An average 85m2 UK home of brick and concrete is said to release 68 tonnes CO2 in construction. For a building like ours of 643m2, we would expect to release something like 450 tonnes with conventional construction.
Using Alternative Construction the picture is more like this (from the ground up):
Crushed Concrete MOT Type-1: Waste product, minimal embodied energy of crushing and delivery. Plant is under 10 miles from site.
Scrap Tyres. Waste product past end of life – virtually no embodied energy. Since they are now repurposed, they are also saved from landfill.
Pea Shingle – (packed into tyres) refined and washed in Kent, 2 hour’s drive of site.
Concrete deemed necessary : less than 0.5 tonnes embodied CO2.
Timber Frame, sustainably forested, including windows and ground floor: Approximately 85 tonnes SEQUESETRED CO2 – more than offsetting milling and transport costs.
Straw Walls: waste product, past end of life. 3-hour drive to London. Approximately 35 tonnes SEQUESTERED CO2
Lime: gives off CO2 in manufacture (like cement) but, unlike cement, reabsorbs it as it cures, forming Calcium Carbonate. Generally considered carbon neutral apart from transportation – 3 hrs drive
Clay: carbon neutral. Dug and processed on site. Secondary layers processed in Germany – embodied energy: mainly transportation.
Windows: triple glazed, manufactured in UK and Poland. 7 tonnes embodied C02, (compare 8.2 tonnes PVC-u) Carbon savings in use will recoup the embodied energy within 20 years.
Roof Covering: 99% Recycled waste product – IkoSlates. Total embodied energy has been independently calculated at less than any alternative.
Solar panels: embodied energy recouped in less than 2 years – thereafter carbon negative.
Energy: all electric supplied mainly by solar PV and ASHP.
Air-Tightness will achieve a score of 2.5 or lower.
Energy Profile in Construction: minimal use of plant such as excavators; zero use of cranes. Majority of construction processes manual.
Energy Profile In Use – minimal due to excellent thermal insulation.
Lifespan: up to 200 years
CONCLUSION: The sequestered (ie captured) CO2 in timber and straw) more than offset the embodied carbon in other materials, bringing the whole construction process to a Carbon Negative figure of around 90 tonnes. This compares to a Carbon Positive Footprint of around 400 tonnes had we used conventional construction materials and processes.
Thanks to minimal energy emissions in use, our building is still likely to be Carbon Negative at the end of its useful life. Compare this to the hall built with conventional means 450 tonnes / 200 years – a minimum of 2.25 tonnes per year, plus C02 released in use.
Add to this 331 tonnes CO2 avoided through use of Solar PV over 60 years, plus 28 tonnes through avoidance of concrete. the total negative carbon footprint of our building is -479 tonnes.