Toronto target" as stated in the earlier 1990 ANZEC statement and added conditional requirements,

“..to stabilise greenhouse gas emissions (not controlled by the Montreal Protocol on Substances that Deplete the Ozone Layer) based on 1988 levels, by the year 2000 and to reduce these emissions by 20% by the year 2005…. Subject to Australia not implementing response measures that would have adverse economic impacts….”  (N.G.S.C., 1992 p8)

One objective in this strategy directed at household energy use aimed to,

“improve the energy efficiency of residential buildings and domestic appliances.” (N.G.S.C, 1992 p20)

A related response strategy was that Governments, through ANZMEC (Australian and New Zealand Minerals and Energy Council), expanded on the 1990 statement and again agreed to,

“….expedite the development of a consistent nationwide House Energy Rating Scheme (NatHERS) for trial in early 1994. This project will also examine the adoption of complementary energy performance standards for new houses by the end of 1994, taking into account costs and benefits.” (N.G.S.C, 1992 p21)

In March 1995, and just prior to the first Conference of Parties meeting (COP1) of the UNFCCC, the Minister for the Environment, Sport and Territories, Senator John Faulkner, issued a statement entitled Greenhouse 21c in which an expanded plan of action for the Greenhouse Response Strategy was announced. This new plan was aimed at achieving “.. environmental and economic objectives in the integrated fashion which is central to ecological sustainable development”. The plan called for the development of new expertise in various areas, including energy-efficient building, materials and techniques and reiterates the ANZMEC policy to develop minimum energy performance standards for buildings.

Just prior to the COP3 meeting in Kyoto in November 1997, the Prime Minister made a statement in Parliament entitled Safeguarding the Future:  Australia’s Response to Climate Change. In this Statement, he announced “a comprehensive package of greenhouse response measures”. Included in this statement is yet again the promise to,

“The expansion of the Nationwide House Energy Rating Scheme (NatHERS) by including a minimum energy performance requirement for new housing and extensions to improve energy efficiency and reduce greenhouse gas emissions.”

The statement called for a voluntary approach between States, Territories and key stakeholders, but if after twelve months if there was not acceptable progress, then,

“…[we will work]…to implement mandatory standards through amendment of the Building Code of Australia.”

Also in November 1998, the 1992 National Greenhouse Response Strategy (NGRS) was superseded by a National Greenhouse Strategy (NGS). Again this policy document under the heading of Energy Efficiency Standards for Residential Buildings commits to,

"... develop a minimum energy performance requirement for new houses and major extensions taking into account, as appropriate, opportunities offered by existing performance measures, or ratings, such as the Nationwide House Energy Rating Scheme (NatHERS)." (AGO, 1998)

Australia’s “obligation” having signed the Kyoto Protocol is often now given as the justification for programs to reduce greenhouse gas emissions. Although this is an important goal the reality should be made explicit. The Kyoto Protocol (1997) will only enter into force 90 days after it has been ratified by at least 55 Parties to the Convention, including developed countries and those with economies in transition representing at least 55% of the total of 1990 carbon dioxide emissions from this group. To date 29 countries, mainly island States, have ratified the Protocol. So far no developed country has ratified. Without the ratification of the United States that accounts for 36.1% of carbon dioxide emissions, the European Union for 24.2%, and Russia for 17.4%, the Protocol is unlikely to be “law”, at least in its present form. The current direction of negotiations regarding articles 3.3 and 3.4[1] of the Protocol could mean that human-induced greenhouse gas emissions by industrial type activities have little influence on overall compliance, at least in the first compliance period. The inclusion of unwarranted sinks could in fact create a farcical situation where industrialised countries don't have to make any reductions in their fossil fuel emissions.

