Achieving Passivhaus Status

Photo courtesy of Daniel Bobker at Thermal Inspections Ltd

Photo courtesy of Daniel Bobker at Thermal Inspections Ltd

In this part of our series of posts about the Passivhaus Standards we examine the exact requirements that are needed for a building to achieve Passivhaus status.

It seems appropriate that, during World Green Building Week, we are looking at the Passivhaus Standards in more detail as building to these standards can reduce the heating energy requirements for a property by a considerable amount. By reducing the heating or cooling requirements of a building less energy is used through the life of the building, making it more sustainable.

To achieve this a building has to meet the Passivhaus Standard. The definition of a Passivhaus is:

“A Passivhaus is a building, for which thermal comfort can be achieved solely by post-heating or post-cooling of the fresh air mass, which is required to achieve sufficient indoor air quality conditions – without the need for additional recirculation of air.”

Basically this means a building where all the heat losses have been reduced so much that it can be heated passively, with the warmth generated from people, household appliances and the sun as well as mechanical ventilation with heat recovery.

The Passivhaus Standard in numbers
This means for the UK that following should be achieved:

  • Space heating demand ≤ 15kWh/m2/yr or space heating load ≤ 10W/m2
  • Space heating cooling demand ≤ 15kWh/m2/yr or space cooling load ≤ 10W/m2
  • Primary energy demand ≤ 120kWh/m2/yr (including hot water, space heating & cooling, fans, lighting, appliances)
  • Airtightness n50 ≤ 0.6ac/gr

The EnerPHit Standard (slightly lower requirements for retrofits) requires the following:

  • specific heat demand of ≤ 25 kW.h/m2/yr
  • primary energy demand of ≤ 120 kW.h/m2/yr
  • roof, wall and floor U–values of ≤ 0.15 W/m2.K
  • windows and doors (including frame and glazing) U–values of ≤ 0.8 W/m2.K
  • thermal bridging psi values to be less than 0.01 W/m2.K
  • whole house mechanical ventilation with heat recovery (MVHR) that is ≥ 75% efficient and exhibits a specific fan power of ≤ 0.45 W.h/m3; and air–leakage of ≤ 1.0 ach at 50 Pa.

But as well as these numerical requirements there is a demanding certification process which has to be gone through during the design and build phases to ensure that the building is certified to Passivhaus standard. The Passivhaus Planning Package (PHPP), a bundle of software and guidance notes, is used in the design phase to ensure that a building will meet the required standards and as part of the certification process.

Find out more about the Passivhaus standards by exploring the other posts in this series and take a look at some of the activities that are going on in World Green Building Week.


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