The origins of the EnerPHit standard

Domestic energy consumption (and associated heating cost) is wide ranging: the most efficient Passivhaus accredited building needs only 10 -15 kWh/m²a (kilowatt hours per square metre per year) while an older uninsulated building may need 400 kWh/m²a or more.

If an energy retrofit, or refurbishment of an existing building, meets new build Passivhaus criteria it can become a certified Passivhaus and/or achieve EnerPHit certification as evidence of building quality and fulfilment of specific energy values. However the same features that make the Passivhaus standard attractive for new build may make it difficult to feasibly achieve an energy retrofit as often unavoidable thermal bridges remain.

For this reason, the Passive House Institute (PHI) has developed the “EnerPHit – Quality-Approved Energy Retrofit with Passive House Components” certificate.  This is the EnerPHit standard developed to become an achievable Passivhaus goal for retrofits.

What is the EnerPHit Standard?


EnerPHit is essentially an extremely low energy standard requiring extra high levels of insulation, low thermal bridging, triple glazing, specific levels of airtightness, ideal solar gain as well as summer shading.

The heating demand required to keep a house warm, generally to an indoor temperature of 19°C, is calculated by the Passive House Planning Package (PHPP) developed by the International Passive House Association (IPHA) and the quality of thermal protection of the individual components are indicated in the standard’s certificate.

The EnerPHit standard requires


  • a maximum heating demand of less than or equal to 25 kWh/m²a:

(with Passivhaus, heating demand of 15 kWh/m²a is the target)

or alternatively:

  • the consistent use of Passivhaus components in accordance with the requirements

and with regards to airtightness

  • <1 ach@50Pa (air changes per hour at 50 Pascal pressure).

 (with Passivhaus, 0.6 ach@50Pa is the target)


The EnerPHit+i designation is applied if more than 25% of the opaque exterior wall surface has interior insulation.

Why is the EnerPHit standard important?

If the building stock of the European Union (EU) is to become ‘zero carbon’ (meaning that all industrial sources of CO2 are converted to run on zero carbon emitting energies) by 2050 whilst most buildings are only retrofitted once every 30-40 years, all energy saving retrofits undertaken now should meet the 2050 targets and compensate for those that will not or cannot be retrofitted. The EnerPHit standard is a measure developed to assist in the zero carbon target being reached.

The use ofPassive House components in retrofit scenarios including those designed to meet the EnerPHit standard leads to extensive improvements to thermal comfort, economic efficiency, lack of structural damage and climate protection.

In the pilot phase of EnerPHit, the PHI carried out case studies with economic modelling on the impact of specific energy retrofit measures. They found that building measures, more than renewable technologies, turned out to be the most cost-effective.

Energy savings varying from 75%-90% have been achieved for a large number of EnerPHit projects and give significantly reduced heating costs.

Where can projects be certified to the EnerPHit standard?

Currently only buildings located in the cool moderate temperate climates are being certified to the EnerPHit standard: examples exist in the USA, UK and Ireland.

Temperate climates have warm summers and cool winters with year round rain or snow and may vary from cool temperate to warm temperate.

There are however examples of Passivhaus across the world, including in warmer climates and it is anticipated that certification to the EnerPHit standard will spread accordingly.

The EuroPHit Project

With theEnerPHit Standardas the goal and Passivhaus principles as the basis, EuroPHit applies and shares knowledge on deep retrofits to the often overlooked yet important area of step-by-step retrofits throughout Europe.

Who can certify a building project to the EnerPHit standard?

There are now PHI Passivhaus / EnerPHit experts and accredited certifiers throughout the world.An online certification platform is under development.

How can the EnerPHit standard be achieved?

To obtain the “EnerPHit – Quality-Approved Energy Retrofit with Passive House Components” certificate the criteria published on apply unless otherwise stipulated in the EnerPHit criteria outlined in the PHI document: EnerPHit and EnerPHit+i Certification Criteria for Energy Retrofits with Passive House Components.

The same building measures that are successful in new construction can be adjusted and adapted as necessary in the refurbishment of existing buildings, whether for a ‘deep retrofit’ or ‘shallow retrofit’ scenarios. It is possible to acquire either full or partial EnerPHit certification to suit either scenario. The idea is to encourage people to do the absolute best that they can whenever doing any work on a building.

The following measures have proven to be particularly effective:

  • improved airtightness
  • reduction of thermal bridges
  • improved thermal insulation
  • high qualitywindows
  • ventilation with efficient heat recovery
  • efficient heat generation
  • use of renewable energy sources

Measures should be carried out in consultation with the certifier in such a way that maximum energy efficiency can be achieved provided that for the duration of their life cycle the measures result in a financial net profit under the normally expected boundary conditions for the building owner and users collectively.

Airtightness and thermal bridges represent the biggest challenges to energy retrofits and in particular around eaves details.

Deep Retrofits

Deep retrofitrefers to an energy-efficiency upgrade that achieves dramatic energy savings on existing use of 50 - 90%. It is often promoted as an integrated approach including airtightness, summer overheating and ventilation and not just insulation, although the use of super insulation (lower than 0.15 W/m2K) is common.

Large scale retrofitting is a good way to make deep retrofit more affordable per m2 as whole terraces and building type groups can that allow a collective approach to be taken often in older suburbs and disadvantaged areas.

Deep retrofit needs to be implemented everywhere for the 2050 carbon neutral targets to be reached. 

Shallow Retrofits

Shallow, partial, step by step retrofits are problematic in that earlier measures may prevent or may have to be removed to facilitate later measures, a more expensive and inefficient approach in the long term.

In order to maintain the integrity of the standard partial certification should state exactly what measures were undertaken and how these measures impact the energy performance of the building.

Passivhaus Software and EnerPHit

The Passive House Planning Package (PHPP) can be used to see if the EnerPHit standard can be reached and where a design falls short.  It is a useful design tool to aid in energy retrofit budget spending.

EnerPHit Retrofits and Historic Buildings

Unlike new buildings which can be sequenced to maximise thermal continuity, airtightness and speed, in older, historic buildings, the existence of old walls, intermediate floors, non-ideal orientation and construction methods and historic decorative features, can complicate works and impinge upon the performance possible in energy retrofits.

An additional challenge is to carry out energy retrofits without losing not only the character of the buildings themselves but also of the urban blocks and districts they are situated in, whether or not they are Conservation Areas.

As a result, EnerPHit is considered by many to be best suited for dealing with 20thC building fabric.

EnerPHit and Innovation

Retrofitting to the EnerPHit standard is often coupled with innovative building construction methods and techniques such as externally insulated timber frame walls, overall performance specification and rainwater harvesting.

As the European Commission states,

“…the EU has set itself a long-term goal of reducing greenhouse gas emissions by 80-95% when compared to 1990 levels by 2050….”

As this date approaches, it is expected that Passivhaus building measures will increase worldwide and that governments including that of the UK will have no option other than to roll out large scale energy retrofits to meet the desired target and for now the EnerPHit Standard provides a real solution to achieving the targets set if enough projects strive to meet it.

Qualitape aims to keep you informed of the progress of EnerPHit related developments.


                                                                                                 - Many thanks to Mary Bon RIBA -