What's the embodied energy? There's more to sustainability than heating and cooling.

Energy efficient houses can significantly reduce heating and cooling energy use and associated greenhouse gas emissions. However, for increasingly efficient buildings, the embodied energy required to produce additional insulation and high-performance glazing can offset operational energy savings and lead to higher overall energy use.

Our study, published in the journal Renewable and Sustainable Energy Reviews, looked at current energy efficiency regulation in Australia. We found that further increasing the energy efficiency level of houses beyond the current minimum requirement does not result in significant energy savings and can even lead to greater energy demands. It is therefore critical that we consider the entire life cycle of a building, beyond just heating and cooling.

Rating Australian homes

In Australia, the NatHERS star-rating scheme is used to provide a measure of the energy efficiency of residential buildings on a scale of one to 10 stars, with 10 being extremely energy efficient and requiring almost zero energy for heating and cooling. The current minimum rating that a house needs to achieve is six stars.

However, achieving a high star rating typically requires more materials – notably insulation, glazing and efficient window frames. These materials require a significant amount of energy in their production, known as embodied energy.

In a climate such as Melbourne’s, a six-star rated home would require less than 114 megajoules of energy per square metre each year for heating and cooling. That’s enough energy to charge 13 smartphones (2016) over a year. In Brisbane, the milder climate results in a lower energy demand for heating and cooling, with a maximum of 43 MJ/m² a year. A new six-star house in Melbourne typically uses two-thirds less energy for heating and cooling than an average home.

Going beyond six stars and towards seven, eight, nine and 10 stars further reduces the heating and cooling demand but requires additional materials for insulation and glazing.

We wanted to find out if the additional embodied energy use of these materials would be worth the heating and cooling savings they offer, as the house becomes increasingly efficient. And the answer is: not always.

Evaluating the overall energy use of energy efficient houses

We used a typical Australian detached house with a fixed floor plan and used two sets of materials to achieve the minimum six star rating in Melbourne and Brisbane, respectively. From this baseline scenario, we investigated increasing energy efficiency through:

  • increasing the insulation level and installing high-performance glazing (improvement by material); and
  • modifying basic design features of the house, for example, exposing a concrete slab on ground for thermal mass (improvement by design).

Through each of these two approaches, we tried to achieve increasing levels of efficiency for the house, both in Melbourne and Brisbane. We also tried a combination of both approaches to obtain a 10-star house in each location. Here is what we found.

Operational energy was modelled using the official Australian dynamic energy simulation software FirstRate 5 while embodied energy was quantified using the most advanced technique globally, called “hybrid analysis”.

Figure 1 compares the total energy use of all investigated scenarios to the baseline scenario, over 50 years, for Melbourne (top) and Brisbane (bottom). The embodied energy associated with extra insulation and high-performance windows is grouped under the thermal embodied energy category. A strong focus on pragmatic and realistic modifications was made. That meant that systems or designs that are not likely to be implemented in an Australian context – insulating the ground floor slab of the garage, triple glazed argon-filled windows, clerestory windows – were not considered. The energy use was measured over 50 years, during which material replacements were factored in and the operational energy level held constant (assuming no deterioration of components or systems). Only fibreglass insulation was used as it is the most common insulation material in Australia.

Figure 1: Difference between the life cycle energy demand of improved scenarios and the baseline houses in Melbourne and Brisbane over 50 years.

Three main observations can be made:

First, additional insulation and glazing are not the solution. In Melbourne, improvements by material yielded almost no benefits beyond the six star baseline rating. In Brisbane, improvements by material actually resulted in a significant increase to the overall energy use, doing exactly the opposite of what the scheme aims to achieve. A nine star house by material in Brisbane can actually use 262 GJ of additional energy over 50 years – enough fuel energy to drive from Adelaide to Darwin (2834 km) 52 times.

Second, improvements by design can reduce both thermal and embodied energy use. As can be observed, improvements by design yielded overall life cycle energy use reductions over 50 years, both in terms of operational and embodied energy use. This is because certain strategies, such as reverse brick veneer walls or exposing the concrete slab either do not require additional embodied energy or actually reduce the total embodied energy demand by using less materials (and not needing to replace them).

Third, the highest star rating does not necessarily result in the lowest overall energy use. As depicted in Figure 1, scenarios combining improvements by material and design achieve the highest possible star rating (10) but do not result in the lowest total energy use across all scenarios.

The current star rating system does not therefore adequately measure the overall energy performance of buildings.

Moving forward

For building energy efficiency regulations to achieve their goal of reducing energy use, they need to consider embodied energy on top of operational energy use. A life cycle approach is needed to ensure that additional operational performance is not offset by additional embodied energy use.

However, this would only be possible and effective by adopting the comprehensive hybrid analysis as a common quantification approach for embodied energy, developing embodied energy (and greenhouse emissions, water and other indicators) databases for construction materials, training professionals in life cycle thinking and raising awareness about embodied environmental effects in general.

