The top 10 rules for energy efficient house design – 10

January 4th, 2012

Rule 10 – It takes a bit of energy to make a brick

Digging up the clay, mixing it to the right colour and consistency, moulding it into shape, firing it, cooling it, packing it and delivering it to a building site uses 10.25 MJ or so (about 2.8kW*hr).

Multiply that by the number of bricks in the average Australian masonry house – (According to Austral Bricks, somewhere around 8,000 for brick veneer and 22,000 for cavity brick) – and you’ve burned around 82 GJ and 225 GJ respectively, (or somewhere between 1.7 to 4.7 years of domestic energy usage by that average Australian household).

The energy used to extract, process and deliver that brick (or, for that matter, any other building material) is referred to as its embodied energy, and it’s a significant part of a building’s life cycle energy debt.

Recent research by the CSIRO has found that “the average household contains about 1,000GJ of energy embodied in the materials used in its construction. This is equivalent to about 15 years of normal operational energy use. For a house that lasts 100 years this is over 10% of the energy used in its life”.

Part of the problem with considering embodied energy is that to date it’s been practically invisible. All that energy use happens far away in mines, quarries, refineries, factories and freeways; and it’s notoriously difficult to measure. As a result, like most practically invisible things, it gets ignored.

But that’s about to change with the introduction of the Federal Government’s carbon tax on 1 July 2012.  500 of Australia’s biggest carbon emitters, including electricity generators, cement and steelmakers and other industrial processors, will be required to measure or estimate the carbon emissions associated with their energy use or other greenhouse-gas-producing chemical reactions, and pay a tax per tonne of carbon dioxide equivalent (starting at $23/T). That tax ultimately gets passed on to the end consumers of any product.

The net effect for Australian homebuilders is that embodied energy is going to start getting expensive.

Take our 10.25MJ brick, for example. In Victoria, where electricity is generated using carbon-intensive brown coal (1.4 tonnes of CO2e per MWh) our brick will be responsible for the production of .00392 tonnes of CO2e, and attract 9.016c of carbon tax.

An average Australian house, based on the CSIRO’s estimate of 1000GJ would attract about $8,951.00 carbon tax.

So what do we do to reduce the embodied energy of our buildings?

The obvious answer is to select materials that have a lower embodied energy. Recycled materials generally have a lower embodied energy than those processed from their raw state. Local materials require less embodied energy for transport to your site. Some suppliers make their materials more efficiently than others, and some materials need less processing than others.

There is a catch, though: Some higher thermal mass materials, which reduce operational energy over the life span of your building when used correctly, have high embodied energy. Some high embodied energy materials, like copper or zinc, last for a long time. The long term energy savings need to be balanced against the initial energy costs.

Another sensible approach is to use no more materials than you need. This is another good argument for smaller buildings and less wasteful construction techniques (which might include specifying standard sizes and minimising offcuts).

The kicker? Spread the embodied energy of your materials over a long, useful life. Design buildings that are durable, adaptable, and where valuable and energy-intensive materials can be recovered for reuse. And then don’t tear them apart every few years to suit a change in fashion.

Embodied energy is a curly subject. It’s hard to measure, hard to control, hard to balance against your building’s day-to-day energy use. It sometimes requires your architect, designer or builder to recommend you leave your building alone. Is it any wonder we hear so little about it?

The wonderful image ‘Street Bricks‘ above was posted on Flickr Creative Commons by

* source: Your Home Energy Manual

The top 10 rules for energy efficient house design – 09

June 3rd, 2009

 Rule 9 – Know your Stuff.

When we talk about energy efficient houses, it’s easy to get stuck on the same two topics – heating the house and cooling the house – to the detriment of everything else.

The government legislates that we assess the heating and cooling efficiency of our homes with 5-star ratings. Many of us insulate and seal, judge our sun angles, add our thermal mass and select our glazing thoughtfully.

