Passivhaus or Not?

Passivhaus is a voluntary thermal comfort and energy standard for buildings. It provides a set of tools and processes to design, build, commission, and hand over a low energy building with high thermal comfort. Passivhaus is widely considered to be one of the world's most rigorous low-energy design standards. The energy targets are consistent with both the LETI and RIBA targets for energy performance of net zero carbon compatible buildings.

Passivhaus follows several key principles:

• Use building physics to design an energy-efficient building (this includes the thermal envelope, glazing, and ventilation systems)
• Reduce the heating demand of the building
• Consider all energy uses, both regulated and unregulated, in the building design
• Use tried and tested energy modelling tools, which allow monitoring of the design throughout the project
• Employ stringent quality control during design and construction

The stringent Passivhaus targets for thermal comfort, heating energy, and overall energy consumption are principally met through:

• Using the building form to reduce winter heat losses and unwanted summer heat gains by passive means
• Providing high performance, well-detailed insulation to minimise cold draughts and heat loss
• Designing and delivering an airtight envelope to minimise cold draughts and heat loss
• Using high performance, triple-glazed windows
• Providing highly efficient services with minimal losses
• Using efficient ventilation units with heat recovery

There are some common details and approaches to these, which are shown in the figure below:

The principles and process are the same for both new-build and refurbishment. The refurbishment flavour of Passivhaus is called EnerPHit, and has challenging but more relaxed targets for airtightness, heating demand, and total operational energy. It can be applied to small and large buildings, with the Entopia project a good example of a larger application in the UK.

Many people worry that Passivhaus buildings are boring, all have the same look, or that it kills creativity. This has not been my experience. A design team who embrace the principles from the outset can create exciting and environmentally responsible architecture.

As Charles Eames said, "I have never been forced to accept compromises, but I have willingly accepted constraints." There's a wide variety of Passivhaus schemes around, including the Stirling prize winning Goldsmith Street, Agar Grove, Lucy Cavendish College, Cranmer Road Student Accommodation, and large non-residential schemes like the Centre for Medicine at Leicester, the Entopia Building, and the George Davies Centre in Leicester.

• Passivhaus is excellent at what it targets: comfort and low operational energy consumption. It's a key ingredient in net zero carbon buildings, but isn't the whole recipe!
• Buildings still need to be designed for low embodied carbon.
• Low-carbon fuels need to be used (Passivhaus encourages the use of electricity over gas, but does not mandate it).
• Designs should use on-site renewables, again this is optional but not essential for Passivhaus.
• Carbon offsetting would still be needed to negate any small remaining CO₂ emissions associated with the building’s operation.
• We encourage soft landings as a way of giving a smooth handover from design to real-world operation.

Our view is Passivhaus is a key element of a built environment that responds to the climate emergency, but it's not enough on its own. The best time to introduce Passivhaus is at the outset of a project. If a project is already underway, the second-best time is now!