The Evolution of NatHERS

The Early Days

A forerunner to NatHERS was the Five Star Design Rating Scheme (FSDRS) which was developed over a three year period (1984 to 1986) by a consortium known as the GMI Council. This group was drawn from industry bodies representing the Glass, Brick (Mass) and Insulation industries. The scheme was officially launched in 1986. Funding of over $750,000 was provided to the GMI Council for the development of the scheme from Commonwealth and State government sources. Prof. John Ballinger from the University of New South Wales, SOLARCH Unit managed the development of the technical basis for the scheme. The scheme was voluntary and set down a pass/fail prescriptive standard that a house design must meet in order to qualify for a FSDRS certificate. Required design features included thermal insulation, northerly orientation of main glass areas, internal mass, window protection and shading. The scheme effectively ceased operation in 1989 due to a lack of industry support. In its years of operation only 40 constructed houses achieved a FSDRS certificate, with around half these being display houses. (SRC Australia Pty Ltd, 1991)

The idea that houses should be required by regulation to conform with certain thermal performance characteristics dates back to the “energy crisis” days of the 1970s. A parliamentary Joint Select Committee on Conservation of Energy Resources first made a recommendation for mandatory thermal insulation of the ceilings and walls of new dwellings in Victoria in May, 1978. The second report of this committee outlined suggested standards for house insulation and also recommended that,

“..the Government, either alone or in conjunction with the State Electricity Commission and the Gas and Fuel Corporation of Victoria, provide moneys to fund an insulation program.” (Conservation of Resources Committee, 1978).

The Victoria Building (Thermal Insulation) Regulations made under the Building Control Act 1981 finally introduced mandatory thermal insulation levels for walls, floors and ceilings for new domestic construction in March, 1991. With the introduction of the Building Code of Australia these Regulations were incorporated into the Victoria Appendix. The performance requirement of the Regulations stated that;

[residential] Buildings shall have a reasonable level of thermal insulation to conserve energy used for heating and cooling the interior of the building. (Thermal Insulation Regulations, Part 54.2.)

Action in Victoria

Once mandatory thermal insulation regulations were introduced in Victoria work commenced on a Home Energy Rating Scheme (HERS). A HERS was seen as an instrument to inform homebuyers of the relative energy efficiency of a house. As such it was considered by many as simply a marketing tool, stimulating consumers to consider the issue of energy efficiency beyond thermal insulation. A Steering Committee comprising representatives of the Victorian energy utilities (SECV and Gas & Fuel Corporation), housing industry, Australian Consumers Association, and Victorian Government’s housing and energy Departments. An initial report by SRC Australia P/L and commissioned by Energy Victoria examined the possible technical basis and implementation strategies for a HERS. (SRC Australia (SRC Australia Pty Ltd, 1992) A crucial part of this study was to recommend an appropriate method of measurement for the proposed HERS. Various “energy efficiency” measures such as end-use operating energy[2], primary operating energy, operating or life-cycle energy costs, CO2 emissions, etc were considered. End-use operating energy per square metre of floor area was chosen as the measure despite admitting that this resulted in certain deficiencies,

“….it does not directly address the issue of life-cycle costing…it is not the best CO2 indicator…it does not address the issue of ‘greenhouse friendly’ fuel selection….” (SRC Australia Pty Ltd, 1992)

Most importantly, yet ignored as a shortcoming, the decision meant that the proposed HERS could not directly address site or primary energy use. Against these shortcomings, the advantages of the measure, it was argued were, that it is relatively easy to calculate, it did not involve trade-off decisions between energy fuel types, and it did not require operating efficiency information or cost data. All the characteristics of heating and cooling equipment were to be ignored along with other appliances such as water heaters.

This Report included a Points Score or checklist type HERS calculation method which allocated a Star rating to an assessed house. Points were allocated to various dwelling characteristics, for example, thermal insulation in ceilings and walls, amount of glass, etc. with the total points determining a Star Rating. The basis for the points scheme were many simulations of a base house model using the CSIRO’s ZSTEP computer program. However, factors such as infiltration, which relies on empirical input data to the simulations, and cross ventilation, which ZSTEP could not deal with at all, were also included in the calculation of the points. The HERS was to comprise a self-scoring procedure directed at a variety of target market groups, including home owners, home buyers, homebuilders, real estate agents, etc.