And that’s really important, when you realise that space heating makes up 38% and space cooling 3% of Australia’s residential energy use (about 161.5 PJ out of 396.6PJ total in 2007).

But it’s really concerning when you wonder where the remaining 59% goes:

23% on heating water…

4% on cooking…

And the last 31%?




124.9 PetaJoules (3,469,444,447 kilowatt hours) per year of …stuff. What the Federal Government’s 2008 report ‘Energy Use in the Australian Residential Sector 2986-2020′ refers to as ‘appliance uses’.

Stuff – it’s everywhere. Doing stuff. Using stuff. In your house. Some of it is important stuff – lighting, refrigeration, clothes washing – but some stuff borders on the pointless. I’ve heard it said that the average microwave oven uses more energy on stand-by over the course of a year than it does cooking food. That’s a lot of energy for a clock that spends way too much time flashing ‘12.00′.

Stuff is weird – or the way it uses energy is at least counter-intuitive. By 2020, it is expected that more power will be used by TVs than lighting in Australia – 45PJ to 25PJ, thanks to the trend towards larger screen LCDs and the proposed phase-out of incandescent lights.

In fact, thanks to improvements in the efficiency of our building envelopes, an increasing percentage of the energy we use will be going towards the appliances whose cables clutter our skirting boards and snake across our floors.

The Australian Federal government has recognised this, and is preparing legislation to improve the energy performance of appliances, including maximum stand-by loads, and a proposed shase out of incandescent light fittings. Many appliance types already have Minimum Energy Performance Standards

But it’s up to us to make sure that the energy we save with our efficient, ’sustainable’ buildings isn’t ultimately wasted on the screens, chargers, transformers and blinky lights we put inside them.

So where do we start? is a good place to begin. Fridges and Freezers, clothes washers and dryers, dishwashers and single phase air conditioners are all required to carry an energy rating label, which shows the comparitive energy usage of the appliance over the course of a test year, and a star rating for a quick, comparative assessment of the appliance’s energy efficiency.

You might also have seen the Energy Star logo from your computer monitor’s start-up screen. Energy Star is an international standard for energy efficient electronic equipment, started by the United States Environmental Protection Agency in 1992 and adopted by several countries in the world, including Australia. Energy Star products, including TVs, VCRs, audio devices, computers, monitors, fax machines and copiers reduce the amount of energy used by either switching the product into a ’sleep’ more when not in use, or reducing the energy used by the appliance when in standby mode. Energy Star estimate that selecting home entertainment or office appliances that are Energy Star enabled can produce energy savings of up to 75% and 50% respectively per appliance.

Of course, the most imortant element of energy efficiency is human behaviour. How and when you use appliances, whether you turn them off at the wall or at the stand-by switch, whether you leave lights burning all night, all the things your parents used to nag you about.

It’s not a particularly sexy aspect of efficient housing, is it? No straw bales, phase change materials or solar panels. But at 31% of your home’s energy usage, it’s important… stuff.

Energy usage statistics from Energy Use in the Australian Residential Sector 2986-2020, Australian Federal Government

Power board photo by unimatrixZxero

The top 10 rules for energy efficient house design – 08

May 12th, 2009

Rule 8 - Every house needs some of these…

Seal photo by mkebaird

I’ve just spent a good part of this morning on the site of one of our alteration-and-addition projects, very close to completion.

The insulation is concealed within the walls, ceiling and floor. The double glazed windows are installed, with frames painted and awaiting a final clean. The low-wattage fluorescent downlights need some final adjustments, but on the whole, the project is tantalisingly close to its final stages.

So it would be really easy to overlook one of the most important energy-efficiency aspects of the whole project – something that, if missed, could compromise all of the other smart technologies and fittings that are installed and ready. Something small, subtle and hard to notice:

The performing seals.

