The clients came to me with a clear brief; to design a very low energy eco house which would significantly reduce the cost of their heating bills, but on a restricted budget.
The decision was taken at an early stage to follow passivhaus principles, whereby a combination of very high levels of insulation, strategies for airtightness and controlled ventilation would allow heated air to stay inside the building for longer.
Timber I-joists were used as the primary structural members which would allow the space between to be fully filled with over 400mm thickness of insulation. Junctions between elements (walls, roof, floor etc.) were carefully detailed and inspected on site to ensure a continuous airtightness layer. Both of these measures, whilst relatively inexpensive compared to the equivalent in standard housebuilding, provide a vast improvement to the energy efficiency.