Passive homes have a high level of thermal insulation within their building envelopes (walls, doors and windows). This is a key feature of these buildings; the amount of heat lost is at a minimum level. This results in the home being adequately heated even when it is very cold outside, by simply preheating fresh air that enters the rooms.
What forms of insulation exist?
Insulation can be a form of rigid, spray, attic or natural insulation and this is the most important feature of such a home. Reducing loss of thermal insulation results in savings in energy bills as well as creating a comfortable living environment.
Thermal conductivity is what determines a ‘Passive Home’. Phenolic insulation, fibre glass and rock wool insulation are the most common materials used. These materials will create U values throughout walls, floors and attic spaces and if they are of an adequate thickness they will meet the Passive standard.
Installation of thermal insulation is important, but is often overlooked. Cavity wall insulation, if not installed correctly, can compromise the U values and therefore the effectiveness of the product.
Timber frame wall insulation can sag and if poor materials are used, again the U value requirements may not be met.
Because heat naturally moves from hot to cold, it cannot be stopped but is able to be slowed down to achieve thermal insulation. Heat transfer is the rate at which it moves.
Thermal looping is caused by poor air tightness, such as when an insulated cavity wall has an air gap inside, and will reduce the actual U value by as much as 50%.
With excellent insulation, the passive house’s heating demands is lower than 15kWh/m2, making it less than 90% of average houses.
Achieving the standards required for a Passive home means having a different approach to design and construction.
Passive solar design is one approach that supports this type of energy conservations and works well, by reducing building surface areas and maximising solar energy.
Superinsulation works in eliminating thermal bridges to reduce heat transfer through floors, walls and roofs. In Sweden, insulation thickness is approximately 13”.
Advanced window technology uses high R values with triple pane glazing that is insulated. Low emissivity coatings are applied to reduce thermal transfer.
There are around 15 to 20,000 passive houses today, with the majority having been constructed in Scandinavia. The world’s biggest passive house area is in Heidelberg in Germany.
Image Courtesy: mentalfloss.com