A further HERS related study for Energy Victoria in March 1992 (Gas & Fuel Corporation & Sustainable Solutions Pty Ltd, 1992) further developed and refined the points score technique. A key recommendation of this report, unrelated to the terms of reference or the investigations described in the study says,

“The point score system should remain based on energy required for heating and cooling, rather than being based on metered energy consumption, energy cost, CO2 produced or other possible bases.” (Gas & Fuel Corporation & Sustainable Solutions Pty Ltd, 1992)

No justification is provided for this recommendation, but its later implications are considerable.

A pilot HERS implementation program was conducted in Geelong during the second half of 1992. This pilot consisted of several parts, including a do-it-yourself rating booklet based on a simplified points score system mailed to 18,000 homes in the Geelong area, and on-site audit assessments of selected homes. This exercise which was essentially the pilot for an energy efficiency marketing campaign, was supported by press and radio advertising and events such a information seminars. In order to easily provide information on the potential impacts of building improvements as part of an audit report, a computer version of the HERS points calculation was quickly developed. This software was a predecessor to the Victorian House Energy Rating software (also known as the VictHERS program).

Discussions on the development of an Australia wide HERS based on the Victorian scheme had begun in early 1992 at meetings of the ANZMEC Energy Management Committee: Buildings Working Group. In a letter to the Chairman of this Group, the South Australian representative wrote,

“[it] is time to agree on a schedule of activities leading to the development of a national HERS…..the most efficient way to do this would seem to be to expand the current Victorian process……[however] three States have been implementing the Five Star Design Rating Scheme…[which] cannot be abandoned, even though it has obvious deficiencies. It is essential that the new HERS be portrayed as a logical extension of the old HERS.” (private correspondence)

Along with the work on the HERS consumer information programme in Victoria, a Residential Building Energy Standard (RBES) was also being considered as an extension of the mandatory thermal insulation regulations. The aim was to develop energy efficient regulations incorporating passive solar design principles, for possible introduction before the end of 1993. (DPUG, 1990)

While the HERS development activity was largely at the Commonwealth and State levels during this period other HERS type schemes were being developed and introduced at Local government level. The Concord Municipal Council in Sydney, for example, with funding from the NSW Department of Arts, Sport, Environment and Territories (DASET) and Pacific Power implemented a Domestic Thermal Assessment Program (DTAP). This scheme developed by Gareth Cole and Associates for Council involved a checklist of building characteristics against which a proposed house design was assessed.

A Meeting of Experts

On the 25th November 1992 a group of 34 ‘experts’ were invited to a meeting in Canberra hosted by the Department of Primary Industries and Energy. The group consisted of Commonwealth, State and local Government representatives, industry stakeholders, and University academics. On the table were several objectives. One ‘to agree on the objectives of a National HERS’ and another ‘to outline the broad requirements of a project (funded through ANZMEC) which would lead to the development of a national HERS meeting the aims of the ANZMEC Ministers’.  The development of NatHERS commenced following a ‘positive’ outcome from this meeting.

An early decision in the development of NatHERS was, following the methodology adopted in Victoria, to limit the assessment to the general performance of the exterior envelope of a dwelling as it relates to heating and cooling loads for an assumed use pattern and a defined climate (Cassell & Ballinger, 1996). An early recommendation was that the rating should be based on a computer simulation of the heating and cooling performance of dwellings and CSIRO was commissioned to provide the software based on the existing ZSTEP program. However, other early decisions, for example that NatHERS adopt the Victorian measure of energy load per sq.m., limited the scheme so that it could not address the broader issues such as performance differences due to the choice of plant or fuel type, embodied energy or life-cycle costs. The question of heating and cooling plant energy efficiency was partitioned off as a separate issue to be dealt with by appliance labeling and associated Minimum Energy Performance Standards (MEPS). Because of these early decisions the NatHERS is not able to provide an assessment of greenhouse gas emissions other than by the implicit assumption that a reduction in energy load will correspond to a reduction in CO2 emissions.