In addition, better designs can yield significant life cycle energy savings. Rather than focusing on material and technological improvements, energy efficiency regulations should actively promote better building design as a means to achieve performance. This should be accompanied by better training and education of professionals.

As more stringent operational energy efficiency regulations are imposed, the significance of embodied energy demands will continue to increase and the findings of this study and other similar research will only become more relevant.

Dr Robert Crawford is a senior lecturer in construction and environmental assessment at the University of Melbourne. Dr André Stephan is a postdoctoral research fellow in the Faculty of Architecture, Building and Planning at the University of Melbourne. Christopher Jensen is a lecturer in construction management at the University of Melbourne. Erika Bartak is a tutor in environmental building systems and design at the University of Melbourne.

12 replies on “Higher star ratings for housing don’t necessarily save energy”

  1. The authors’ research highlights the increasing proportional impact of embodied energy on building energy efficiency. Approaching housing energy efficiency with a consideration of embodied energy and a greater emphasis on a design approach to energy performance is a welcome inclusion in addressing energy efficiency for the residential sector.

    For further information on embodied energy in buildings and hybrid analysis, refer to the free Environment Design Guide (EDG) note ‘Life Cycle Energy Analysis’ by Robert Crawford https://bit.ly/EDG71RC

  2. Alex,
    I don’t recall discussing this with Rob.
    We now have many major problems that threaten the credibility of LCA and the Ecolabels and EPD’s that stem from it. Hybrid LCA is just one example, but of even more concern to me is that, through a succession of incremental abuses,the fundamentals of mass/elemental/thermodynamic balance have now become compromised in LCA. These are not little academic niceties of minor significance that we can gloss over – LCA has abandonned its foundation in science to appeal to commercial interests to the point where it is indistinguishable from sophisticated greenwash – anyone can get any answer they want to from LCA. Peer review is not protecting the integrity of the science. LCA has become a branch of marketing rather than a branch of science. The scientific problems are matters of objective proof but few people seem to take them seriously. Nature will folow the truth not our delusions!

  3. You are also likely to come up against the Khazzoom-Brookes paradox, which suggests that energy savings of highly insulated buildings are not properly achieved because users tend to heat and cool more if they believe that the building is efficient. These are wicked problems!

    I’m pleased to see a recognition in the comments of the importance of good basic climate design principles. These are sorely lacking in the current Australian building culture.

  4. The premise “Going beyond six stars and towards seven, eight, nine and 10 stars further reduces the heating and cooling demand but requires additional materials for insulation and glazing” is fatally flawed.

    Taking dwelling designs beyond 6 stars is often achieved with the fundamental application of basic thermal design principals appropriate to the climate zone.

    The 10 Star House Done Dirt Cheap, BDAV 10 Star Challenge award winner in 2012 was reverse engineered to basic volume builder specification for a Melbourne climate with waffle pod slab on ground, brick veneer walls with R2 bulk insulation, Colorbond roof with Insulbreak sarking and R3.5 bulk insulation, and single-glazed timber windows. The lowest NatHERS rating possible with those inclusions was 8.2 Stars.

    Properly informed design decisions are the critical starting point not expensive, high embodied energy material specifications. Once the building fabric is working as well as it can then the size of mechanical equipment and running times can be kept to a minimum.

    This is clearly an instance of a flawed hypothesis leading to the wrong conclusion.

  5. Phillip this “old chestnut” needs to keep getting rolled out until something is done about it. I agree that it’s disappointing to see star rating and thermal performance targeted in this article to highlight the importance of embodied energy. However unless we get Life Cycle Design integrated into building regs we aren’t going to see genuine improvements in environmental performance for a long long time. We don’t have that long so happy to use any technique to get LCD across the line!
    I was guilty of using this same technique myself three years ago:
    Key difference being that we need to target carbon and not energy but that is another story. The main point is that if you aren’t using LCA you are having yourself on when claiming sustainability.
    Nigel and Rob I know you have some issues with agreeing on data but Nigel you said at the end of your post that you would have reached the same conclusion just a bit moderated. Would be good for everyone if the LCA world stopped bashing each other and collectively helped show the rest of the world why moving to LCA (even with some internal discrepancies) is a far better choice for assessing sustainability than the incumbent systems.

  6. Thank you to the Fifth Estate for hosting this important discussion. Thank you Ian Cleland for raising the key issue – we live in, build our houses in and should analyse the total system. In fact, all responses to this article raise important issues that must be addressed.

    These types of systems analysis are certainly revealing some uncomfortable truths – see our recent article in the Fifth Estate that discussed BASIX but reveals some important wider issues that must be addressed about rating schemes.

    Analysis of “sustainable” buildings seems to include assumptions of vested interests, partial counting, partial cost benefit analysis and analysis of incomplete systems. For example, counting the all costs and embodied energy (often worst case) of the “sustainable” solutions and ignoring the full costs and embodied energy of the additional services from the grid from “less sustainable” buildings does create strange answers.

    However, as revealed in our article, the logic underpinning star rating schemes also needs some work – how can a 6 star building in Sydney use half the energy of a six star building in Melbourne.

