The simplest approach to calculating your carbon footprint is to use one of the many calculators on the Internet. These offer a simple approach that uses average values for the area in which you live, and the type of building you occupy. You need some simple information such as your power and fuel bill.

We decided to develop our carbon footprint from scratch, so that we could get a better understanding of the process. This is how:

Energy is assessed by looking at your quarterly energy bills. The electricity in your town may come from coal, gas, hydro, or wind sources and each of these has a different carbon emission. We found the conversion factor to calculate the carbon emissions for Adelaide's grid-supplied power at the National Carbon Accounting System's web site.

The next step was to estimate how much electricity was used by each of our appliances - all the lighting, heating, cooling, hot water heating, fridge and cooking appliances. We ended up looking on the back of most things, to see how much energy they used. Then we multiplied that by the number of hours a week/year we used the appliance. These were estimations, but they came in fairly close to our energy use over the year. The first table below shows our lights, and the second table shows all the other appliances.

You can convert all your individual items from power use to carbon dioxide emissions if you like, or you can just work them out as percentages of the total power usage, and compare the percentages to the carbon emission total of your power bills.

Water that arrives at your house through the water mains has used energy. It has been filtered and cleaned and pumped down the pipe. SA Water told us that the carbon emissions from 1 kilolitre (1000 litres) of water is 1.72 kg CO2. You need to multiply that figure by the number of kilolitres of water you use each year. Your water bill tells you how much water you have used.

Wastes that leave your property also give rise to carbon emissions - they are taken to a tip in a truck, and then they rot, causing methane gas to form. Methane is a very strong greenhouse gas. You also have wastes that leave your house in pipes, to the local sewage works.

Calculations for municipal sewage treatment are based population, not on volume, and so we came up with a 'population' for the Meeting House based on 30 people for 8 hours a week, then dividing the result by the actual hours in a week. This provides a population of 1.42 people for our Meeting House, and by using the factors provided in the Australian Greenhouse Office Methods and Factors Workbook, we calculated that the total CO2 emissions for treating our sewage would be 201.6 kg per annum. The Australian Government regularly updates its technical notes on emission factors, so you should check out the latest version.

Rubbish production is calculated by adding up how many bins you have collected each week - are they always full, only half full, a bit of both? The Meeting House produces 35L of mixed household waste per week, or 1820L mixed household waste annually, with a greenhouse impact of approximately 450kg CO2 per annum. And yes, the factor is in that workbook from the Australian Greenhouse Office.

If green waste is sent to landfill, it would generate methane, a greenhouse gas that is 21 times more damaging than carbon dioxide. However, if this waste is sent to a composting facility as part of your Council’s kerbside green waste program, the emissions of carbon dioxide are reduced to zero. The carbon in composted leaves is sequestered as part of the ‘carbon sink’ in the soil. The Meeting House produces 6240L of dried leaves each autumn, which are sent to a composting works. If they went to landfill, they would generate 624kg CO2. Once again, you need to look up the Australian Greenhouse Office's workbook to see what the emissions are for your type of greenwaste.

Embodied carbon is the amount of carbon emitted in the production of the materials used to make your building. Some materials like concrete are made by burning limestone, releasing huge amounts of carbon dioxide, while other materials such as wood or natural stone are produced using smaller amounts of energy. For the purposes of an audit, it is assumed that a building lasts about 40 years, and so the embodied carbon is divided by 40 to obtain the annual figure. If your building is very old, as our Meeting House is, this will overestimate the annual embodied carbon footprint of the building.

Finding out what the embodied carbon content of your building is can be challenging, but the Edinburgh Centre for Carbon Management (ECCM) has a free calculator that can help you. We used information from ECCM, and in the case of our Meeting House the embodied carbon content for all the buildings on the site looked like this:

Embodied carbon is also found in the the furnishings and fittings inside the building. In most cases, a standard figure is used that estimates the 'normal' carbon footprint of the 'average' family. Finding actual factors for different types of furnishings, floor coverings, wall treatments, and appliances is not easy. These days, some companies put the carbon footprint emissions on their labels, so you may be able to compare new items that are similar to items you already have.

The table below shows some of the emission factors for typical 'maintenance' activities from inside jobs like replacing the carpet, to outside tasks such as recladding or reroofing:

So now, all you have to do is add it all up!

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