The publicity about the scheme, however, presented a different and somewhat false picture,

“The Nationwide House Energy Rating Scheme (NatHERS) will give houses a rating of up to five stars, according to their design, heating and cooling energy requirements.  The scheme will reduce household energy use and greenhouse gas emissions by providing information on the design and selection of cost-effective energy-efficient housing.”[3]  [my emphasis]

Theory Compared with Reality

The technological view of household energy consumption (and related greenhouse emission) inherent in the NatHERS development is based on the belief that with sufficient accuracy elements of dwelling construction eg. overall U-value, solar penetration, shading, etc. along with an assumed occupant use pattern determine the outcome in a particular climate. Here sufficient accuracy is generally meant to account for differences that result from specific occupant behaviour and local climate variations. But what evidence exists for this belief? Does the real-world data support the moves to mandate thermal performance characteristics of dwellings based on NatHERS? In fact few studies in Australia provide data that can be used to test these questions. Three such studies are examined here, with only one related directly a HERS assessment with actual energy consumption.

The Bonny Rigg Solar Village Experiment

The Bonny Rigg Solar Village was an ambitious project conducted by the Solarch Group of the University of New South Wales, under the direction of John Ballinger. The project, which was opened in February 1982, was conducted in association with the New South Wales Housing Commission and the Energy Authority of NSW. The work involved the construction and instrumentation of 12 ‘passive solar’ designs and 3 standard reference houses. After construction the houses were used unoccupied as ‘test cells’ and opened for display to the public. The dwellings were occupied in August 1982. Monitoring of temperatures and energy consumption continued until the end of 1984. The 1983 energy consumption and comfort data published in Ballinger, et al (1993), together with the detailed house information (Ballinger, Smart, & Shotbolt, 1982) provides a unique opportunity to test the conventional wisdom regarding thermal performance design. Questions that can be asked and investigated with this data are, “What dwelling construction characteristics correlate with a decrease in household and/or heating energy consumption?”, and “Do aspects of house construction lead to increased comfort conditions?”. Using standard statistical analysis techniques the following dependent variables were examined,

·         annual household energy consumption

·         annual heating energy consumption

·         winter and summer daytime comfort conditions (for winter, % of time temperature measured in living room above 18oC, and in summer, % of time temperature below 27oC.)

·         winter and summer nighttime comfort (for winter, % of time temperature above 12oC, and in summer, % of time temperature less than 24oC.)

Independent variables were investigated singly and in combinations and included,

·         overall envelope thermal transmittance, SUA.

·         floor type, timber or concrete.

·         dwelling area.

·         internal mass.

·         area of north facing windows.

The assumption underlying NatHERS (and in particular programs such as VicHERS) is that such relationships exist and are strong.

All but two investigations indicated that the dwelling thermal characteristic were not an indicator of either energy consumption or comfort. Figure 1, for example, shows the relationship between heating energy consumption and overall envelope SU*A. The least squares trend line has a slope opposite to that we might expect and in any case is not significant (R2=0.019, p=0.68).

Figure 1: Annual Heating Energy Consumption vs SUA

Note: One data point outlier(250.3,8507) was removed to create this regression.

Only two statistically significant correlations were discovered from the data. First, the area of north glass was a predictor of the degree of nighttime comfort in winter (R2=0.33, p=0.025) and secondly, the area of north glass was predictor of nighttime discomfort in summer (R2=0.424. p=0.0086). The larger the area of north window the greater the degree of comfort in winter, and the greater the degree of discomfort in summer. This observation undoubtedly has an explanation in terms of solar gains received through the windows.

The NEEHA Project

The NEEHA project (A National Evaluation of Energy Efficient Houses for Australia) was a joint investigation with the SOLARCH group at the University of New South Wales, the Department of Architecture, University of Adelaide, and School of Architecture and Planning, Curtain University of Technology, Western Australia (Ballinger, Samuels, Coldicutt, Williamson, & D'Cruz, 1991). It is probably the most comprehensive investigation of the thermal performance of real dwellings undertaken so far in Australia.

