Beyond Efficiency: 5 Key Ingredients for a Sustainable Home (with DataViz)

by Lindsay Wilson in Housing

What is a sustainable building

Look at the two buildings above.  Both of these buildings are energy efficient homes.  Both are aiming for LEED platinum certification.  But only one is built up to be “the greenest New American Home in history”.  Can you guess which?

Yep.  It’s on the left.  What Lloyd Alter aptly named a ‘polyurethane palace‘.

Is this really the new sustainability?  I don’t think so.  I don’t doubt it has a lot of appeal to a certain type of buyer, but if climate change features highly in your concept of sustainability then I’m afraid it’s back to the drawing board.

Making a home highly energy efficient is an essential part of it being sustainability.  But it’s 2014, and a lot of smart people know a lot about what makes a home seriously sustainable.  Here’s a list of five ingredients I think matter, no doubt it’s incomplete.

1) Efficiency

Over the life of a building the operational energy used to run it generally exceeds the embodied energy used to build it (save the likes of a passive house).  This explains part of why there has been such a push for efficiency in recent years.

If you want a sustainable building then efficiency is the logical place to start.  This means designing for local weather, great insulation, efficient appliances . . . maybe a heat exchanger?

Insulated with a Passivhaus

The graph above explains a bit about how a passive house minimizes heating needs by having a building envelope that is well insulated and air tight.  The fabric first approach of passive houses is great for cold climates in particular.

You can read more about passive houses here.

2) Energy Production

As the cost of residential solar has fallen it has become more and more fashionable (and economic) to have solar panels on the roof.  It’s fast becoming a badge of honor.  Far more trendy than solar hot water ever was.  The 6,700 square feet beast above has 16 kW of them (which kind of suggests it’ll still use a great deal of energy).

Aiming to produce more and more of the energy we use on site is a fascinating trend.  And anyone who cracks cost effective residential storage is going to make a lot of money.

carbon intensity of electricity

The chart above shows the benefits of switching from fossil fuel electricity to low carbon sources.  Whether that electricity production is distributed or centralized is less important for the climate, but the falling cost of solar has really brought home production into this equation.  Other local options like solar hot water, heat pumps and biomass are also in play.

You can read more about electricity emissions here.

3) House Size

This is where it often starts to go a bit wrong with ‘sustainable homes’.  There is little doubt that as countries get wealthier they want bigger homes.  But big and sustainable are unhappy bedfellows.

A bigger home needs more energy to build (embodied energy), more energy to run (use energy), more stuff to fill it (more embodied energy) and is often further from things you need, due to the nature of population density and development.

Average house size in square feet

This chart shows the average house size by country in 2009 (you can click it to expand).  Australia, the US and Canada lead the way with massive houses.  They also lead the way with per capita emissions.  That is not a coincidence.

You can read more about house size here.

4) Location

Where your home is in relation to your work, shopping, friends, schools and other amenities has a huge effect on your whole carbon footprint, not just the energy you use at home.  Being able to walk, cycle or take public transport on a daily basis can slash your footprint.

Spatial Footprints

The chart above shows the spatial distribution of household carbon footprints in and around New York City.  The dark green areas, which include Manhattan, are below 40t CO2e per household while the red sections above 70 t.  This reflects the fact that urbanites tend to drive less, use less energy at home and even buy less physical stuff (particularly furnishings and vehicles).

You can read more about the study here. 

5) Embodied Carbon

The embodied carbon of a product is the carbon footprint of making that product.  Each building material used in the construction of a home has its own carbon footprint.   If you tally up all the embodied carbon in each material used to build a home, plus that of any energy used in the process you can estimate the embodied carbon of a building.

For a new home in the UK that figure might be in the 40-50 t CO2e range.  But UK homes are small.  The average suburban home in Australia, the US or Canada could easily be over 100 t CO2e.

emodied carbonThe chart above is a beginner’s guide to the embodied carbon in building materials, based on the excellent Inventory of Carbon & Energy (ICE) database.  The units are kg CO2/kg of material (the actual data also gives CO2e), but you’ve got to remember the density of products is very different.  So a kilo of timber goes a bit further than a kilo of concrete.

In a typical house build the big sources of emissions are the foundations, floor furnishings, windows and walls.  But the choice of material is central to the outcome.  In the chart above I have the figure of 11.5 kg CO2/kg of virgin Aluminum.  If it’s recycled it drops to 1.7 kg.  The good old straw bale stacks up very well.

