The Passivhaus principles by themselves are not prescriptive, so this can cause confusion when assessing buildings against them. If the principles are interpreted relatively loosely, new high-density developments in London often align well with them from the start. This is because many new developments already incorporate key elements, which are aligned with what is listed by the Passivhaus institute as principles:
- Adequate insulation: Minimizes heat transfer through the building envelope.
- High-performance windows: Balance natural light with thermal performance.
- Mechanical ventilation with heat recovery (MVHR): Ensures fresh air while minimizing energy loss from ventilation.
- Airtight construction: Prevents drafts and uncontrolled air leakage.
- Reduced thermal bridging: Careful detailing minimizes heat loss at junctions between different building elements.
These, however, provide only a broad framework, and any stricter interpretation of the principles could mean a different view on whether a development is aligned with them. Additionally, crucial design aspects like building form factor and window-to-wall ratio aren’t explicitly addressed in the core principles but are very significant when approaching Passivhaus certification.
For developers wishing to demonstrate commitment to Passivhaus, modelling the development with PHPP software is a powerful tool to evaluate the building against measurable targets. This exercise can be reasonably expected to show that, even with airtightness levels higher than the required for the Passivhaus accreditation, the building will meet most of the other required targets related to energy use. This eliminates the discussion about intangible principles and solidifies the Passivhaus approach.