The project was instigated to assess the performance of existing Australian “energy-efficient” houses compared with a sample of “standard” houses. The “energy-efficient” sample consisted mainly of houses about which it was known that claims concerning improved thermal design had been made. The “standard” sample was established from people who responded to newspaper advertisements that sought assistance for a "research project studying the suitability of housing for the climate". In total 146 houses and households in the four city-regions of Australia - Adelaide, Sydney, Melbourne and Perth were studied. Approximately half the houses were “energy-efficient” designs and the other half were houses of “standard” design. The research programme sought to determine whether relationships existed between factors such as user evaluations of thermal comfort, lifestyle, quality/amenity, and both design characteristics and energy consumption.

The data collection techniques used in the NEEHA project included household interviews and a physical design assessment, seasonal questionnaires, and an electronic Environment Response Logger that recorded both indoor climate conditions and allowed input of householder thermal sensations and other factors. Household energy consumption data for the two years prior to the study were obtained from the relevant energy authorities.

From the information collected attempts were made to discover predictors of household energy consumption and comfort from the dwelling construction properties and other characteristics. Note that in this study heating and cooling energy consumption could not be disaggregated from the total and therefore any conclusions related to aspects of thermal performance are on somewhat dangerous ground. The important point however is this: if so much effort is being devoted to the issue of improving dwelling thermal performance, almost to the exclusion of other household energy uses and greenhouse sources, then we might expect to see an effect in terms of total energy use and overall comfort.

Of the hundreds of possible interactions investigated only a few emerged as significant relationships. These are shown in Table 1. Overall the analysis proved somewhat inconclusive, with in several cases, the data showing counter intuitive results that certainly require further investigations. For example, contrary to the expected outcome, bulk thermal insulation was an indictor of higher energy consumption for houses in Melbourne and Sydney. Also in Sydney, higher internal thermal mass was an indictor of a lower level of thermal comfort.

The ACTHERS Review

Mandatory insulation of new framed-construction dwellings was introduced in the Australian Capital Territory (ACT) in December 1992. This meant that for new dwellings, walls and inaccessible roof spaces and floors were required to have a minimum R-value. In late 1995 the ACTHERS rating system was introduced as a supplementary compliance requirement and fully enforced as the requirement for building approval in May 1996. The requirement for the rating of existing housing came into effect at the end of March 1999 through the implementation of the Energy Efficiency Ratings (Sale of Premises) Act 1997 EER(SOP). The ACTHERS rating was calculated using either a detailed checklist rating technique or a computer-based software assessment technique based on the Victorian VicHERS[4] program.

Table 1: NEEHA Evaluations









Nth Orientation





Shallow Plan (E/W axis)





Square Plan





Cross Ventilation





Bulk Insulation in Roof





RFL in Roof





Timber Framed





Brick Cavity





Brick Cavity Insulated





Thermal mass internal





Brick Veneer





Note: Energy: -, probability of using less energy/ +, probability of using more energy

             Comfort: >, Generally recording comfortable conditions on CVL/ <, Generally uncomfortable conditions on CVL.

             Locations shown in Table

A – Adelaide, M – Melbourne, P –Perth, S - Sydney


The tabular (checklist) option was de-recognised in October 1999 and was never accepted for the EER(SOP) ratings. New houses were required initially to meet a minimum of 3 Stars, unless “special circumstances apply”. This was increased to 4 Stars in May 1996.

The stated aims of ACTHERS are to promote energy-efficiency thus leading to a reduction in household energy expenditure and a cut in greenhouse gas emissions.

A review of the ACT House Energy Rating Scheme as it applies to the approval of proposed new housing was commissioned by the ACT Metropolitan Planning and Land Supply Branch (PALM) of the ACT Department of Urban Services in 1998. The Review focused on the success or otherwise of ACTHERS in encouraging the incorporation of energy efficiency measures in housing design and construction. The review was completed in February 2000 (Taylor Oppenheim Architects P/L and Energy Partners, 2000). Issues covered in the review included,

·         comparing the design and construction specifications of houses prior and post the introduction of ACTHERS to determine how new houses achieve the mandatory 4 Star rating.

