What is Passivhaus? Everything you need to know

Passivhaus, or Passive House is a building standard that is internationally recognised for energy efficiency, a significantly reduced carbon footprint and provides a comfortable, healthy, and affordable living environment.

To achieve these rigorous standards, Passivhaus requires superior insulation and the use of a mechanical ventilation system combined with design features such as external shading and harnessing solar energy.

The Passivhaus is designed to remain at a constant temperature without the need for heating or cooling to significantly reduce energy requirements.

The background of Passivhaus

The Passivhaus Institute formalised the standards of a Passivhaus, but these principles were built on the ground-breaking work that began in America when there was a critical need to reduce energy consumption.

The term ‘Passive House’ was first used in the 1970s to define a low-energy demand building that harnessed solar energy to create a median internal temperature.

From this early concept began developments of ultra energy efficient ‘superinsulation’ houses:

• 1976 Lo-Cal House
  Designed and built by a group at the University of Illinois at Urbana-Champaign and coined the term ‘superinsulation’. Several houses based on the Lo-Cal design were built in the area between 1977-79.
• 1977 Leger House
  Designed and built by Eugene Leger, in East Pepperell, Massachusetts. It had a more conventional appearance than the "Saskatchewan House", and also received extensive publicity.
• 1977 Saskatchewan Conservation House
  Designed and built by a group of Canadian researchers in Regina. A nearly airtight building with triple-glazed windows and one of the world’s first heat-recovery ventilators.

"What name should be given to this new system? Superinsulated passive? Super-save passive? Mini-need passive? Micro-load passive? I lean toward ‘micro-load passive.’ Whatever it is called, it has (I predict) a big future." - William Shurcliff, American physicist and advocate for energy efficient home design 1979

The superinsulation houses influenced a conversation between Bo Adamson (Lund University, in Sweden) and Wolfgang Feist of the Institut für Wohnen und Umwelt, in Darmstadt, Germany. In 1996, Feist went on to establish the Passivhaus Institute (PHI) and outlined the Passivhaus performance standard.

The standards set in Germany were taken to the US by Katrin Klingenberg in 2002 and The Passive House Institute US (PHIUS) was established. However, the standards from Germany were found to be a challenge to implement in the US, so a different set of standards was outlined by the PHIUS. The PHIUS separated from the PHI in 2012.

Passivhaus now has different bands of climate-specific standards that cover the varying temperature fluctuations around the world. The UK is currently categorised as ‘Cool Temperate’.

The 5 Passivhaus Principles and Standards

To build a home that can be considered a Passivhaus, you need to follow five basic principles during construction. These principles can be implemented when using practically any form of construction system, but they must be carefully followed in order to achieve the measurements expected of a Passivhaus and receive a certification.

The 5 Passivhaus Principles:

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1. Thermal insulation
   All opaque building components of the exterior envelope of the house must be very well-insulated.
2. Passive House windows
   The window frames must be well insulated and fitted with low-E glass filled with argon or krypton to prevent heat transfer.
3. Ventilation heat recovery
   Efficient heat recovery ventilation is key, allowing for a good indoor air quality and saving energy.
4. Airtightness of the building
   Uncontrolled leakage through gaps must be smaller than 0.6 of the total house volume per hour during a pressure test at 50 Pascal (both pressurised and depressurised).
5. Absence of thermal bridges
   All edges, corners, connections and penetrations must be planned and executed with great care, so that thermal bridges can be avoided. Thermal bridges which cannot be avoided must be minimised as far as possible.

The principles of a Passivhaus can be distilled down to three essential features which form the core of Passivhaus design:

• Passivhaus ventilation
  An integrated home ventilation system is required by every Passivhaus. This has to supply, at minimum, a quantity of fresh air needed to maintain a good air quality throughout the home.
  