You can download the full database here.

Beyond Just Efficiency

Greenhouse gas emissions from residential energy use are 11.5% of total greenhouse gas emissions (IPCC WG3).  So improvement in home energy efficiency and domestic energy supply are tackling a tenth of the problem.  But when you also consider the size, location and embodied carbon of a home it also impacts energy, industry and transport emissions.  A much bigger pie.

A half decent architect could sit down and design a home that meets all five of these criteria in no time at all. Many of them do. But would anyone want to live in it?  I’m guessing not. Designing a genuinely sustainable building that people also want to live in is a real art form.

I never really mentioned the other building in the first picture of this post.  It’s called the Merritt Crossing Affordable Housing project in Oakland.  By all five measures I think it is more sustainable than “the greenest New American Home in history”.

So that’s it then: Efficiency, Energy Production, House Size, Location and Embodied Carbon.  My 5 Key Ingredients for a Sustainable Home.  I’ll admit this list feels a little incomplete for some reason, but I’m all out of DataViz.

Is there anything else you are looking for in a sustainable home?

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  • Peter ritchie

    As usual, Lindsay, another great post. We are on track this year to achieve a net zero consumption of electrical energy (yes, we heat with electricity!). Our modest (1500sq.ft.) ICF constructed home, with its 8kW PV solar system, is proof that energy independence (sort of) is attainable. For anyone interested, check out: https://www.youtube.com/watch?v=TyTCFporCt4.
    If I were to build again, today, it would be with hempcrete which is proven to be actually carbon negative as a building material. Drop me a line if you’ve not heard of hempcrete.

    • Lindsay Wilson

      I’ll give it a look tonight. Got some space in my head for it this time

    • Lindsay Wilson

      On payback . . . what is the cost of avoided electricity. What are you getting for a feed in tariff? Our payback here on a 3.29 kWp should be about 9-10 years I think.

  • GeoffBeacon

    Excellent post

    It is good to see embodied carbon carbon mentioned. Government departments in the UK shy away from the topic.

    Do the figures quoted include the embodied carbon in the roads and other infrastructure required?

    What is the embodied carbon in a typical Passive House? Does the Passiv Haus standard address this?

    Any thought of the disparity between keeping a home of about 250 cubic metres warm and the 2 cubic meters that people occupy?

    P.S. When I checked last the ICE data base was rather hard on the carbon footprint of wood. The argument is one for the economists but it is mentioned here: http://www.nohighbuildings.org.uk/wordpress/?p=30

    P.P.S Has anyone tried building a Passive House using Hempcrete?

    • Lindsay Wilson

      If you ever watched grand designs you will of no doubt seen numerous passive houses with over 100t of concrete (and 5 toilets). I love the passivhaus standard, but no it does let embodied carbon slip through.

      I’m a big fan of heating a person instead of a house.

      The treatment of timber in ICE is an interesting one. The don’t give any credit for sequestration which of itself I can live with. How that squares against other materials is a debate. People often like to abuse the negative numbers for sequestration so its a hard one.

      Hempcrete . . that’s a good question

  • Rick Kargaard

    Couldn’t agree more about the size of our houses. They are unnecessarily big, take too much land and waste valuable resources. The same can be said for most motor vehicles on our roads
    You have to be a little careful in using these figures for embodied energy. For example, more than half of aluminum is recycled at 1/6 of the energy cost. Energy for transportation is a huge consideration. Stone is only low in embodied energy if it is available, in a ready to use form, near the building site, I have found that the cost of a material is a good first indication of its environmental freindliness. The least costly usually has the least energy input.

    • Lindsay Wilson

      Much the same can be said of food to be honest. Low price is generally a sign of low embodied carbon

      • Rick Kargaard

        agreed

  • Bob Ashworth

    I like your point about keeping people warm and not the house. Here in southern Spain, we have the opposite problem in summer. Houses are quite dark and people keep all the shutters closed during the day to keep the heat out. In winter people wear house coats (Remember them?!) during the day, an excellent garment for reducing heating costs!

    As far as design is cornered, is there any benefit in improving internal zoning in houses, to stop heat from warm rooms being lost to cooler parts of the house?

    Also, with reference to embodied carbon, does retrofitting old houses have a lower carbon footprint or is that lost through lower efficiency?

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