Passivhaus at calfordseaden

“A Passivhaus building is one in which thermal comfort can be provided solely by heating or cooling of the fresh air flow (without using recirculation), which is required for good indoor air quality” (Passipedia). This approach has gained popularity worldwide as a sustainable solution for creating healthy, comfortable, and energy-efficient buildings across various climates and building types. Emily Mansfield, Associate Sustainability Consultant and Passivhaus Consultant, discusses the fundamentals, importance, and future of the Standard. 

What is Passivhaus?

Passivhaus is a German standard developed by Dr Wolfgang Feist and Mr Bo Adamson in 1988. The concept was developed as Dr Wolfgang Feist could not understand why energy consumption failed to reduce in buildings with an increased level of insulation.

The Passivhaus standard is based on achieving indoor comfort, applying the fabric first approach to its full extent. With a well-insulated and airtight construction, it is designed to ensure a comfortable indoor temperature is maintained throughout the year by reducing draughts and cold radiant from surfaces. Internal surfaces are to have a minimum temperature of 17^oC, which is important around cold thermal bridges to mitigate the risk of condensation and mould.

Passivhaus also assesses the operational energy use for kitchen appliances, cooking, and elevators. It measures the energy use associated with these additional elements and sets a primary energy target for the whole building.

Why is Passivhaus considered a crucial approach to sustainable and energy-efficient building design?

As we strive to achieve Net Zero Carbon by 2050, it is imperative that buildings being constructed today require as little energy as possible. This is further enforced by planning policies, particularly the Greater London Authority (GLA) London Plan, which requires all new developments to be zero carbon. Upcoming changes to Part L of the Building Regulations and the introduction of the Future Homes Standard in 2025, will also encourage a low energy design with homes being nearly zero energy and future proofed for zero carbon emissions.

These changes in policy encourages the move away from mains gas heating solutions, which has already been experienced where planning policies require the use of low-carbon heating solutions. Heat pumps provide a solution as they operate at a much higher efficiency compared to mains gas boilers and direct electricity. A mains gas boiler may operate at an efficiency of circa 95% whereas heat pumps can operate at a higher efficiency of 300% or higher, significantly reducing energy use and running costs.

Heat loss through the fabric needs to be minimised so that heat can be delivered at a lower temperature, whilst maintaining a constant indoor temperature, to allow the heat pumps to operate at a higher efficiency. Passivhaus requires a well-insulated and airtight construction and sets a low space heating demand target of 15kWh/m²/year, significantly reducing the demand from the space heating system.

In addition to the fabric standards set by Passivhaus, Mechanical Ventilation with Heat Recovery (MVHR) is also required to provide a continuous supply of fresh air to habitable rooms. The other advantage of MVHR is that it recovers heat from the warm wet areas (kitchens and bathrooms) and transfers it to the incoming fresh air via a high efficiency plate heat exchanger, further reducing the space heating demand.

Buildings that achieve Passivhaus certification are third party verified and go under robust testing during design and construction to ensure what has been designed is constructed. Photographic evidence is required throughout the construction phase to demonstrate that insulation has been installed as detailed. MVHR units and other components (e.g. glazing, heat pumps) that have been Passive House Institute certified also go under robust testing. The extensive testing throughout the design and construction phases is crucial to guarantee buildings are constructed to a high standard and perform how they have been designed, helping reduce the performance gap that may be experienced in non-Passivhaus buildings.

How does Passivhaus design contribute to reducing energy consumption?

Passivhaus design looks at balancing the fabric, infiltration, and ventilation losses against the solar and useful internal gains to achieve an energy balance where the space heating demand is minimised. Setting space heating and primary energy targets, focusing on the fabric performance and selection of energy efficient kitchen appliances, offers a low-energy design, significantly reducing the energy requirement within a building compared to the standards set by Part L of the Building Regulations. The thorough testing required throughout design and construction ensures a high standard in performance.

In Passivhaus designs, the orientation and glazing ratios are carefully designed to optimise solar gains during the winter months, reducing the space heating demand, whilst ensuring the risk of summer overheating is minimised. Deep reveals around windows and other forms of strategically placed local shading strategies help reduce solar gains during the summer, with continuous filtered air being supplied through the ventilation system.

The shape and mass of a building also has an impact on the energy performance. A larger building, consisting of a simple shape (e.g. cube), has lower heat loss compared to a smaller building which will require higher levels of insulation to achieve the same space heating requirement. A simple shape also allows floor plans to be stacked, grouping wet rooms (kitchens and bathrooms) and risers together, reducing the length of pipework, wiring and drainage. Not only does this optimise the low-energy design, but it also means less materials are required in the construction, reducing the impact on embodied carbon.

Did you know?

Passivhaus principles can also be applied to existing buildings, applying the EnerPHit standard for retrofit. It helps improve thermal comfort, durability, cost-effectiveness, and energy efficiency of buildings, whilst understanding there are limitations with existing buildings as the orientation and building mass are already in situ.

Role as a Passivhaus Consultant

The role of Passivhaus Designers and Consultants is to assess the design using Passive House Planning Package (PHPP) software to evaluate if it achieves the space heating demand and primary energy targets.

We work closely with the Design Team throughout the design and construction, ideally being involved at an early stage in the design (RIBA Stage 2), advising where the design can be adjusted to provide an energy efficient design that achieves the energy balance. We also offer workshops and presentations, relating to the Passivhaus criteria and principles, as a learning opportunity for all parties.

It is our responsibility to submit the completed PHPP model to the third-party certifier and relevant evidence relating to the assessment for full certification. The qualification is with the Passive House Institute (PHI) as a certified Passivhaus Designers and Consultants. We are required to demonstrate our continued professional development through seminar attendance, self-reading, and project experience.

Passivhaus Projects at calfordseaden

We acted as the Passivhaus Consultant on the award-winning Hartopp and Lannoy Point development. The project consists of the erection of two buildings (Class C3), which will provide 134 new homes, associated parking, and other associated works.

The construction will consist of a well-insulated envelope and air-tight construction, reducing the space heating demand. Appliances will be low energy and hot water demand minimised to help reduce operational running costs. Onsite community heating will provide the homes with low-carbon, affordable heating, and hot water utilising an Air Source Heat Pump (ASHP) only strategy. Solar Photovoltaic (PV) array has been maximised to achieve as close to zero operational CO2 emissions as possible, whilst also reducing the running costs of the ASHPs. The development is to provide low-energy homes via the Passivhaus principles as part of a strategy in which all buildings are anticipated to achieve Classic certification.

As Passivhaus Consultant, we carried out initial studies to determine if the criteria were achievable. This involved hosting regular workshops with the design team to discuss the form factor, balcony and shading strategies, insulation requirements, glazing ratio, and mechanical and electrical services.

The Future of Passivhaus

As we approach the adoption of the upcoming Part L of the Building Regulations and the Future Homes Standard, it is likely the Passivhaus principles will be adopted on schemes to achieve a low-energy design. We are already experiencing this on a number of new residential schemes where it is decided to apply the PHPP software to assess the space heating demand and primary energy, in line with the Passivhaus criteria, even though they are not going for full certification.

With residents at the heart of social housing, there has been an increase in interest in analysing the Energy Use Intensity (EUI) rather than the carbon dioxide emissions savings. The EUI assesses the estimated energy used for both regulated and unregulated energy within the PHPP. The GLA have set a similar target within their Regional Planning Policy – the London Plan, encouraging a low-energy design for all new buildings.

For more information, please contact our Sustainability team if you require guidance and support on your Passivhaus projects.