There’s no pool, balancing ball or buckets of fish in this project, but there will be seals everywhere. Seals on the door jambs, head and sill. Seals on the window sashes. The walls are sealed with taped and overlapped wall wrap, and gaps in the existing floors or junctions in material have been sealed with filler.

Air leakage in (infiltration) or out (exfiltration) of buildings is a major source of unwanted heat gain or loss. It is estimated that up to 25% of heating cost in older houses could be saved by limiting air leakage in simple ways.

Typical sources of heat loss include:

  • Fixed wall vents (required by regulation in houses built before 1984).

  • Poorly fitting windows and doors (increase energy cost by up to 15%).

  • Gaps between external doors and windows and door frames, and around construction joints and pipes.

  • Open fire places (five or more air changes per hour increase energy requirements by up to 120%).

  • Vented skylights which allow warm air near the ceiling to escape.

  • Non-sealable exhaust fans.

  • Unsealed duct outlets.

  • Downlights or recessed light fittings which require fixed ventilation to cool the luminaire (adding up to 10% to heating costs).

Source: Energy Smart Housing Manual, Sustainability Victoria

The gap around a poorly-fitting door can be equivalent to having a brick-sized opening in your wall, letting uncomfortably cold or hot air in, every hour of every day.

A good architect or designer should have a fair idea of where the possible paths of air leakage will be in your home, and what strategies to take to deal with them – make sure to ask. But dealing with infiltration and exfiltration is something you can do relatively easily with an existing house – even if you’re renting. Many of the solutions are simple and cheap, and some can be taken from house to house if required.

Windows and doors can be stripped with self-adhesive foams. Draught excluders - from the most complex self-operable seal to the basic bean-filled door snake – can be fitted to the base of doors. Silicon or acrylic fillers can be squirted into most gaps (but please check if the gap is doing something useful first). Self closing ‘top-hats’ can be fitted to some extractor fans, and diffusers to some skylights.

The best part of these very simple modifications is how immediate and noticeable the improvement usually is. It will take a lower setting on a heater to achieve the same level of comfort in winter, and an air conditioner would have to work much less in summer to achieve equivalent or better cooling

Australia is a long way behind the eight-ball when it comes to sealing buildings against air leakage. In parts of Europe and the USA houses are tested for air-tightness before completion with powerful air blowers, and fresh air enters the building through heat exchangers to limit the escape of useful warmth in winter. Our moderate climate and cheap energy has made us complacent, so even our new houses are often very poorly sealed.

It’s a terrible waste, because the solutions are so simple and affordable, and the benefits so marked. Couldn’t your house do with a pet seal or two?

brilliant seal photo posted on Flickr by mikebaird

The top 10 rules for energy efficient house design – 07

May 4th, 2009

Rule 7 – Houses don’t use energy; people do.

Light switch

Paradoxically, one of the biggest mistakes that architects tend to make when designing ‘Eco’, ‘Green’ or ‘Sustainable’ houses is concentrating too hard on the stuff they know.

Seeing themselves as manipulators of form, space and material, they produce artful arrangements of (you guessed it,) form, space and material, full of the coolest technology, and every feature that opens, shuts and whistles. And then wonder where the savings in water and energy went, why the wastewater treatment tanks has gone septic and why the wonderful new building is neither as warm or as cool as it should be.

It shouldn’t be such a surprise. The most powerful design factor that leads to houses that use resources efficiently is not insulation, thermal mass, sun angles or embodied energy, or anything that can be drawn on a plan or scheduled in a specification.

It’s human behaviour.

An operable sunshade is of no use if nobody operates it. The most sophisticated waste sorting system is just waiting to become landfill if nobody uses it. A curtain that nobody closes is a dust collector, and a curtain that nobody opens is a wasted window. 

These technologies should be saving us money, or making our homes more efficient, but they’re just another case of empty consumption unless they fit into the way we live our lives.