·         its promotion and acceptance.

The study found that the changes between the pre-ACTHERS and post-ACTHERS[5] house designs included,

·         a mean increase in gross floor area from 147 sq.m. to 156 sq.m. which made it easier to obtain the required star rating,

·         no change in the ratio of north glass area / gross floor,

·         a decrease in overall glass area / gross floor area from 0.24 to 0.21,

·         an increase in mean eaves width on the north (0.40m to 0.44m), the east (0.27m to 0.37m), the west (0.35m to 0.38m) and a reduction on the south (0.67m to 0.37),

·         no change in the percentage of external blinds installed.

In terms of changes to building construction practice between pre-ACTHERS and post-ACTHERS houses the review reported,

·         an increase of floor insulation from R0.14 to R0.33 ,

·         an increase of wall insulation from R1.5 to R1.82,

·         an increase of roof insulation from R0.52 to R3,

·         some double glazing was used (0% to 1%),

·         an increased use of aluminum framed windows from 84% to 88%,

·         increased use of concrete slab-on-ground floors from 78% to 92%,

·         no change to brick veneer being the dominant wall construction method.

A (re)analysis of the household energy consumption data collected during the review of 50 pre-ACTHERS houses and 50 post-ACTHERS houses by this author showed, when wood heating fuel was taken into account (pre-ACTHERS houses are assumed to have wood fueled heaters installed at the 1994 ACT average of 9.3%, (ABS, 1994)), a small 1.9% decrease in total site consumption is observed. Bur because in the post-ACTHERS houses there is an increase in electricity use, the estimated primary energy consumption increased by 0.9%. Likewise when greenhouse gas emissions are calculated, based on the full fuel cycles, the post-ACTHERS sample showed a small increase of 0.2%. Overall on each of these measures there would appear to be little difference between the two samples.

Sampling problems during the Review in matching household energy consumption data and the calculated HERS points meant that an answer to the central question “Does ACTHERS meet its stated aims of increased energy efficiency and reduced greenhouse gas emissions?” was not possible. However, a (re)consideration of the data has revealed a small sample of pre-ACTHERS houses with almost complete data that could be used for such an analysis. This sample of 9 pre-ACTHERS houses had complete electricity and gas fuel consumption over a 12-month period and the ACTHERS points derived from the tabular method. The Review found only small differences between the Points derived from the tabular and software methods. Eight of the sample reported a gas appliance as the main source of heat, while the other reported a solid fuel appliance. In the latter case an allowance was made for using wood as a fuel which contributed to the total household fuel consumption. This was calculated by estimating the gas heating energy per person/GFA and adjusting the total household heat to accord with the person/GFA average. An unknown for this small sample was the actual state of the ceiling insulation, since this was not a question asked during the Review. It was known that at least the mandated insulation required by the 1992 Regulations would be installed but insulation to the accessible ceiling spaces, not required by the Regulations, may also have been included during construction or subsequently added by the householders. A telephone survey by this author of the sample found that in fact most had installed ceiling insulation at the time of construction. The actual state of the ceiling insulation in the year corresponding to the energy consumption data was taken into account in determining the ACTHERS points for each house.

The ACTHERS points (in common with the NatHERS Star Rating) are calculated from an estimation of heating and cooling load, that is the energy that must be added to or extracted from a space to achieve some assumed temperature. The useful heating and cooling energy can be estimated from a dwelling’s actual consumption of gas and electricity for each quarter and summed over a year. The heating/cooling energy is estimated as the excess over the consumption in the minimum quarter. The figures derived by this calculation were checked for apparent consistency by looking at the main heating and cooling appliance(s) use reported in the household surveys. An allowance was made, as explained above, for the one household that reported using a solid fuel (wood) heater as the main heat source. By applying appropriate plant efficiencies the heat added to or extracted from the house was estimated. This “useful” energy or energy load is the basis for the HERS points calculation. Figure 2 shows this estimated load plotted against the ACTHERS points. If ACTHERS was addressing its first objective, within its limitations, we would expect a good correlation to be exhibited between these variables. When the correlation trend line is constrained to pass through zero energy load at 100 points, (corresponding to the ACTHERS assumption that 1 point equals 1% reduction relative to a 3.5 Star house, set at 0 points) the correlation coefficient (R2=0.221, p=0.202) shows a weak relationship between the variables. The null hypothesis (that is there is no relationship) cannot be rejected at the 20% level of significance. In this case the data indicates it cannot be claimed that there is a significant relationship between the ACTHERS points and the actual energy load.

