Passivhaus – also known as passive house – is a leading international low-energy design standard. The concept was developed in the early 1990s by two university professors, Bo Adamson of Sweden and Wolfgang Feist of Germany. The first Passivhaus properties were built in Germany in 1991, since then around 30,000 properties have been built around the world. Passivhaus is increasingly chosen as an effective approach for reducing energy demand and CO2 emissions.
Dr Wolfgang Feist explains what makes a Passivhaus property: “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.”
Buildings designed to Passivhaus standards provide a high level of occupant comfort while using very little energy for heating and cooling, meaning much lower heating bills. They are built with meticulous attention to detail and rigorous design and construction. Structures designed this way can achieve a 75% reduction in space heating requirements, compared to standard practice for UK new build.
Houses that adhere to Passivhaus principles may cost more to build than conventional properties, however experienced Passivhaus designers have managed to build to these principles at no extra cost. Passivhaus-friendly products that may incur extra costs include triple glazed windows, mechanical ventilation systems and thicker insulation. However, whilst extra capital costs can amount to around 8%, heating bills are typically reduced by 90%.
People living in an average UK house might use around 278kWh per m² per year, of which around 140kWh per m² per year would be used for space heating. In Passivhaus a target of 15kWh per m² per year is set as a maximum energy demand for space heating, which is achieved by reducing the heat lost from the building. This is the target because aiming for levels much below this would require a larger additional heating system and the extra cost and complexity that comes with it.
While renewable energy supply systems are a crucial tool for reducing UK carbon emissions, reliance on such systems can add complexity and risk to the real performance of the building. Well-insulated walls, roofs and windows require little attention as they reduce energy demand, and making the structure as airtight as possible will reduce draughts, noise and heat loss.
If you have any concerns about whether Passivhaus is right for your project, the UK’s Passivhaus organisation, Passivhaus Trust, offers an abundance of advice and information. The trust is an independent, non-profit organisation that provides leadership for the adoption of the Passivhaus standard and methodology in the UK.