Good architecture – and good architects – respond to this in two ways. The first, very difficult, way is to learn about their clients, and design a home around the way they live. This isn’t easy stuff, and involves a lot of searching questions and patient observation during the briefing stage of a project; a lot of to-and-fro with the Client, and some insight on the Client’s behalf. This is vital in all good architecture – whether focused on sustainability or not – and takes time, trust and clear thinking.

The second way, very easy to do badly and extremely hard to do well, is to design a home that begins to shape the behaviour of the people who enjoy it.

Some really, really great architects seem to do this stuff almost intuitively. The great minimalists challenge their clients to live minimally.  The best Regionally responsive architects design places that encourage their occupants to accept the beauty and benefits of the climate they live in, and not feel compelled to shut out their surrounds with air conditioning or plate windows.

My approach? I’ve seen too many arrogant designers come unstuck presuming they could redesign their clients. But I’ve always felt that all of my clients already have the beginnings of an image in their own heads about better ways to live, and how shaping their environment might help shape that.

If that sounds familiar, I’d like to hear from you.


The fantastic image of the light switch above was submitted to Flickr Creative Commons by Rex Roof.

The top 10 rules for energy efficient house design – 06

February 13th, 2009

Rule 6 – Enough is Enough

 Too much of a good thing?

In May 2007, while launching a local architectural competition, the Victorian planning minister Justin Madden made a speech that lit the first spark in a local political firestorm.

We are suffering housing obesity..” he claimed.”..Our increasing affluence has led to bigger houses, and I’m sure that you’re familiar with the term ‘McMansions’….”

He linked the inexorable growth of house sizes to a number of social and environmental ills: Urban sprawl, stretched infrastructure, loss of arable farmland, resource overuse, greenhouse pollution and childhood obesity.

The response was swift, loud and vicious. Within hours the minister had been accused of turning his back on the working class, forgetting the principles of freedom and democracy and spitting on the Australian way of life. Critics included the usual opportunistic soapbox shouters, some special interest groups (including the Housing Industry Association) and some offended homeowners who resented the minister’s criticism of the lifestyles they had worked so hard to achieve. The minister’s own house was scrutinised, and much noise was made about his own five bedrooms and family room and the Victorian Premier’s holiday house.

Within a week of the speech, The Honourable Minister for Planning had deeply qualified his statement and retracted to lick his wounds. An important lesson had been learned: You don’t knock the Australian Dream without risking a kick in the guts.

So what could I possibly add to this debate?

The economic and ecological advantages of a smaller house are pretty straightforward. Smaller houses need less stuff to make. Fewer things need to be dug out of the ground, cut out of the forest, synthesised, processed, transported, packaged and installed to make a smaller house. All other things being equal, smaller houses require less energy to heat, cool or light.

Smaller lot sizes swallow less arable land. More people can be serviced by every kilometre of cable, pipe, road or rail. Trips are shorter, transport is easier, and it becomes easier to ride or walk to where you need to go – and more economical for business or government to provide you with what you want locally. There are fewer transmission losses from electricity, fewer leaks from plumbing, and less energy required to pump, reticulate or deliver the basic infrastructure deliverables.

So how do we resolve that with our lovely big backyards with spreading trees and lawns for backyard cricket, our two-car garages, our rumpus rooms, parent’s retreats and home workshops?

There’s a great line attributed to William Morris that goes: “Have nothing in your home that you do not know to be useful or believe to be beautiful”. Morris supposedly said that in 1880, and yet it’s one of the best pieces of advice for sustainable living in the 21st century that I can think of.

Everything in your home – every room, space, fitting or material should be working hard for you, improving your life or giving you pleasure, serving a purpose, giving you joy or ideally all of the above. If it’s not useful, and it doesn’t make you happy, it’s plaque in the arteries of your life – and those of the world at large. It’s not the stuff we love and need that’s choking the world: It’s the novelty rubbish, the unused space, the waste. It’s the stand-by power or the light left on in an empty room. It’s the stuff we wouldn’t miss if it wasn’t there.