Figure 2: ACTHERS Points vs Household Heating/Cooling Energy Load/GFA

Also shown in Figure 2 is the relationship between the ACTHERS points and the calculated energy load that forms the basis for the allocation of the Star Rating. It shows that ACTHERS overestimates the energy load by some 104%. There is of course a danger that if this figure is used in, for example, cost-effectiveness analysis or in comparing operational and embodied energy, wrong conclusions will be drawn.

In Figure 3 the same ACTHERS points for each house are plotted against the estimated household heating/cooling energy consumption. No significant correlation exists.

Figure 3: ACTHERS Points vs Household Heating/Cooling Energy

As expected the same lack of correlation exists with total household energy consumption shown in Figure 4.

Figure 4: ACTHERS Points vs Total Household Energy Consumption (GJ)

The effectiveness of ACTHERS in achieving its second objective, that of reducing greenhouse gas emission may also be examined. In Figure 5 the estimated full fuel cycle greenhouse gas emission from household heating and cooling operations is compared with the ACTHERS rating points. A correlation coefficient (R2=0.241, p=0.18) shows again that no statistically significant relationship exists.

Figure 5: ACTHERS Points vs Greenhouse Gas Emission for Heating/Cooling



Various statements from the Commonwealth and State governments from the early 1990s have identified the development of a HERS and complementary minimum energy standards for housing as a key policy focus. The twin objectives of this policy direction are defined as increased energy efficiency (particularly for heating and cooling) and reduced greenhouse gas emissions. The development of NatHERS was a response to these policies.

The brief history of the evolution of NatHERS suggests that because of its basic formulation, that is in considering only energy load, it could not, other than by secondary association, achieve its principal objectives. The first technical report prepared by SRC Australia Pty Ltd for Energy Victoria (SRC Australia Pty Ltd, 1992) recognized this fact. Nevertheless the political (or commercial) imperative of avoiding any comparison between fuel types determined the course of the scheme’s development. Designers know however that such partitioning of a problem, because it prevents imaginative tradeoffs being considered, will never lead to truly innovative and holistic solutions. Questions of fuel substitution and the use of renewable energy sources, for example, as well as the embodied energy (and greenhouse emissions) of the construction materials are left totally outside the scheme.

The fundamental assumption inherent in NatHERS, that the calculated energy load for an assumed use pattern relates to energy efficiency has remained a matter of scientific conviction by some and unquestioned trust by others. The belief, however, has never been tested with real-world data. An answer to the simple question “Over a reasonable life-cycle will a house with a better NatHERS rating lead to lower heating/cooling energy use compared to the same house with a lower rating?” remains in the realm of speculation. The investigations presented in this paper are probably the first attempts at such an analysis and the results based on such small samples must be treated with caution at this stage. But the tentative conclusions on the evidence of this data, far from being encouraging, indicate that NatHERS would appear to be fundamentally flawed and will not achieve its stated aims. This conclusion is, however, not peculiar to the Australian HERS. Stein (Stein, 1997) in a detailed study of major House Energy Rating Schemes in the US which do include a consideration of plant type and fuel reported that,

“One of our most surprising discoveries was that none of the HERS we examined showed any clear relationship between rating score and total energy use or energy cost.” (Stein, 1997 p9)

That such schemes could be developed so far without the basic questions being investigated is a damning indictment of the lack of primary research (read research funding) in the area. The bureaucratic processes that measure success, not in terms of basic performance objectives, but rather the number of implementation activities, eg. regulations introduced, assessments issued, etc are also to blame. That the publicity about these schemes suggests they are “best practice” is even more remarkable.