  A Passivhaus needs to be airtight within its construction, to allow the ventilation system to work efficiently and carefully control the flow of air in and out of the building. Areas with high pollution and humidity, such as bathrooms and the kitchen, have their ‘used’ air removed while fresh air is supplied to the main living areas.
• Passivhaus heating
  For most climates in Central Europe, a highly efficient heat recovery system is required to work in tandem with the ventilation system and a high degree of insulation.
  
  This enables the exhaust air to be filtered through a counterflow heat exchanger to recover heat and transfer that back into the fresh air supply without mixing the airflow.
• Passivhaus windows
  The windows of a Passivhaus play a key role in maintaining the internal temperature and are typically positioned to allow the most natural light to enter the home.
  
  Passivhaus construction required highly energy-efficient windows, with a U-value that’s roughly one-and-a-half times as efficient as that of standard energy saving windows.
  
  To achieve these standards, Passivhaus requires triple glazed windows.

The Passivhaus Standard

Provided a homebuilder has followed the five Passivhaus principles during the building process, the finished house should meet the criteria to be certified as a Passivhaus outlined below:

• The Space Heating Energy Demand is not to exceed 15 kWh per square meter of net living space (treated floor area) per year or 10 W per square meter peak demand.
• The Renewable Renewable Primary Energy Demand (PER, according to PHI method), the total energy to be used for all domestic applications (heating, hot water and domestic electricity) must not exceed 60 kWh per square meter of treated floor area per year for Passive House Classic.
• Airtightness, a maximum of 0.6 air changes per hour at 50 Pascals pressure (ACH50), as verified with an onsite pressure test (in both pressurized and depressurized states).
• Thermal comfort must be met for all living areas during winter as well as in summer, with not more than 10% of the hours in a given year over 25°C.

The latest standards in full can be downloaded here.

The Passivhaus Institute offers a Passive House Planning Package (PHPP) which enables a user to effectively plan, optimise and verify a new build home looking to receive Passivhaus status. Through accurate design modelling within the package, it ensures the new house will meet the expected level of energy efficiency and deliver the required air cooling and draught-proofing measures.

The Passivhaus certification serves to verify that a house does fulfil the criteria by carrying out building tests. You can still follow all the principles and potentially achieve the desired standards without actually being an official Passivhaus, but without the checks carried out for certification, you won’t know whether your building is achieving the energy-efficiency standards you originally set out to meet.

Why live in a Passivhaus?

Considering that heating and energy consumption for buildings is 40% of the UK's total energy usage and a significant contributor to carbon emissions, the Passivhaus principles and standards represent a new type of home that can help combat these emissions.

In response to the pressing issue of climate change, the government introduced a target of net zero emissions by 2050. In 2021, the British Government announced that compliance with the Future Homes Standard (FHS) would become mandatory.

The Passivhaus also offers dramatically reduced running costs for energy bills.

Passivhaus is a choice to not only comply with FHS and to reduce your own carbon footprint, but also the choice for an improved quality of life:

• Energy Efficiency: consuming around 75% - 95% less energy than standard UK buildings, making them a sustainable and environmentally friendly option.
• Low energy bills: Passivhaus buildings have significantly reduced heating and cooling costs compared to traditional buildings.
• Quieter Living: A Passivhaus can be quieter than a standard new-build home, creating a more peaceful living environment.
• Better air quality: Efficient ventilation systems integrated into the building allow pollutants to be removed and maintain a good quality of air throughout.
• Improved health: The continuous supply of fresh air and efficient heat recovery systems contribute to improved health conditions, reducing the risk of respiratory issues and allergies.
• Warmer in Winter: Designed for a median internal temperature and for every internal surface to stay above 17ºc all year round.
• Cooler in Summer: Consideration for window positioning, deeper window reveals, ventilation and shading all avoid excessive solar gain in Summer months.
• Eco-friendly: By reducing energy consumption, Passivhaus buildings contribute to lower carbon emissions, mitigating climate change and reducing the environmental impact of construction.
• Higher Property Value: The energy efficiency, comfort, and quality assurance associated with Passivhaus buildings can lead to higher property values, making them an attractive investment for homeowners

These benefits are all achieved as part of the fabric-first approach of a Passivhaus.

