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What is Passivhaus?

Passivhaus buildings provide a high level of occupant comfort while using very little energy for heating and cooling. They are built with meticulous attention to detail and rigorous design and construction according to principles developed by the Passivhaus Institute in Germany, and can be certified through an exacting quality assurance process.

 

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.

 

What is the Passivhaus standard? 

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 EnerPHit standard - for refurbishment and retrofit

Passivhaus certification is also possible for very low energy retrofit projects. EnerPHit is a slightly relaxed standard for retrofit projects, where the existing architecture and conservation issues mean that meeting the Passivhaus standard is not feasible.

 

 

Performance targets for a European climate

 

Passivhaus

EnerPHit

Primary energy demand

≤ 120 kWh/m2. yr

≤ 120 kWh/m2. yr + heat load factor

Space heating demand

≤ 15 kWh/m2. yr

≤ 25 kWh/m2. yr

Space cooling demand

≤ 15 kWh/m2. yr

≤ 25 kWh/m2. yr

Specific cooling load

≤ 10 W/m2

≤ 10 W/m2

Airtightness

 ≤ 0.6 air changes/ hr @ n50

≤ 1.0 air changes/ hr @ n50

 

How to achieve the Passivhaus Standard in the UK

To achieve the Passivhaus Standard in the UK typically involves:

  • very high levels of insulation
  • extremely high performance windows with insulated frames
  • airtight building fabric
  • 'thermal bridge free' construction
  • a mechanical ventilation system with highly efficient heat recovery
  • accurate design using the Passive House Planning Package (PHPP)

 

Claiming the Passivhaus Standard in the UK

The Passivhaus Trust recommends that the best way to achieve quality assurance for a Passivhaus project is through certification by a registered Passivhaus Certifier. It is reasonable to claim that a building is a non-certified Passivhaus provided that it still meets the requirements of the standard. Read more about this in our Technical briefing paper 'Claiming the Passivhaus Standard.'

 

 

 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%.

 

 

Certification

The Passivhaus Institute has developed a series of certification processes to ensure the quality of any official Passivhaus buildings and practitioners:

  1. Building design - The Passivhaus Planning Package (PHPP), used to inform the design process and to assess or verify compliance with the Passivhaus Standard.
  2. Designers - Certification for designers who have the expertise to deliver Passivhaus buildings.
  3. Building construction - A certification process for Passivhaus buildings, which applies both to the proposed design and the completed building.

A number of UK organisations have been approved to assess and issue the Quality Assured Passivhaus Certificate. Details of Passivhaus Trust members, partners and staff who can provide certification can be found here.

Certification Process:

Certification Process Flow Chart

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