Three and a half years later - would we do this again?

Yes - three and a half years have passed, and the house has matured (and so have we!).
Were we to do this again, then quite a lot of things would be done differently. So some reflections ...

Too much emphasis in the design on appearance and it was left to us to research and implement all the environmental features - extremely efficient insulation, triple glazing, a passivehaus foundation and more, local labour, and as far as possible local sourced materials. It looks attractive but has more than 20 corners making it more expensive to build and much more difficult to make airtight.

The extra cost of including green energy and water technology was worthwhile - though today some of this would have been done differently. Taking advantage of government incentives to encourage the take up of renewable energy has been controversial and not well managed by government. Doubters said we would never recoup the money (£28,000 or so) spent to put 9.8kW of solar PV on the barn in 2011. In fact it paid for itself in 7 years and will almost certainly continue to produce an average of 9500 kW hrs of clean energy every year for at least another 25 years - probably more. More than 70,000 kW generated so far; less than 50,000 used with the rest exported to the grid. Now you could install the same 9.8kW for well under half the cost and in many cases would be cost effective without any subsidy. During the first year - a rather a cold one - the house needed what we regarded as an excessive amount of electricity from the grid.

The solar water heating provides virtually 'free' hot water for more than 6 months and valuable base-heating of the 800l thermal store for the rest of the year. Though widely regarded as one of the most efficient and effective solar installations - mainly in passive houses - it was failed by the nuclear expert the government sent in to inspect it and it took him well over an hour to find out how it worked. Why did it fail? Because some of the heat it generated from the sun was contributing to heating the house; it should only have been used to produce hot water. So the government grant withdrawn in favour of supporting less efficient installations.