Good design – really good, brain busting, life-improving, back-to-basics design, is about knowing what you need and what makes you happy, and removing everything else. It’s no accident that Thoreau’s manifesto for the essential life is at heart a story about designing and building a simple house at Walden Pond. Inflating your house for the sake of fashion, or your designer’s own self aggrandisement, or because they just didn’t bother asking what’s important to you – that’s housing obesity.

Mies van der Rohe once famously said “Less is More”. Robert Venturi responded archly with “Less is a Bore”. For the sake of a trim, taught and terrific world, I’m going to propose some less incendiary and more realistic domestic dietary advice:

Enough is Enough”.

The top 10 rules for energy efficient house design – 05

January 21st, 2009

Rule 5: Mass is Critical

Corridor of Wistow Smart Farmhouse

If you’re interested in energy efficient house design, you’ve probably come across the very impressive sounding terms “thermal capacitance” or “thermal mass”.

The principle of thermal capacitance is pretty easy to understand: Heavy (or, more accurately, massive) stuff takes a long time to heat up. Once it’s hot it takes a long time to cool down again.

You’ve probably noticed this if you’ve ever stood against a west-facing brick wall on a cool evening after a hot day and felt the day’s heat still radiating off, or if you’ve felt last night’s coolness of concrete under bare feet on a summer morning.

Thermal mass, coupled with smart glazing and well-designed insulation, is one of the most important efficient-design tools available to an architect or building designer. It is most useful where temperatures swing between hot and cold, or in cold areas where heat sources, like the sun, are occasionally available. (It is less useful in hot, humid climates, where average temperatures are high, and cooling breezes must be maximised.)

Massive materials can store heat for a long time, and if designed properly, release it when it is most useful. Depending on the soil type, depth and structure, some well designed underground houses can access heat or ‘coolth’ from last winter or summer, 6 months or more ago. A concrete slab or thick masonry wall (300-400mm brick, stone or concrete) can release heat or ‘coolth’ from almost 6 hours ago.

Thermal mass can also be useful to draw heat from a space when too much heat is available, and re-radiate it later when temperatures drop. Some house designs can allow you to draw heat from one area (from the outside, for instance) and relocate it to another (to inside) – roof ponds or geothermal heating/cooling work on this principle.

There are situations where thermal capacitance is not useful. In spaces which must heat up or cool down quickly (for instance, when a heater is turned on in an irregularly used room), thermal mass will slow the heat response; a well-insulated lightweight room may be more useful.  And thermal mass can be awful when inappropriately used, as anyone who has baked in an uninsulated hot-box brick apartment on a stifling summer night (well after the outdoors has cooled) will know.

To use thermal capacitance advantageously there are a few questions you should ask:

  • Is thermal capacitance going to be useful to me? This leads to some other questions: What are my maximum and minimum temperatures? What is the average between these extremes? How long is the cycle between hot and cold?

  • How can I admit the useful and exclude the troublesome? (This might include shielding from extreme western sun, designing windows and eaves to admit more sun in winter than in summer, or insulating the thermal mass from unwanted temperature extremes).

  • How much thermal mass do I need? There are rules of thumb for ratios of glazing-to-mass. For underground houses some site testing may be required.

  • How do I plan to use the space? Will the usage be regular or irregular? When is heat or cold more useful?

The thermal mass in the earth-coupled polished concrete slab and the internal paddock-stone walls in our Wistow Smart Farmhouse (pictured above) allow the living spaces inside to remain comfortable year-round. The farmhouse needs no mechanical cooling and a minimum of heating in winter, despite baking summers and cold, grey winters.  Note the overhead ‘clerestory’ windows - these can be opened during cool summer evenings to purge the heat absorbed by the stone walls and concrete slab during the day.


The top 10 rules for energy efficient house design – 04

December 16th, 2008

Rule 4: Don’t heat with one hand and cool with another

patio heater in snow

A large part of creating an energy efficient house is knowing how, when and where to keep the outside conditions on the outside.