    My systems analysis for Greater Melbourne (when I was a Chief Scientist) revealed that “sustainable” buildings implemented via the planning scheme would provide cost-benefits ranging from 3 to greater than 8. Alan Peers recently published that CBA results for cities rating from about 2 to greater than 9. But the Regulatory Impact process always finds marginal benefits. However, I did establish that the average “star rating” was less than 2 for Melbourne and it was impossible for a CBA analysis to capture the whole of system/society opportunity value of sustainable buildings. We are about to publish a full economic analysis of sustainable buildings which includes some interesting outcomes.

    I hope these articles are a Call to Action for the industry and independent scientists to address this important issue

  7. Disappointing to see this old chestnut rolled out again. It seems this result is driven by some rather implausible methodological choices, yet all that will be remembered is – “don’t lift energy efficiency standards”. Our research has shown that those standards, set in 2009, are well below economically optimal levels, even if we put no value on greenhouse gas abatement but only consider financial questions. They are falling further behind every year, and yet no change is anticipated until 2019, fully 10 years after the last ones were agreed by COAG. Embodied energy is NOT a reason to hold back operational energy performance standards. The two issues are almost entirely independent. Embodied energy depends on material choices, and there are endless combinations of those for any given star rating. Also embodied energy calculations will vary, if done well, from place to place. Practically they offer little guide to consumers or industry. I think there are few operational conclusions from this research other than a general reminder that it’s good to use low energy/low carbon materials where possible.

  8. Thank you for the interesting data and new perspective. I am intrigued by why insulating materials appear to have such high embodied energy but I think it is a side argument to the main debate.

    The ultimate stakeholder is not the builders, it is the homeowner and the wider community. And they pay the whole energy bill, not just the energy associated with thermal performance. What can Melbourne University do to reduce the cost of building energy (and water) efficient buildings and what can you do to reduce the whole energy and water bill and the resultant resource cost to Australia? We need you.


  9. Interesting response Dr Kate Ringvall, and some additional links from you would be appreciated on the rating tools. Tick a box use of any tool is mindless and useless.
    I rather appreciate the work the authors have put into their article as it reflects two very important (poor) trends – designers ignorant of passive solar design (bring back good mid century modern designers I say) and secondly the techno-solutions (argon filled triple glazing etc etc) which are costly to produce and a bane to replace if broken, and often interdependent on other tech solutions working optimally, meaning a fail in one (due to lack of maintenance) impacts on all the others. Houses are dwellings for people, not technicians, and lifestyle choices can render any dwelling operating sub-optimally. A lack of maintenance renders most systems operating poorly.
    One last point – lifetime homes designed with accessibility features for ageing in place will assist the dwelling avoiding costly modifications at a later date, (which may be for the second or third owner, not the first). These features significantly reduce costly later modifications at a later date and the energy spike for deliveries, tradespeople coming and going, new fixtures, waste material disposal and removal of products before they have reached their economic life. True sustainability is being realistic about dwellings and their ownership stories.

  10. The article is making a good point, especially for the Northern NSW/Queensland mild climates for both heating and cooling BUT the study is regrettably flawed by using hybrid LCA.

    Hybrid LCA combines bounded scope process LCA data with unbounded scope I/O or consequential LCA data. The bounded scope data SHOULD be bounded by a deliberate boundary defined pertinent to the goal of the study. Unbounded scope data, is unbounded in physical scope or over time and would consider the impacts of insurance services for the banker that funded the coal mine that extracted the coal to reduce the ore to metal for the coating on the steel.

    As such, contributions from the unbounded scope data are exaggerated in significance compared to the bounded data, scoped specifically around the problem. Hence the hybrid LCA results are meaningless – neither bounded in scope to address the specific question nor unbounded in scope to explore the fullest range of consequences of the choices.

    For a specific question like this with a relatively short range of physical consequence and over time, ONLY bounded scope process LCA data should have been used. This would probably have reached more moderate conclusions – i.e that only in very mild climates for heating and cooling are embodied impacts of similar consequence to operating energy consequences.

  11. Certainly the life cycle cost of residential buildings is important but you’ve glossed over a major flaw of these so called “energy efficiency ” ratings – they’re not creating energy efficient housing?!? BASIX is doing better but the 6star EE rating tool isn’t worth the considerable amount of paper it’s written on. Until the system doesn’t rate a house with an air conditioner and limited solar passive qualities above an energy efficient solar passive design house it doesn’t matter what the lifecycle cost is. Get the rating tool right first then we can talk about the lifecycle costs of increasing energy efficiency.

    1. Kate,

      Could only agree with you.

      SUCH is also about total integration of all systems not just bits of it. If we can build a 8 star rated development for the same price as everyone else is building minimum standard homes. Why would not you?

      There is a need to think of the whole systems because there is more than just building buildings in the energy equation.

      There is also more than just bums on seats, as I call it. Let’s actually consider the people who live in development. They are part of the system.

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