The Insulation Sweet Spot

How much insulation is enough?  If I double the R value, does that mean I halve my heating and cooling loads?  Unfortunately it’s just not that simple, increased insulation has diminishing returns in reduced heat transfer.  To explain this, first, let’s start with carefully defining R Value.  It’s a measure of resistance to heat transfer and can be stated as follows:

Using the above formula gives the R value in SI units which we will work in for the rest of this article.  To convert to US Imperial units, you need to times the RSI by 5.678.  Now lets use the above formula and apply it to an example of a wall. We want to calculate the heat transfer value, which will then give us the heating/cooling energy requirement for our heating/air-conditioning system and from that we’ll be able to work out the cost. The formula now looks like this:

The assumptions we are using are below, some of these are inflated to accentuate the potential savings:

  • Area of external wall: 100m2
  • Temperature difference between internal thermostat set point and external temperature: 15 Degrees C (quite a difference, either hot climate trying to cool or cool to cold climate trying to heat)
  • Coefficient of Performance (COP) of Heating or Cooling Device: 2.5 (relatively poor)
  • Assume that we are paying $0.25c for every kWh of delivered energy to the building
  • 24 hour average occupancy, so continual maintenance of desired temperature.

We’ll start with a single brick wall (RSI Value of 0.106) and then slowly increase the insulation to determine how much money we can save. Here’s how much the heat transfer reduces as R value increases:

As you can see, the reduction in heat transfer is huge, at least initially. In fact nearly 80% of the heat transfer is stopped with just RSI0.5 insulation. As you increase the R Value further the savings in heat transfer drop off significantly:

  • RSI0.5 to RSI1.0: 11% extra heat saving
  • RSI1.0 to RSI2.0: 6% extra heat saving
  • RSI2.0 to RSI3.0: 2% extra heat saving
  • RSI3.0 to RSI4.0: 1% Extra heat saving

So what about the effect to costs? See the following graph for the details on the heating and cooling cost savings for our conceptual building:

Once again, we see a very big drop off in savings as R Value increases. And these savings are potentially inflated, if the average internal temperature to external temperature difference was halved to 7.5 degrees C, we’d see these values halve also.
There is obviously a sweet spot somewhere between RSI1 and RSI4, probably around the RSI2.5 mark. Of course, this depends on the insulation costs, the cost of the structure to house the insulation and the design life of the building. For example, going from RSI2 to RSI4.0 may only require a small increase in insulation costs, but if the wall framing need to be increased in width by an inch, this could be quite costly.

The other important consideration here is that this is all based on theory. What is actually going to happen in an average building is probably going to further lessen the impact that your wall insulation has on your heating and cooling costs. For example, if you poked five small 100 x 50mm holes in the insulation of our conceptual house, depending on drafts etc, you’d probably reduce RSI3.5 walls insulated walls to the equivalent of RSI3.0.
In windy climates or pressurised buildings, this could be a lot worse. Similarly there are likely a lot of other easy wins to increase the actual performance of your house that don’t relate to your wall insulation, for example:

  • Glazing type (R Value)
  • Glazing area (lots of windows usually means lots of heat transfer)
  • Floor insulation (appropriate in cooler climates)
  • Floor ground coupling (appropriate in warmer climates)
  • Efficiency of your air-conditioning and heating system
  • Cost and carbon intensity of your energy supply source (eg gas verse electricity)

I hope this helps explain the R Value sweet spot.
For the control freaks out there who want to know exactly where that is for their particular building/climate/energy mix etc, get in touch!

What’s Carbon Got to Do With Me?

This climate science is pretty complex right? I mean, they say a butterfly flapping its wings can cause a chain of events that leads to a cyclone on the other side of the world. How then can we even begin to understand what the burning of fossil fuels is going to do to our climate? The answer isn’t entirely simple, it’s often made out to be a lot more complicated that it needs to be. Here’s how I see it.

CO2 Leads Heats The Surrounding Atmosphere More than Normal Air Does

There’s some complex physics behind this one, so let’s forget about the physics and just watch this experiment which displays it perfectly:

Absolutely a simplification of what’s happening on planet Earth, however, it does demonstrate a fact that even the most sceptical of people have to agree on, ALL ELSE BEING EQUAL, CO2 causes more heat gain in the atmosphere than normal air. There are many more similar videos of experiments on the internet simulating the same cause and effect. Myth busters even have one here. But how does this fact pan out in real life, how do we model what will actually happen to the atmosphere, or more importantly the entire planet, if we keep up our current rate of carbon pollution?

