Measuring the full carbon footprint of homes

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Carbon emissions from Homes – Is the BER just half the story?

The BER (Building Energy Rating) gives a standardised figure for the carbon emissions from heat, providing hot water and electricity to light and operate our homes. We highlighted in a previous blog, that it does not cover the electrical equipment we plug in. Homes are becoming ever more efficient with new regulations such as the near Zero Energy Building requirements (nZEB) which are being implemented through the building regulations in 2019.

But before they are even occupied, new homes have a huge impact on the environment. Materials have to be quarried, mined or harvested, transported to factories and manufactured. The final products have to be transported to the building site, lifted into place and fixed in position. All of this leads to one huge ‘carbon burb’ in the relatively brief period before the home is occupied. Given the imminent peril the planet is now in, can we afford massive spikes in carbon emissions even if it results in very efficient homes?

As regulations make new homes ever more efficient the proportion of these construction related carbon emissions are rising as a proportion of the overall life cycle of the home, and could be the equivalent of 25 to 50 years of operation as measured by the BER. In one UK study it was shown that the construction carbon emissions for an apartment block  was equivalent to the entire heating, hot water and lighting for 50 to 60 years.

As with energy efficiency the maxim ‘measure and reduce’ applies. That is why we have been able to improve the energy efficiency of new homes by over 60% compared with ten years ago. Unless the home builder and his architect are aware of what the construction carbon footprint is, it is unlikely that they will know how to reduce it.

Certain design concepts may require more materials than others. Obviously larger homes require more materials and therefore require more carbon emissions and resource use, but simple things like the shape and type of home will also have an impact. If walls, floors and foundations are shared with other dwellings then the impact should be lower per dwelling. For single dwellings more compact shapes save materials, as a square encloses more space with less wall area and foundations than an elongated rectangle.

In order to do a carbon footprint calculation, the builder’s designer need to be able to work out the quantity of each product  used and the environmental footprint (or impact) of each product. It helps if every product manufacturer has already provided a 3rd party verified carbon footprint through Environmental Product Declarations (EPD). Otherwise the designer needs to find data for a similar product but this will be less accurate. Luckily it is becoming more common in Ireland as programmes like Home Performance Index ask for EPD, and many of the main construction product manufacturers either already have them, or are starting to develop them. You can see which producers already have EPDs on the EPD Ireland website.

Certain types of products will have higher carbon footprint than others. Typically for standard cement, one ton of cement is emitted for every ton produced. Indeed it is estimated that the production of cement is responsible for 6% of global carbon emissions. Wood based products generally have a lower carbon footprint. There is little point in having a very low carbon product if it needs to be replaced several times during the lifetime of the home, so this also needs to be considered.

Whilst calculation of the full environmental footprint of homes is not yet common in Ireland this is likely to change in the next couple of years as Home Performance Index asks for it and as more attention is focused on it. Most building professionals are, (or at least should be) aware of how to achieve a low energy/carbon house in operation. The next step is achieving low carbon homes across their full life cycle from construction, through operation, maintenance and finally to deconstruction at the end of life.

For more information on EPD Ireland:

The ten commandments of reducing carbon:

Download the Irish Green Building Council’s -Towards the Circular Economy Report: