The practice has always been involved with sustainable construction – the first thing we built was a low-energy house at the Energy World exhibition in 1986, built to demonstrate simplified building methods which we used to run training courses for self-builders.

Phil Bixby trained as a Certified Passivhaus Designer in 2010, as soon as the training became available in England. The Passivhaus approach involves careful design to to incorporate:-

• High standards of insulation
• Minimising thermal bridging (weak points in the insulation at junctions etc)
• High standards of airtightness coupled with use of mechanical ventilation with heat recovery
• Careful positioning of glazing to make use of solar gains when wanted, but avoiding summer overheating
• High quality windows and external doors, with triple-glazing as standard in the UK

This care continues into construction with the contractor and architect working together to ensure the building gets built according to the drawings. Airtightness tests are carried out to ensure unwanted leakage is dealt with and the final building is draught-free. Certification is carried out by an independent certifier.

The end result is buildings which are comfortable, where the energy requirements for heating are very low and known accurately in advance. No conventional central heating system is needed.

The main tool for this work is the PHPP design software. Phil uses this on most projects – Passivhaus or not – simply to gain a clear understanding of energy needs and to avoid summer overheating, which is increasingly important as climate change brings high summer temperatures.