And that’s not chicken-feed stuff: In Australia we spend about 44.7% of our residential energy usage – about 170 PetaJoules per year (170,000,000,000,000kJ, or about 5.9 million tonnes of coal equivalent )- on heating and cooling our homes. (That figure’s about 5.1 quadrillion Btu in the USA, equivalent to about 5401PJ or 186 million tonnes of coal).

That’s a mighty load of go-juice spent making the inside of our houses more comfy than the outside. And, depressingly, an awful lot of this energy goes to waste.

From my experience, there are three main ways our homes waste this heating-and-cooling energy:

The first path to waste in our homes – and by far the biggest, in the temperate-climate Australian context – comes from building houses that leak heat, inwards or outwards. There are two ways to fix this: To seal the gaps in our houses, where warm air can enter or escape, and to insulate, insulate, insulate.

The second is by failing to use what we get for free. Failing to admit winter sunlight, or failing to store daytime heat for night-time use (through thermal mass or other energy-storage systems). Failing to cool our houses through night-time breezes or convective cooling. Failing to use evaporation, or to plant trees in the right places.

The third – and in some ways the most insidious- is by heating with one hand and cooling with another.

You can see an example of this every time an air conditioner runs with uninterrupted summer sunlight beaming into a room, or trying to cool when inefficient heat-emitting appliances are running. (In our office our laser printer alone puts out enough heat to raise the temperature two or three degrees. Nice in winter, but not so much fun in summer).

I’ve heard it said that a problem well defined begins to solve itself, and that principle can be applied to energy efficient house design. Look at your site, your situation and your energy sources. Know where your heat is going to come from, your sunpath and wind directions, and you’ll begin to know how to shield from it. Likewise, knowing your potential paths of heat loss; your gaps and uninsulated areas, will show you how to block and insulate them.

The trick is to address your energy gains or losses at the source, rather than developing active systems to counter them.

It’s simple stuff, but even professionals get it wrong sometimes.  It involves a change of mindset – a new thrift, rather than just throwing more energy at a problem.

I once worked on a multi-purpose hall for a primary school where a mechanical engineer proposed an air conditioning system that over-cools the air, then precisely adjusts the temperature by re-heating it again. As he explained the drawings, I sat, dumbfounded. Worse, he was astonished at my astonishment.

This type of inefficient thinking is everywhere, and it’s madness.


National Greenhouse Gas Inventory, 1990, 1995 & 1999 Australian Government Department of Climate Change

2005 Residential Energy Consumption Survey, US Energy Information Administration

The top 10 rules for energy efficient house design – 03

December 9th, 2008

Rule 3: Insulate, Insulate, Insulate

 Wall insulation

Houses are, on the whole, fantastic things. They give us all sorts of benefits: Privacy, space to store our stuff and a whole life-support system of services and systems, from hot water to waste disposal..

But one of the main reason we decide to live in houses, rather than bedding down in a swag under a coolibah tree, is the controlled microclimate our houses allow us to achieve.

Face it: It’s hot out there. Or cold. Or windy, snowy, rainy or whatever.

So it makes sense to try to keep the weather we want on the inside, and the weather we don’t want on the outside. But there’s one big problem: our homes leak heat, both inwards and outwards, meaning the inside climate we’ve worked so hard to create is always escaping, and the less-than-ideal outside climate is eternally working its way in. What’s the biggest way to reduce that leaking? Three words: Insulate, insulate, insulate.

Most building codes worldwide now have minimum standards for insulation, and more and more people are retrofitting their existing homes with one sort of insulation or other. We all know that it’s good, and that we should get ourselves some. We have a rough idea that it works something like a blanket, slowing the transfer of heat from a hotter medium to cooler. We know that it helps to keep the outside out, and the inside in.

It should be simple – but it’s not.