But why, as it appears, do rating schemes get it so wrong when they are based essentially on the science and physics of heat flow? The answer is probably very simple: the real-world variations in the scientific input parameters, for example, assumed R-values, ventilation rates, etc. and factors such as occupancy patterns, heating/cooling systems and their use, etc. swamp the variations that can be explained by science based on “standard” assumptions.[6] And in the case of the NatHERS, not even the science has been fully tested. The NatHERS software (or more correctly the CHENATH simulation engine) developed by CSIRO has been the subject of only limited empirical and inter-program validation (Delsante, 1995a; Delsante, 1995b). Within the limitations of the validation methods the program performed well, but many simulation details remained unevaluated. eg. heat flow to ground, shading, etc. More fundamentally the NatHERS simulation results seem never to have been compared systematically with actual household energy consumption data.

The findings presented in this paper give this author no satisfaction. I believe a way can be found to achieve the notion of sustainability described in the Bruntland Report. However at present we are far from that point and to introduce mandatory energy efficiency building regulations without considerable basic research to demonstrate the real-world effectiveness and value of the scheme would seem premature and potentially counterproductive at this time.

Post Script

The Simpson-Lee house in the Blue Mountains of NSW is lauded by many as an environmentally responsible and sustainable design addressing the many needs of its owners. The building is sensitively located to take in the north-east views and to minimize site disturbance It is detailed to be bush-fire resistant, and it collects and stores water for fire fighting. The building is well insulated and well shaded by the natural vegetation and external shutters/blinds. A large part of the facades are openable to provide an intimate contact with the surroundings and to allow cooling breezes. The only energy consuming heating/cooling devices actually used by the occupants are a single solid fuel fired stove that uses wood from the site and in-slab electric heating that is operated around 2-3 days per month during winter. Temperature monitoring of the building shows that it performs within acceptable limits. When assessed by NatHERS this house is rated at 0 Stars.

Figure 6: Simpson-Lee House by Glenn Murcutt

Photograph V. Soebarto

“It is the trees, it is climate, it is the earth, the water, the rocks, and the landscape which is real. When we fail to see ourselves belonging to and as a part of that we become unreal.”(Glenn Murcutt, quoted in Drew, 1999)

Any energy efficiency scheme that limits design innovation and fails to address sustainability in all its many aspects must also be considered unreal and more significantly, unacceptable.


The assistance of John Ballinger in supplying the Bonny Rigg data and of Trevor Lee, Energy Partners in supplying the ACTHERS review data is gratefully acknowledged.


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[1] Article 3.3 relates to the net changes in greenhouse gas emissions by sources and removals by sinks resulting from direct human-induced land-use change and forestry activities, limited to afforestation, reforestation and deforestation since 1990, and Article 3.4 relates to establishing the level of carbon stocks in 1990.

[2] The term end-use operating energy is a deceptive term. As employed in the report it means the energy load for heating and cooling.

[3]  Quoted from Innovation, No.12, 1995, p.24, a newsletter of CSIRO, Division of Building, Construction and Engineering.  Information attributed to the Commonwealth Department of Primary Industries and Energy, Energy Efficiency Branch, Canberra.

[4] The VicHERS (now FirstRate) software was first introduced in late 1994. It gives a star rating to house designs based on an assessment of the features of the building envelope. The number of stars a design is given is based on a point score system. Point scores are a percentage change in annual energy load compared to a base case. By incrementally varying one element at a time in the base case house a correlation is obtained between say, the level of insulation in a wall and the annual heating and cooling load. The annual heating and cooling load for the many cases were determined using the NatHERS program.

[5] ‘Pre-ACTHERS’ houses were constructed between Dec. 1992 and 1995 inclusive and had installed at least the mandatory thermal insulation.  ‘Post-ACTHERS’ houses were constructed after May 1996.

[6] These exact pitfalls were identified in a report discussed by the ANZMEC, Energy Management Group in 1992 (Williamson and Coldicutt, 1992)