Predicting the Outcomes of our Greenhouse Gas Pollution

So how do we respond to this information? To do so in an informative manner we need to determine what the likely effect of greenhouse gas pollution will be. If the effect is negligible there’s nothing to worry about. The waters really get muddied here though because although we can calculate the warming effect of CO2 if all else is equal, all else isn’t equal. In fact, it’s very complex.
Nature responds to different concentrations of CO2 in the atmosphere in a variety of ways. Some of these responses reduce temperature (mitigating effects), some increase it further (amplifying effects). For example, the ocean uptakes CO2 as the levels increase in the atmosphere (it effectively becomes a little bit more acidic), a mitigating effect. However, conversely, as the oceans warm there is a risk that buried deposits of frozen clathrates will melt and cause large releases of methane (another greenhouse gas) into the atmosphere. There are probably thousands of these mitigating and amplifying effects and many of them we haven’t even thought of, can’t quantify or can’t predict when they will take effect.

This leads us to rely on empirical modelling. Basically, take a look at history and determine what the world was like with different levels of CO2. We can do this with modern day records and also pre-historically with ice cores and fossil records. They paint a pretty obvious picture, and that there is a very strong relationship between atmospheric CO2 levels and average surface temperatures around the globe. Check out the latest research on this here conducted by Berkeley University. This is a very interesting study, it is my understanding it was set up because of some perceived discrepancies in the accuracy of similar studies conducted earlier and it was thought by many that the results would likely discredit the former studies. Well, the results are out and they support the former studies entirely. Indeed the head of the study, physicist Richard Miller had this to say:

“Three years ago, I identified problems in previous climate studies that, in my mind, threw doubt on the very existence of global warming,” the physicist wrote in an op-ed piece published in the New York Times.

“Last year, following an intensive research effort involving a dozen scientists, I concluded that global warming was real and that the prior estimates of the rate of warming were correct. I’m now going a step further: Humans are almost entirely the cause.” (See article here)

Why is he now worried, this graph probably explains it quite well:

What the above graph shows is that we can very accurately predict temperature rises with CO2 increases in the atmosphere. So although we can’t be exactly sure of all the mechanisms (mitigating and amplifying) that are leading to a warmer climate due to CO2 increases, the evidence is extremely compelling that CO2 increases result in increased temperature.  

More historical records support this theory. By measuring captured air from ice cores drilled from huge glaciers dating back thousands of years and matching this to fossil records to determine sea levels we also know that higher CO2 levels in the atmosphere corresponded to times of higher sea levels (warmer atmosphere, less ice at the poles). Once again, although we don’t know all the exact mechanisms that cause the warming, the evidence is compelling that CO2 increases result in increased temperature.

Our Part in Climate Change

Now think back to that last blog post I wrote on Australia’s energy use. Taking this information, in conjunction with the evidence above, we need to take personal responsibility for climate change. It is my responsibility, as well as yours, that we are changing the climate due to our huge thirst for cheap energy and consumer goods (which rely on cheap energy to manufacture). There is no point sitting back in a comfy arm chair pointing the finger at the coal fired power station and proclaiming “they are polluting our atmosphere!”. It just so happens that the factory that made the comfy arm chair needed the power from the power station (and your TV which is receiving the images of the terrible polluting coal fired power station, was also made with the help of coal, and relies on coal to work). We all need to start drawing these connections to truly understand our responsibility.

Once the connection is made, next step is determining our response.  But in order to do that we really need to know what a warmer planet means, for example, if a warmer planet is better, then why worry? I’ll explain that in some details in my next blog post on this topic.

Check out the sources of the article here:

Global Warming in a Bottle:

Myth Busters:

Oceam acidification (mitigating effect):

Clethates release (amplifying effect):

Prehistoric Climate and CO2 Relationships (example study):

Green Swing Rainbow

The Green Swing Project Update

The Green Swing project is an innovative, sustainable development of four dwellings in Perth’s inner city.

Building their very own dream sustainable homes are couples Mark and Alana Dowley and Helmut and Eugenie Stockman. They want to demonstrate that you can create small scale inner city living environments in Perth which:

  • Are the most sustainable
  • Promote community feel and encourage creativity
  • Are of high quality
  • Become a showcase for future increased density sustainable development
  • Generate interest and inspire real change.

