Common questions

Which types of building can be certified to Passivhaus?

All buildings! There are standard criteria for all types of residential building, education and teaching facilitites, offices, and supermarkets. Check out this useful guide from the PHI.

Any building has the potential to be certified to Passivhaus, however criteria have not been developed for some uses and may need input from the Passivhaus Institut. Some are already being developed, for example swimming pools and healthcare buildings.

Is it Passive House or Passivhaus?

Who cares?! As long as the building performance meets the requirements! Seriously though, in the UK we typically use the German ‘Passivhaus’ to distinguish it as a separate thing from passive design principles, and because it indicates it can be applied to buildings other than houses. In Ireland ‘Passive House’ is used more often.

Can Etude self-certify a project that Etude design?

No, we use separate certifiers when we are the Passivhaus Designer on a project. This is to ensure we carry out a fully independent quality assurance check we do not have design involvement on projects we certify. Try another certifier.

If we have the choice, we usually prefer to be part of the design team. We still recommend certifying to the Passivhaus standard to make the most of the fixed target and quality assurance process.

Do I have to use Passivhaus certified windows to achieve Passivhaus building certification?

No. As long as all the thermal properties of the window can be proven, and the building can achieve the Passivhaus building criteria, any window product can be used.

The window must achieve an average internal glass surface temperature greater than 16°C, and achieve a surface temperature factor (frsi) of >0.8. Practically, in the UK, this means they must have triple glazing with air gaps >12mm, warm edge spacers, and may require insulated frames.

The designer should also consider whether the window frame and locking mechanism can achieve the required airtightness.

Window evidence required:

  • Window frame thermal performance calculations for each element (i.e. head, jamb, sill, meeting rail) to EN ISO 10077-2.
  • A glass data sheet stating the U-value to two decimal places and calculated to BS EN ISO 673, and the thermal transmission, g-value.
  • A data sheet for the glazing edge spacer showing the ψ-value for the window frame proposed.

This evidence is often difficult to obtain from the manufacturer. Specifying Passivhaus certified windows can significantly reduce the risk of not achieving the required criteria, and make the designer’s life easier!

Do I need thermal bridge calculations to achieve Passivhaus certification?

Passivhaus aims to avoid lots of thermal bridge calculations. Using external dimensions reduces the extra heat loss through junctions (thermal bridges) and builds in some safety factor.

The certifier will review the construction junctions and list any details that need calculations during your first design review. If there is sufficient safety margin in the heating demand calculation they will suggest an acceptable safe assumption wherever possible. However, it is impossible to guess a Psi-value reliably and so  you will need to provide thermal bridge calculations in some situations. For example:

  1. You wish to get a more accurate heat loss figure for a junction that occurs a lot. This would allow you to optimise other parts of the building fabric.
  2. The building relies on low Psi-value assumptions to pass the heating demand requirement and the junctions are clearly a thermal bridge. As a guide reducing the insulation by more than 1/3rd would typically give a positive thermal bridge.
  3. There is a junction that is likely to have high heat loss and where a safe assumption is not clear (typically steel or concrete structural connections through the insulation).
  4. Details that have a potential condensation risk.
  5. You wish to use negative psi-values to demonstrate you meet the requirement. In this case all junctions will need to be calculated (rare).

How many Passivhaus buildings are there?

Last time we looked (October 2020), 1214 homes and 38 non-residential buildings in the UK. Well over 1000 Passivhaus buildings! This is steadily increasing and we haven’t found a way to keep it updated automatically yet. Also see the Passivhaus Trust website.

It is likely that only a small proportion of buildings will ever be Passivhaus Certified, because Passivhaus is hard! It takes effort to achieve the quality and energy efficiency of a Passivhaus and there are many cheaper and less good ways to build.

What proportion of the building needs to be retained to certify to EnerPHit?

There is no fixed definition and it is at the discretion of your Passivhaus Certifier.

The default position is that all buildings should target the full Passivhaus standard. The EnerPHit standard is for buildings where the scope of works or existing context and restrictions mean that this is not economically possible.