What is a Passive House?
A passive house is designed to have minimal energy requirements for space heating and cooling and have excellent indoor air quality making it extremely comfortable to live in.
Passive House is a fabric first building approach. Super insulated and air tight requiring only a minimal amount of heating, with most of the heat provided by solar gain and incidental gains from showering, cooking and appliances.
A passive house not only has lots of insulation, but careful detailing to eliminate thermal bridging that allows heat to transfer directly through building junctions or gaps in insulation. A passive house must also achieve a very strict level of air tightness to remove heat loss through draughts. Fresh air is then supplied to individual rooms in the house through a heat exchanger, transfering heat energy from the warm, damp stale air extracted from kitchens and bathrooms.
The Passivhaus standard originated in Germany in 1996 and was developed by the Passivhaus Institut (PHI). Gaining Passivhaus certification shows that there has been independent verification that a house meets the passive principals.
The Passivhaus standard
The definition of Passivhaus is driven by air quality and comfort: “A Passivhaus is a building in which thermal comfort can be achieved solely by post-heating or post-cooling the fresh air flow required for a good indoor air quality, without the need for additional recirculation of air.” – Passivhaus Institut (PHI)
“The heat losses of the building are reduced so much that it hardly needs any heating at all. Passive heat sources like the sun, human occupants, household appliances and the heat from the extract air cover a large part of the heating demand. The remaining heat can be provided by the supply air if the maximum heating load is less than 10W per square metre of living space. If such supply-air heating suffices as the only heat source, we call the building a Passive House.”
Univ. Prof. Dr Wolfgang Feist Head of Energy Efficient Construction/ Building Physics at the University of Innsbruck, Austria and Director of the Passive House Institute, Darmstadt, Germany.
Why Passivhaus?
Passivhaus buildings achieve a 75% reduction in space heating requirements, compared to standard practice for UK new build. The Passivhaus standard therefore gives a robust method to help the industry achieve the 80% carbon reductions that are set as a legislative target for the UK Government. Passivhaus also applies to retrofit projects, achieving similar savings in space heating requirements.
Evidence and feedback to date shows that Passivhaus buildings are performing to standard, which is crucial, given that the discrepancy between design aspiration and as-built performance for many new buildings in the UK can be as much as 50-100%.