A quick trawl of your search engine of choice for information about insulation will reveal a bewildering cornucopia of different types, materials, performances, measurement systems and purposes. The range of products can be bewildering, while differences in measuring insulation can be downright misleading.

Some insulation companies companies measure the thermal resistance of their products by ‘U’ value, most by ‘R’ value.  Each measurement means the opposite (A low U-value means a high R-value, and vice versa). To make things even more confusing, R-values are measured differently in metric (kelvin square metres per watt) and imperial (Degrees Farenheit square feet per Btu). (Note: 1K-m2/w = 5.67446 °F-h/Btu). Check carefully when you compare claims for R-values from overseas.

Some insulation companies measure the performance of their product by itself, and some publicise the ‘whole of wall’ or ‘whole of roof’ performance. Check the small print on any manufacturer’s literature for this. And it’s difficult to compare the performance of reflective insulation with bulk, as they work in entirely different ways.

So what do you need to know when insulating your low-energy house?

The first question you need to ask is “How much do I need?”. Statutory R-levels of insulation are usually set by your local Building Code (The BCA in Australia), but you do have to remember that these are minimum levels only. While a higher R-value is normally better, there are exceptions and there are points of diminishing returns. Getting an energy rating performed on your house design by an accredited house energy rater is often a good place to start. Some insulation companies also publish insulation guides for different locations; these can provide worthwhile advice.

The second question you need to ask is “What type of insulation is best for me?”. There are three main types of insulation available. Bulk insulation uses tiny pockets of air, which resist heat flow, and include Glasswool, Polyester, polystyrene boards and the various types of fluffy batts, blankets and blow-ins. Reflective insulation is great for reducing radiant heat transfer, and includes the foils and other shiny things. Composite insulation uses a combination of reflective and bulk insulation, and includes foil-faced boards, blankets and bubblewraps.

To choose the right type of insulation, you need to know what kind of heat it will be resisting; conductive, convective or radiant. Will most heat be moving outwards or inwards? You also need to know where it will be located and what the limitations of that location will be (how will it be installed? What conditions will it be under? Does it need to be fire resistant? Will it get wet? Will it need an air-space? Will it be crushed or moved by other building elements?).

The third question you need to ask is “How will it be installed?”. This is a biggie. As in every aspect of house design, detail is everything. A good insulation system will be worthless -or even dangerous- if badly or inappropriately installed. Ask your insulation supplier for their standard details or installation instructions, and don’t be afraid to change systems if the installation system doesn’t suit your house. Push your Architect/Designer to detail the installation well, and push your installers to do the job properly.

Insulation is, in many ways, the starting point for most low-energy house design. Get this wrong and everything else you achieve will be leaking out your roof and walls from day one.

The top 10 rules for energy efficient house design – 02

December 1st, 2008

Rule 2: Stop fighting the universe.

The milky way

The universe wants you to design an energy-efficient house. No, seriously; it does. Why else would so many things, from the tilting of the earth to the laws of thermodynamics, give you the tools to heat or cool your house for free?

More energy lands on the roof of your house than you’ll ever need to heat it. Last summer’s heat lies stored only a few metres under your feet, and last winter’s ‘coolth‘ only a short distance below that. Hot air rises, where it can be recirculated as required or vented to the sky at night. The evaporation of water draws latent heat, cooling the air. Glass transmits light (short wave radiation) but traps heat (long wave radiation). Light-coloured surfaces reflect. Mass provides thermal capacitance, carrying the day’s heat into a colder evening. Heat travels from warm to cold, but at different speeds through different media.

These basic physical laws give us passive solar heating, earth-coupled heat storage, night-time heat purging, subsidence (cool) towers, sunrooms, reflective foil and bulk insulation and the many other tools we can use for energy efficient house design.