The project in short

  • 96 Rutland Avenue, Lathlain
  • Block size 837sqm
  • Zoning R40/60
  • About 5km from CBD
  • 400m from train station
  • Close to shops & facilities
  • 2 townhouses, 2 apartments
  • Purchase land January 2010
  • Planning approval December 2010
  • Building approval October 2011

After two years of intensive planning, building work started in December 2011.

The project consists of two townhouses and two units which have been designed using three construction types: reverse brick veneer, strawbale with earthen render and double brick.

Design features include:

  • Solar passive design
  • Grey and rainwater harvesting
  • Solar PV system
  • Solar hot water system
  • Green concrete
  • Double glazed windows with wooden frames
  • Insulation using recyled wool and Greenstuf (plastic)
  • Recycled materials: straw, bricks, timber, interior wood, wool, plastic bottles.

Although straw bale construction is considered an usual material choice, it is becoming more popular due to its excellent insulation properties. It is also a waste product that can be sourced locally product, offers the thermal mass needed and is biodegradable and recyclable.

Helmut and Eugenie chose to build with straw bale and are making great progress. The perfectly straight two story walls went up at the start of August and the render was put on just last week.

Last November, eTool helped the couples calculate the total impact of the entire development. Due to them building a medium density development, in a low density area, their design life is 115 years which is very high for inner city architecture. Overall, they achieved a Gold rating and saved a huge 108% of carbon against the benchmark. The full case study can be found here.

The Green Swing have also arranged a lease arrangement between the local council and local community garden association which allows for the re-vegetation of the “Sump” drain site next door at 98 Rutland Avenue to create a community garden and for everyone to enjoy. With the help of Josh Byrne, they have come up with this landscaping concept including native vegetation and a food forest.

Construction is on track to be finished by the end of the year/start of next year and The Green Swing couples and kids can’t wait to start enjoying all of their hard work in their very own dream, sustainable homes!

To follow the progress of The Green Swing project, find them on Facebook or visit their website.

Built Environment Adaption Framework


The Australian Sustainable Built Environment Council (ASBEC) proposes an Adaptation Policy Framework to improve the resilience of the built environment in the face of climate change.

This framework aims to:

  • Protect the wellbeing of communities through targeted policy initiatives and better urban and building design;
  • Ensure appropriate institutional arrangements to facilitate adaptation;
  • Realise economic benefits from early adaptation through effective strategic planning and risk minimisation;
  • Advance sustainability through better resource and risk management strategies; and
  • Increase community education and awareness about climate change risks and adaptation.

10 key ideas have been forward to demonstrate who the government can reach these goals.












Read the entire framework here.

Read the accompanying report here.

The Sustainable Streets & Communities Plan

Henrique and I recently went down to Freo to attend a talk by Michael Mobbs of Sustainable House fame. Michael is a sustainability consultant who decided to build himself and his family an entirely self sufficient home in Sydney about 15 years ago.

As well as talking about how to build sustainable homes, Michael shared his passion for creating communities that could grow their own food, recycle grey water and take back the power to make where they live and work greener and more sustainable.

Chippendale – where Michael lives – has become a shining example of how successful such a plan could be. Critical to the plan is community involvement and volunteers; with people offering their time to weed, mulch, make new garden beds, aerate the compost and plant seedlings etc. Food is grown on roadsides, around trees, on rooftops or basically anywhere there is potential to grow herbs and salads to seasonal fruit and vegetables.

In 2010, Michael was commissioned by the City of Sydney to come up with a sustainable community plan based on Chippendale that they could role out to other cities.

After initial resistance to The Plan and a national petitioning campaign, the City of Sydney Environment and Heritage Committee has this week recommended a public exhibition of the Sustainable Streets and Communities Plan for public comment.

At the heart of the plan are ideas to lower our consumption and waste, reduce our GreenHouse Gas emissions and slow down climate change. Projects include ways to utilise rainwater, reuse grey water, lower the temperature of roads and create more space for community use.

Michael believes that through the plan, it will only take 10 years for the suburb to get all of its water from rainwater. reuse all sewage and have more than 30 per cent of food grown in urban farms, road gardens and rooftops.

To get involved or learn more about becoming more sustainable in your community, join the conversation on Facebook or Twitter.