Summary

This page expands on the topics raised in the ‘Carbon Emission Driven Climate Change‘ section of the Sustainability page.  It provides the calculations that show that the buildings on the ideal, conceptual, site would be Carbon negative during use.

In the UK, on average, a typical new home emits between 1 and 2 tonnes a year through operation (being lived in) and an average of 50-80 tonnes is emitted through building each dwelling.   The high emissions from the current standard of modern homes are
compounded by the fact that the building are short lived (the average new build will require a major reconstruction every 80 years).  
Which when annualised comes to 0.6 to 1 tonnes per dwelling per year.  This gives an overall positive carbon foot print of 1.6 to 3 tonnes CO2e per year per dwelling .   All contributing to climate change – contrary to the UK’s Climate Change Act commitments (and the NPPF’s commitments to this act).

The Deeping Project dwellings would be approximately 2.6 tonnes a year carbon negative per property through operation and the carbon emitted during construction when anualised over the likely lifespan of the property will be in the order of 0.2 to 0.3 tonnes a year.  This gives an overall negative carbon footprint of – 2.3 to – 2.4 tonnes of CO2e per year per dwelling.  Helping to reduce climate change.

Carbon Emission

The buildings featured in this blueprint are all based on the design used in the planning application 17/01644/FULLS. These homes had a design SAP rating of 130 (a 30% improvement on ‘zero carbon’).  Once operational, the four bedroom versions would be 2.6 tonnes a year carbon negative so not only offsetting the carbon footprint of the community, but also helping to reduce the UK’s overall carbon emissions total.

The embodied carbon generated during the building of these homes would be minimised by the use of recycled materials and wood. It should be possible to make up a large proportion of the thermal mass within these dwellings with recycled building materials. In addition wood, particularly oak, has a higher specific heat [1] than concrete and will also provide an efficient way of locking captured carbon into the building.  The science of reducing the embodied carbon element of home construction is in its infancy and this development would be used to help push the experimental boundaries.

Digital sensors would be installed into a selection of the buildings to provide detailed performance feedback on the first few years of habitation. This will provide data that will allow further improvements in future eco developments.

Carbon emission during habitation

This development would reduce the UKs total annual carbon emissions by approximately 156 tonnes (60 * 2.6 tonnes) of carbon a year.

As a comparison the equivalent number of traditional modern dwellings would add approximately 60-120 tonnes a year to the UK’s total annual carbon emissions.

This is calculated by using as examples the houses currently under development at Ganger farm near Romsey in the Test Valley. These all fall into the Energy Performance Certificate ‘B’ band (found from the national EPC Register using postcodes SO51 0DJ and SO51 7UD.). These EPCs show that their average annual carbon emissions are in the range of 1.5 to 2.5 tonnes of carbon per year.  The 275 houses being built at Ganger Farm (14/01090/FULLS) are therefore going to add in the range of an extra 400-500 tonnes of carbon to the annual UK emissions total.   This doesn’t include the carbon emissions generated actually building these homes, just their operational emissions once they have been built.

Extrapolating these figures to the total number of houses built annually in the UK (which was about 165,000 in both 2017 and 2018) then the annual increase to the UK’s Carbon emissions caused by just operating these new homes is an extra 0.25 to 0.41 million tonnes a year.

Embodied Carbon (carbon emitted during house building)

If we look again at the Ganger Farm development example, the floor areas of the homes being built are about 80-110 m² (figures from the EPC register). Using an average embodied carbon metric of 700 kg per m² this gives total building emissions of 56 to 77 tonnes of carbon per property or an initial build of 15,000 to 20,000 tonnes of carbon from this one development alone. If measured over an expected lifetime of 80 years (effectively the buildings will have to be reconstructed every 80 years) then this figure works out at about 0.7 to 1 tonnes of carbon a year per property.  So if the annualised embodied carbon figure (total carbon from build divided by expected life of the building) is then added to the operational carbon figures given above, the Ganger Farm development properties will each be adding 2.5 to 3.5 tonnes a year to the UK’s carbon emissions so in total Ganger Farm will probably be contributing in the order of 600-700 tonnes of carbon a year to the UK annual emissions total.

Again extrapolating these figures to the total number of houses built annually in the UK (about 165,000) then the gross embodied carbon emitted by building these homes is 9.2 to 12.7 million tonnes a year. This is a 2% to 2.5% annual addition to the UK’s current total annual Carbon emissions.  Even if this is annualised this is 115,500 to 158,812 tonnes of carbon a year.  It is important to remember these are significant net increases to the UK’s carbon emissions at a time when the UK is committed to reducing these figures.

Even if the construction of the earth sheltered homes emitted twice the carbon of the Ganger farm new builds, when annualised over the expected lifetime of many hundreds of years their footprint will be much smaller (and will also be offset by their being Carbon negative in operation).   The 112 to 154 tonnes a property (200% of the 56 to 77 equivalent Ganger Farm properties) when annualised over a possible 500 year lifespan (and there are plenty of functioning 1000 year old concrete structures) is 0.22 to 0.31 tonnes a year.

Nobody can now seriously claim to be unaware that carbon emission is damaging the climate and the environment we are living in. Carbon emission is definitely ‘compromising the ability of future generations to meet their own needs‘ (the NPPF definition of what isn’t sustainable). The conclusion has to be that the current methods of house building cannot be considered ‘Sustainable Development’ anymore and they are undermining the country’s commitments to the Climate Change Act.  Given the large proportion of the act’s target that domestic buildings contribute, this has to be an issue that needs to be addressed with urgency.

Footnotes

[1] Specific heat is a measure of how much thermal energy a material can hold.  Concrete ranges from approximately 840 J/kg·K to 1800 J/kg·K and oak is 2400 J/kg·K. This makes oak a third better than the best concrete but as it isn’t as dense twice as much oak would be required to get the same thermal capacity.