5. Eliminate Draughts
Draughts not only make a house uncomfortable, but also take with them large amounts of heat; reducing these to a minimum is a fundamental requirement of Passivhaus. In new, well insulated buildings, the losses in heat due to draughts can be as much or more than the losses through walls, floor roof and windows put together. Making a building airtight (draught free) is not easy, especially in existing buildings. The house is being completely stripped back and a new airtightness layer formed on the inside, in some places with ordinary plaster or concrete, and in others with intelligent breathable membranes. The junctions between elements are critical, as this is where shrinkage and movement cracks can appear, and these will let air out. In these locations, specialist airtightness tapes are being used that have been designed to last. We are aiming for an airtightness of less than 0.6 air changes per hour at a pressure of 50 Pascals, whereas building regulations has a backstop equivalent of approximately 10.