The same tilting of the Earth on its axis which gives us winter also sets the sun lower in the sky, allowing heat and light to pass under deep eaves and further into a north-facing room (south-facing in the northern hemisphere). The increased azimuth of the sun in summer allows it to be screened, provided you calculate your sun angles and eave dimensions carefully. (Pritzker-winner Glenn Murcutt calls this “Letting the planet do all the moving”.)

These are not new discoveries. Xenophon of Thebes wrote about passive solar design in his Memorabilia (3.8.8-10) in 371AD, but the 20th Century experience of cheap ,easily accessible fossil fuel has allowed us to heat and cool our buildings through the application of brute force.

Now, brute force is a fantastic thing if you’re planning to wrestle a gorilla or launch a payload into orbit, but using it to warm or cool your house is just pure bloody-mindedness if there are cheaper and easier options available.

So before you turn the first sod or draw the first line for your new, energy efficient house, we recommend you ask yourself (or your architect/designer) the following questions:

  • Are we best using the house’s environment, climate and conditions?

  • Is there a path of lesser resistance to achieve the same levels of comfort and delight?

And my personal favourite:

  • What is the universe trying to give me for free?

By all means, create an energy efficient house because you’re concerned about energy independence, peak oil or climate change. But personally, I like energy efficient design because any other choice is just beating your head against the laws of the universe. 

Our attractive header picture is from Flickr creative commons, posted by Sir Mervs

The top 10 rules for energy efficient house design – 01

November 27th, 2008

Rule 1: Pick the Low Hanging Fruit

 Wistow Smart Farmhouse, design by Diagram Architects Pty Ltd

Its easy to get excited about the bleeding-edge gadget-end of eco-house design. Solar photovoltaics, thermal phase change materials, home automation, in-house fuel cells and other enviro-toys help us to shout our green credentials from the rooftops and still play with the coolest technology.wistow solar cells

And that’s OK if you’ve got the dollars to spend on it.

But it’s not where the real action is in energy efficient design. In fact, concentrating on this stuff while ignoring the fundamentals – the flow of heat, light and electricity through the everyday materials of your home – is throwing money away for minimal ecological benefit.

The trick is to start with the easy, effective changes; the things that will give you the maximum impact for the minimum cost, risk and commitment. In fact, some of the most effective changes involve the smallest investment, and start paying you back almost immediately. This is what we mean by “Picking the low-hanging fruit”.

The benefits of this approach are obvious and immediate. Here’s an example:

Some time ago, we were approached by a homeowner who was looking at installing a roof-mounted solar panel system to fully offset his home electricity usage. His electricity bills were substantial, and a solar system with the capacity to offset them entirely was well out of his budget

A quick review of his home revealed (amongst other issues) 110 50w halogen downlights cluttering his ceiling. Assuming a conservative average of 3 hours on every night, that’s about $940 on his annual electricity bill for halogen downlights alone.

Just replacing his 50w globes with 35w IRC halogens (same light output and quality) at a total cost of about $900 would save about 1806 kilowatt-hours per year – that’s an annual saving of about $280. (He’d save even more replacing them with compact fluorescents.)

Compare that with that a 1.5kw grid-connected solar system costing about $12,000 (including the federal government rebate) which only generates about $233 worth of power over the course of a year (that’s a payback period of 60 years).*

That’s right – an investment of $900 on everyday-tech light fittings saved more electricity and greenhouse pollution that $12,000 of solar technology.

If this homeowner had spent his $12,000 on solar power, without upgrading the efficiency of these and other basic items, every single watt of power generated from the sun would have been used to power a ceiling packed with unnecessarily (and expensively) greedy downlights.  Instead, we recommended that he spend less than 10% of the cost to make up the difference through simple, off-the-shelf efficiency measures.

I don’t want to knock solar photovoltaics. We’ve designed several buildings fitted with them, like the Wistow Smart Farmhouse in the picture above. But if you don’t sort the simple things first, you’re paying serious money to waste the energy you generate with them.

So what are the simple things? Watch this space.

*Costing information