What are the drawbacks of Passivhaus?

While building a Passive House affords plenty of positive features and benefits, there are a few downsides to consider:

• Higher Initial Costs: Building or retrofitting to Passivhaus can be more expensive than constructing a standard building due to the need for high-quality materials and specialised design and construction techniques. The Passivhaus Trust conducted an in-depth report into the additional building costs and found Passivhaus’ best practice costs were around 8% higher than comparable projects.
• Strict Design and Construction Requirements: The Passivhaus standard requires strict adherence to design and construction principles, which can be challenging to achieve and may require specialised expertise.
• Maintenance Requirements: Passivhaus buildings require regular maintenance to ensure that they continue to perform at their optimal level. This includes monitoring and maintaining the ventilation system, changing filters, and ensuring that the building envelope remains airtight.
• Limited adaptability: It can be hard to adapt a Passivhaus. Even small changes to the structure, especially anything that might need to run through a wall like fibre-optic cable, can impact the integrity.
• Potential for Overheating: In some cases, Passivhaus buildings may be prone to overheating, particularly in warmer climates or during heatwaves. This can be mitigated through careful design and the use of shading devices.

Can you retrofit Passivhaus standards to an existing building?

Adapting a structure that’s already been built in order to fit Passivhaus standards can be very tricky, especially depending on how and when the original structure was built. As it’s an existing structure, you cannot realistically change its orientation, window position or shape to properly comply with true Passivhaus principles. This is especially challenging if your property is grade II listed, adding further complications and costs.

EnerPHit Standards for Retrofit Houses

To mitigate retrofit issues, there is a standard called EnerPHit which you can aim for instead. This standard considers the limitations of existing structures and relaxes some of the criteria - while still being a high enough standard to achieve which would outperform many new-build homes for both comfort and energy efficiency. The main differences are for reduced demand for heating and minimal air leakage.

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What needs to be considered is how much more complex a retrofit is to a new build with additional complications. A new home can be carefully planned to comply with the standards at every stage. For a retrofit, every project is different and you have an existing structure to adapt with its own materials and layout. Any underlying problems would have to be fixed, otherwise, your Passivhaus plans could be unachievable or your home could develop deeper, costly issues later down the line.

To help combat this complexity in planning, the EnerPHit step-by-step process has tools to help structure your refit in a way that each phase can be carefully planned from day 1, meaning all aspects can be considered and implemented iteratively.

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Passivhaus developments in the UK

There are plenty of UK Passivhaus developments to be found up and down the country, with the Passivhaus Trust Certified Projects Map being an easy tool to find single homes, multiple dwellings and other buildings which are living up to the Passivhaus standard.

Underhill House was the first development in the UK in 2010 and featured on Channel 4’s Grand Design. Beginning construction over a year prior, this home is built in the Cotswolds Area of Outstanding Natural Beauty and is almost completely hidden from view in the surrounding countryside. Part of the structure is earth-sheltered and highly insulated, while two south-facing sides of the underground home are triple-glazed to minimise heat loss.

Agar Grove is the largest Passivhaus development currently in development. In the London Borough of Camden, a six-phase investment project delivering close to 500 new homes with 348 of them built to the Passivhaus standard. This project is being funded by Camden Council, with 50% of the homes being up for market sale to fund further investment in the community.

A number of new developments are launched each year, and York Council offered a behind-the-scenes tour of their new Passivhaus homes in late 2023.

Hackbridge Primary School won an award in the 2023 UK Passivhaus Awards. As a zero-carbon school, the building has very little energy demand while generating its own renewable energy and offering carefully designed learning spaces to nurture young minds.

Useful Passivhaus resources:

• Passiv Germany
• Passivhaus Trust UK
• Passive House
• Passivhaus UK
• Passive House International
• Passipedia

Commonly Asked Questions