'Good design is not just about what it looks and feels like, but also about how it works'
Steve Jobs
Passivhaus is a proven system of construction that originated in Germany and guarantees quality, comfort and energy efficiency. Having built and lived in a passivhaus before, we knew that we wanted this second house to be passivhaus too. Beyond that there were two choices to make: whether to build a house that's thermally massive or thermally light (put simply: masonry or timber-frame). The walls and floors of a thermally massive passivhaus are constructed from concrete, which acts as a thermal store, absorbing the heat from the sun during the warmer months and slowly giving it back during the cooler months. The timber frame of a thermally light passivhaus cannot store up the heat in the same way, but it takes much less time and energy to heat than a conventional house and won't lose the heat as quickly.
Our first build, The Autonomous House, was of thermally massive construction and we were very happy with how it performed over the five years that we lived there. The internal temperature remained fairly even (around 21C) for much of the year, only dropping to 17C in the coldest winter months, from mid Jan to Feb. However, with no draughts and cold spots, the house was comfortable even at 17C. We designed it using the Passivhaus Planning Package - complex software into which you enter all of the construction details, as well as data about the location's climate. It calculates how much energy will be needed to heat the house (the details can then be altered if necessary to end up with the desired low figure).
We want to use the same method of construction for this house. It adds an extra level of quality control before, during and after the build; it also adds to the initial cost, unfortunately, but we'll have the satisfaction of knowing that the house is designed and built well, and is energy-efficient and a comfortable temperature all year round.