A new home designed to save energy can end up using more than an average house.

By André Stephan and Robert Crawford

25 November 2013 — From The Conversation: Energy efficient houses are often thought to be a promising way to reduce our environmental footprint by using less energy and producing fewer greenhouse gas emissions. Yet, surprisingly, if you consider the whole life cycle of a house, it turns out that sometimes a new home designed to save energy can end up using more than an average house.

Our study, published in the December edition of the journal Applied Energy, found that current building regulations are failing to adequately address the broad scope of energy use associated with buildings. We need to start thinking about building materials, size, location and lifestyles – not just heating and cooling.

Rating Australian homes

In Australia, the star-rating scheme measures the energy efficiency of residential buildings on a scale of 1 to 10 stars, with 10 being extremely energy efficient and requiring very little energy for heating and cooling.

The higher the star-rating, the more materials are typically required – such as for insulation, glazing, efficient window frames – in order to reduce heating and cooling energy demand. All these materials require energy to produce, known as their embodied energy.

In a climate such as Melbourne’s, a 6-star rated home would require 114 megajoules of energy per square metre each year for heating and cooling, which works out to be 27,360 megajoules a year for a typical new 240 sq m house. That’s two-thirds less energy for heating and cooling than an average Melbourne home.

If you go even further and achieve an 8-star rating, that falls to 54 megajoules per sq m – or 12,960 megajoules a year for a 240 sq m house. That’s a good enough result to earn a“passive house” certification in Europe.

However, we found that the additional embodied energy of the materials needed to achieve this improved performance would equate to at least 500,000 to 800,000 megajoules of energy for a new 240 sq m house, even before you moved in. That’s equivalent to the energy you would need to heat and cool the home for 15 to 25 years.

Counting more than energy bills

A house is not just a space to heat or cool: it’s an organised assembly of numerous materials to produce indoor and outdoor spaces. Within these spaces, thermal comfort is required and energy is used to maintain it. Energy is also needed for lighting, appliances, cooking and hot water.

At a larger scale, buildings form neighbourhoods, which in turn form cities. The type and layout of those buildings greatly influence travel distances and the associated energy needed for transport.

Most new houses are built in the outer suburbs of our major cities, often with a lack of reliable public transport services, forcing householders to rely on cars for travelling long distances. This leads to a significant demand for transport-related energy, particularly petrol, especially compared to inner-city households.

The total operational, embodied and transport energy associated with a super insulated house near Brussels, Belgium (equivalent to an 8 to 9-star house in Australia) was compared to the same house built to minimum requirements (6-star equivalent) and an apartment in the city (5-star equivalent).

Four and two occupants were assumed to live in each of the houses and the city apartment, respectively. The occupants of both houses in the suburbs rely on cars for their mobility, while those in the city travel by trams, trains and car.

Figure 1 compares the total energy use of the three buildings over 50 years, per person.

Figure 1: Total energy demand over 50 years for suburban low-energy and standard houses and a city apartment in Brussels, Belgium, by use.

As can be seen above, the total energy use of the passive house (8 to 9-star equivalent) is only marginally less than that of the standard house, and 1.7 times higher than the city apartment.

A closer look shows that the low-energy house requires much more embodied energy than a standard house because of the additional insulation and triple glazed windows it uses. So even though the low-energy house has much lower energy bills for heating (and cooling), that’s offset by a similar increase in embodied energy, negating any benefits offered by the additional materials.

The city apartment results in lower energy use across all categories. This is due to the smaller living space per person, meaning fewer materials and a smaller area to heat and cool. Also, the increased use of public transport greatly reduces transport-related energy demand.

The bigger picture

With all three of our case study homes, more than 50 per cent of the energy demand associated with the house is the embodied energy and energy for transport. What this highlights is that our current energy efficiency schemes and regulations are failing to comprehensively address the broad range of energy demands for building and living in our homes and cities.

In fact, the space heating and cooling demand – which is the focus of most regulations and schemes – represents merely 3 per cent, 9 per cent and 29 per cent of the total energy use for the low-energy house, the standard house and city apartment, respectively.

The current preoccupation with improving energy efficiency for heating and cooling means that the significant indirect energy requirements of houses are often overlooked. This is why we need more comprehensive regulations and schemes that take into account other factors, including house size, the materials used within them, and where they are located.

Trying to reduce our heating and cooling bills is a good start. But there is even greater potential to save energy by considering the materials used to build our homes and the way we move around. Now is the time to look beyond individual homes, and start building better, more affordable, more energy-efficient neighbourhoods and cities.

This article was originally published at The Conversation.
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  1. We are talking about 3 quite different professions/industries: Home energy efficiency (architecture, building and specialist consultants), materials (suppliers, builders) and transport (Planners, Local Government, and State Public Transport). Add to that, the complex layer of what people want to buy when choosing new homes.

