SCP and bere:architects came up with the concept of a 'Zero-Zero' building (net zero in embodied carbon and net zero in operational carbon emissions). Put simply, this is achieved by minimising the embodied carbon emissions of a building during its construction phase, and making it plus-energy during its performance phase, so that over 60 years the embodied carbon emissions are paid off, in net terms, by the excess energy produced by the roof-mounted PV array, even after taking into account all of the 60 years in-use occupant energy requirements and all the carbon emissions from 60 years of maintenance.
SCP found that the tiny in-use 'operational carbon emissions' of the Passive House amounted to 83% of the total carbon emissions over 60 years, while the 'construction stage' embodied emissions amounted to just 7% of the total energy used over 60 years. 'Product stage' embodied emissions were found to be just 6% and 'end of life stage' emissions just 4% of the total carbon emissions.
In conclusion, the operational energy requirements of the Chestnut House Passive House were found to be so small that the roof-mounted PV array produces more energy in a year than all the operational energy requirements of the building and its users. Because the Passive House building produces a surplus of energy and the embodied energy of this house is so insignificantly small, the surplus energy produced by the PV array will 'pay back' all the embodied carbon of the house within 60 years in net terms, even taking into account the carbon-cost of 60 years of annual and periodic maintenance cycles.
For the whole of its life, the Chestnut House will act as a power-station for the grid. The first 60 years of surplus energy can be seen as paying off its embodied carbon debt. The next 60 years of life will produce the zero-carbon energy needed to produce its eventual replacement building, and beyond that it's surplus energy can be seen as a zero-carbon energy contribution to the other needs of society.