We are working on an increasing number of projects targeting the Passivhaus and EnerPHit low energy building standards. We use the Passivhaus standard for new build homes and the EnerPHit standard for work to upgrade the performance of existing buildings. 
Achieving EnerPHit standard requires deep retrofitting of the building, and our process begins with an analysis of the existing building and modelling of the possible strategies for the retrofit.
The analysis shows the impact of taking different measures, which allows a more targeted approach and takes into account the unique nature of each project. 
Matt Wickham is a certified Passivhaus designer and member of the Passivhaus Trust.