EnerPHit – The Passive House Standard for Retrofits

The Passive House Institute has researched and adjusted the Passive House Standard to the realities of retrofitting buildings considering all the challenges that come with older buildings and developed EnerPHit.

The EnerPHit Standard provides a concept and planning tool that can be used for all-at-once or step-by-step renovations for each project location with their specific climates.

nZEB provides consulting services for deep energy retrofit projects based on the EnerPHit Standard.  We work with our clients to develop an EnerPHit retrofit plan for complete and step-by-step projects.

The key questions that we address are:

  • What are the characteristics of your current building components?EnerPHit Classic
  • Which assemblies must be renewed when?
  • Where are your biggest opportunities to save energy cost?
  • Which retrofit practices are most cost-effective and value-enhancing for you?
  • Where are interdependencies between individual energy efficiency measures and how should they be addressed?

EnerPHit Retrofit Plan benefits:

  • Preparing for future steps already with today’s measures will save costs overall and will ensure an optimal outcome.
  • An excellent outcome can only be achieved if each individual step is implemented with the appropriate quality (EnerPHit-Standard).
  • Once the overall concept has been prepared, it is available for every further step and thus facilitates the planning process (you don’t have to start from the beginning every time).
  • The energy demand is stated for each step.
  • The approximate time points for upcoming refurbishment measures are stated in the general plan. This serves as a valuable aid for personal financial planning.

EnerPHit – The Passive House Standard for Retrofits

Best scenario for a building retrofit is to be performed all at once. The reality for most building owners however, is that it is financially and logistically not feasible to complete an entire deep energy retrofit in one step. In fact, 80-90% of all retrofits undertaken are partial retrofit measures rather than complete one-time deep energy refurbishments. These partial retrofit measures are completed when over time when the respective building component needs to be renewed.

These events are a great opportunity to not just replace an old component, but to improve their performance at the same time. For example, if the facade already needs to be renewed anyway, the extra effort for additional thermal protection of the exterior wall to the Passive House quality at the same time will be manageable.

The challenge is to have these single measures, performed over time, work together to a maximum whole house deep energy retrofit, step-by-step until the last step has been done.

Interdependencies exist between individual energy efficiency measures, e.g. making a building more airtight requires a ventilation strategy. Technical connection details must be developed that will work well during all phases, e.g. how to deal with old windows in a new exterior insulation layer and how to prepare for an optimal window placement once windows will be replaced in a subsequent step.

This is where EnerPHit comes in. Retrofitting existing buildings, it is not always possible to fully achieve the Passive House Standard with reasonable effort. For such buildings, the Passive House Institute has developed the EnerPHit Standard. EnerPHit retrofitted buildings offer almost all the advantages of a Passive House building with optimum cost-effectiveness at the same time.

Passive House Principles

The EnerPHit Retrofit Plan

EnerPHit is a toolset that allows to plan and manage a whole building deep energy retrofit over time, step-by-step. An overall plan will be prepared for the current and all subsequent modernization steps before starting. This is the only way to be sure that everything fits together, and the building owner can count on having a comfortable building with low energy cost over time and once the final step is completed. An EnerPHit Retrofit plan is composed of

  • a scheduler that provides an overview of the chronological sequence of measures that are necessary anyway over the years (e.g. new roof). Appropriate sets of measures can be created for each building;
  • more detailed information about the measures necessary in any case and additional energy saving measures added on;
  • investment, maintenance and energy cost for measures required anyway and additional energy saving measures listed separately;
  • characteristic values of building components used;
  • achievement of EnerPHit criteria;
  • matrix with interdependencies between measures that need to be address at each step;
  • detail drawings and explanatory notes.

The whole EnerPHit Retrofit plan is handed to the building owner for safekeeping. If certification is pursued, all EnerPHit documentation will be stored on the online Passive House Certification platform and can be accessed and updated at each new retrofit step.

The EnerPHit Standard for existing buildings is of course based on the same principles as the Passive House Standard for new buildings, just the set of criteria vary due to the unique challenges of old, existing buildings.

Passive House is the world leading standard in energy efficient construction and it is way more than just a low-energy building. It is a building standard that achieves ultra energy efficient, comfortable, affordable, durable and ecological buildings, regardless of the regional climate.

Passive House is a design and construction concept that can be applied by anyone; it has withstood testing of performance for over 20 years.

For a building to be considered a Passive House building, it must meet a set of criteria, which can be achieved by the following 5 construction principles. These principles relate to new buildings as well as retrofits.

Passive House Principles

EnerPHit and Zero Net Energy – made for each other

To get to zero net energy and beyond, renewable energy has to offset the total energy demand of a building over a year. Heating and cooling energy demand do not tell the whole story of a building’s energy demand, especially in a Passive House the demand for overall household electricity is usually much higher.
Passive House anticipates a future with only renewable energy sources and therefore the total energy demand is calculated in renewable energy only. It takes into account not only renewable energy production but also the challenges of short and long-term storage.
Passive House expresses this demand in PER – Renewable Primary Energy demand.  The PER demand is calculated based on total energy demand of the building, building footprint, renewable energy sources, on- and off-site renewable energy production as well as daily and seasonal fluctuation between energy demand and production based on climate zone.

Like the Passive House Standard for new buildings, EnerPHit provides 3 standard categories:
  • The Passive House Classic, which is the traditional Passive House;
  • The Passive House Plus, in which additional energy is generated, such as from photovoltaics. Such buildings are said to produce about as much energy as residents consume, at least in an – admittedly somewhat misleading – net calculation over the year;
  • In a Passive House Premium, far more energy is produced than needed. This might be a goal for the particularly ambitious building owners and designers who want to go beyond what economic and ecological considerations already propose. The Passive House Institute is working to make the Passive House Standard more attractive for this avant-garde.


A pre-certification can be pursued for quality assurance and recognition. A PHI accredited certifier will check the prepared EnerPHit Retrofit Plan for compliance with EnerPHit requirements, for completeness and consideration of all interrelations between all measures.
This way unnecessary investment and energy cost can be avoided. After approval, the first set of measures can be implemented. Once the step is executed and approved by the certifier the building owner will receive a pre-certification for the building.

A preliminary certificate might increase the value of the building because its potential is clearly demonstrated with 3rd party validation. It also increases the credibility of the refurbishment concept in the context of talks with the bank e.g. because the achievable cost saving is available in a reliably calculated way. Apart from that, you can demonstrate to the outside world that you are committed to climate protection.

Passive House Principles

Deep vs. Conventional Energy Retrofits

A word of clarification about the difference between a conventional and A deep energy retrofit.

A deep energy retrofit is based on a whole-building analysis and construction process to achieve much larger energy savings than a conventional retrofit.

Deep energy retrofits can be applied to both residential and commercial buildings. A deep energy retrofit can result in savings of 50 percent or more, perhaps spread over several years, and may significantly improve the building value, comfort and durability.

Conventional energy retrofits focus on isolated system upgrades (HVAC equipment without impact analysis of possible airtightness and insulation measures ). These retrofits are generally simple and fast, but they often miss opportunities for larger and more cost-effective energy savings, increased comfort and durability.

Of course, the Passive House EnerPHit Standard looks at the whole building as an interdependent system and supports only deep energy retrofits.

Our services cover retrofits that are guided by the Passive House Standard and EnerPHit only.