“What are we trying to achieve” was the question we set ourselves as we embarked on our self-build project. You cannot build what you want until you are clear about what you want.

We decided:

1. That we wanted to minimise our daily carbon footprint in the finished house by building an energy efficient house. A house that would be powered solely by electricity with zero emissions at the point of consumption and a house that could generate more electricity than it would consume each year.
2. We wanted a high level of environmental comfort in the house that included a stable internal temperature, low and stable humidity, a quiet environment and plentiful natural light.
3. We wanted to use sustainable and local materials where possible in constructing the building and wanted to avoid the use of chemicals that would emit toxic gasses.

We took these objectives to a local architect and discussed the various design and energy performance standards. We settled on the PassivHaus standard.

The PassivHaus standard requires that space heating / cooling energy demand does not exceed 15 kWh per square meter of treated floor area per annum. The average UK home is estimated to require around 140 kWh per square meter per annum.

Total energy consumption including all heating and cooling as well as cooking, hot water and all domestic energy consumption must not exceed 60 kWh per square meter of treated floor area per annum.

A PassivHaus is required to meet an air tightness standard of less than 0.6 air changes per hour at 50 pascals of pressure (N50) to ensure there are no uncontrolled draughts and air leaks but with ventilation, should achieve an air change rate of 0.37 air changes per hour (all air is changed every 3 hours, keeping the air fresh and removing any pollutants).

There are PassivHaus standards for thermal insulation, window performance, ventilation and heat recovery, absence of thermal bridges and thermal comfort.

With vital design decisions made and standards adopted some aspects of architectural design were inevitable. For example, large windows on the east and south sides of the building to maximise thermal gain from sunlight during the winter, overhangs and other shading strategies to keep the high summer sun off the windows. All water kept to one small area of the house to minimise pipe runs and heat loss from piped but unused hot water. Small bore hot water pipes with individual supply pipes to each tap from the tank to provide fast delivery of hot water with minimal heat loss. Minimal windows on the cold north side of the house to minimise cooling and small windows on the west to avoid summer overheating. Right angles where possible on the building exterior – because all other angles are less easy to insulate.

Once the architectural designs, thermal designs and energy designs were agreed, planning permission granted and detailed drawings prepared we were ready for ground works.