In Australia the level of insulation required is obviously less than in Europe, however a high level of insulation is still an absolute fundamental in order to keep heating and cooling energy demands at a minimum. Walls, ceiling and slab insulation all need to be carefully specified to ensure that cost and effort in other areas are not negated by a structure that can’t retain heat.
High Performance Windows
One of the 5 integral features of the Passivhaus for good reason; poor quality or incorrectly specified windows can be a major source of inefficiency. The typical NSW east coast will need windows that have a low U-value and a low to mid SHGC, and, if aluminium framed, will need to be thermally broken. See what these abbreviations mean to the right.
Thermal bridge free
A thermal bridge is where heat has the opportunity to escape/enter by travelling through a material or element significantly faster than the average of all other insulative elements. An example of this may be when an interior floor and an exterior balcony share a continuous suspended slab. If this slab is not “thermally broken” with a structural, low-conductive device (like the image to the right), then it will become a thermal bridge. No matter how well the walls are insulated, in winter heat will ‘leak’ through the slab and into the outdoors. An easier to understand concept may be that the cold creeps into the home via this slab. In summer, the opposite happens, and outdoor heat will creep into the cooled interior.
Aluminium windows are also available in thermally broken designs. A rubber or plastic ‘absorber’ is inserted within the surrounds of the frame like filling in a sandwich. This prevents heat travelling through the aluminium to escape to the colder side. Timber and uPVC windows are non-heat conductive and therefore do not need to be thermally broken. The other benefit to thermal bridging is that you keep the dew point on the outside of your airtight barrier. If elements like a slab are not thermally broken, the dew point shifts within your interior and in winter condensation starts to form within your house.
The airtightness of a Passivhaus is a necessary measure to make sure the only heat flow out of a house is through the ventilation system. See Chapter 2.1.2 Healthy Homes for more information.
Energy Recovery Ventilation (MVHR)
Given the requirement for airtightness it is a necessity to implement a system that will deliver fresh air in the winter when windows cannot be opened. This system should not contribute to heat loss.