    I don’t think it’s fair to say “The current preoccupation with improving energy efficiency for heating and cooling means that the significant indirect energy requirements of houses are often overlooked.”

    People in that field should be concentrating on it, but they have no influence on the availability and feasibility of more sustainable material alternatives, whether houses are being built near public transport or activity centres. Or where the government is investing in new public transport.

    For example, in some cases, new 60 sq m apartments near public transport and activity centres are more expensive than new houses a few km’s down the road. Buyers go for the houses.

    Another example/analogy, ask a government if they would prefer to improve energy efficiency standards or build a new rail line. (I realise I am simplifying the issue).

    Radical change needs to occur, and considering some of the poor energy efficient homes being built, a preoccupation with energy efficiency isn’t stopping the change required.

    It is possible though as can be seen elsewhere around the world.

  2. First of all, the authors are absolutely correct that a whole-of-life approach is needed to make better decisions. The results are not necessarily in line with other studies done in this area, which raises some questions. The structure of the article and especially the graph raises more questions.
    – Location (1): why mix buildings in Brussels with Australian Ratings? The embodied impacts and operational energy requirements (and therefore the LCA results) are location specific. What am I missing?
    – Location (2): comparing urban with suburban buildings is useful when thinking about urban planning questions, e.g.: Should we increase building density? What are the effects of changes in transport modes, building size, embodied impacts, etc. Many of these parameters can be influenced and studied individually. Looking at the graph you could draw the conclusion: we should be building more 5 star city apartments, rather than 8-9 star suburban houses. In reality, this is hardly a trade-off that you’ll come across (i.e. not a useful comparison).
    – Timeframe: The graph shows energy use over 50 years, while the original article talks about 100 years.
    – Occupants: The houses are assumed to have 4 occupants, the apartment 2. This raises questions about comparability.
    – etc… There are numerous other questions, but one issue is critical:
    – Data: Figure 10 in the original article shows a factor 4 difference in “Initial embodied energy of the passive house base case calculated using Australian process and input-output-based hybrid analysis vs. previous studies using European process data”. Given the differences found in embodied energy between the 6 and the 8 star house (500-800GJ), my guess is that Input-Output data have been used… Hence, a factor 4 overestimate of embodied impacts compared to process based LCA studies. The embodied impacts of buidling materials is a quite well understood topic internationally. Even though there is significant variation between countries and between manufacturers, you can get to a very reasonable estimate of embodied GHG impacts (agree with David that embodied energy doesn’t tell you much).

    Finally, I’d like to reiterate David’s point that by using LCA in the design stage you can optimise the house and get a win-win outcome. For a COMPARABLE new energy-efficient home to use more energy than an average home, you’d have to get a lot of things wrong.

  3. Boy oh boy this must have raised the shackles for many green builders (ESD etc)….my self included!
    Articles like this will become urban, or should I say, suburban myths!….”mate, don’t bother trying to live sustainable…its been proved its actually worse……”.
    I know that was not their intention, but I found the article very frustrating – no mention of passive design to achieve higher rating (even the NCC is packed with passive design advise to help designers achieve higher star ratings!). And as David said, why not source the ecologically sound products if you do need to use products. And agreed 240m2 is plain stupid. Also no mention of a very significant source of embodied water and energy, food! Where home owners are composting, collecting rain water and growing food they are making a huge contribution to greening the planet.

  4. It shows how important informed materials selection is if higher standards are to be employed- I can guarantee if materials selection is optimised at design stage with LCA inputs from EPDs or LCA data from schemes such as GreenTag- the picture can change enormously and achieve BOTH ends!

    …BTW I have stopped using EMBODIED ENERGY as a useful term to describe Climate Change impacts given we are finding from our LCA studies that many manufacturers have carbon neutral or low carbon products due to direct renewable energy manufacturing inputs (some even have ‘carbon positive’ products)- i would like to see the study redone to take all this into consideration- happy to work on this if the team is interested..

  5. Interesting article- clearly embodied energy is part of the consideration. Another part which is not mentioned in the article, is the size of the dwelling – the floor area and volume. 240m2 floor area is not a small dwelling by international standards- and this appears to be the floor area of the suburban freestanding examples- but what is the floor area of the city apartment they are compared to? If it’s not 240m2, this clearly is an important contributor to the differential. (and ff it is 240m2 it’s a damn big apartment!)

    1. Ooohh…we’re expecting an interesting response soob to this article, Philip. It’s caused quite some consternation…I think you are on the right track. Be glad for a full response from you too! And any others who would care to. This is such an important topic. Don’t forget Spinifex is for our readers. All yours!