Why should you aim for Passivhaus?

Passivhaus is an international building code established over 30 years ago in Germany with the intention of creating ‘low-input, high-output’ buildings that are resilient to climate changes and remain comfortable in all seasons. In essence, the building remains stable without requiring large energy inputs (i.e., it is passively comfortable on both hot and cold days) and provides the occupant with a comfortable living environment whatever the weather.

“The heat losses of the building are reduced so much that it hardly needs any heating at all. Passive heat sources like the sun, human occupants, household appliances and the heat from the extract air cover a large part of the heating demand… If such supply-air heating suffices as the only heat source, we call the building a Passivhaus.”

Prof. Dr Wolfgang Feist, Director of the Passive House Institute, Darmstadt, Germany

Buildings are a significant culprit of carbon emissions, accounting for 35% of total global energy consumption. Passivhaus offers a tried-and-tested solution and offers a range of approaches to delivering Net Zero-Ready buildings, both in new and existing buildings. 

In addition, ‘low input’ buildings provide a high level of occupant comfort using very little energy for heating and cooling, making them highly optimised for a decarbonised grid and Net Zero Britain.

In particular, Passivhaus adopts a whole-building approach with clear, measured targets, focused on high-quality construction, certified through an exacting quality assurance process. Passivhaus also manages a slightly relaxed standard for retrofit projects, called EnerPhit, where the existing architecture and conservation issues mean that meeting the full Passivhaus standard is not always feasible.

Much like Building Regulations, Passivhaus has a certain set of stipulated “minimum allowable values” to hit certification, but is actually a far simpler methodology!

As the philosophy of Passivhaus is minimum inputs to sustain comfort, the certification really only has 3 set “metrics” or immovable values in the specification: 

1. Energy required (heating or cooling a building) to maintain the environment
2. Airtightness – ensuring minimal wastage of either heating or cooling
3. Primary Energy requirements – is the energy required coming from renewable sources?

All the other metrics (surface temp, overheating etc.) are a by-product of these core principles, and so too are the design constraints that Passivhaus is well-known for placing on projects.

Example: South-Facing Glass

Large panes of south-facing glass = large ‘solar gains’ in summer, large losses in winter = EITHER:

1. Increase in energy required to maintain environment – FAIL
2. Risk of overheating in building – FAIL

Passivhaus has long recognised that the largest area of lost energy is through unwanted draughts in the building – hence it maintains that any builds must have an air leakage rate of no more than 0.6 Air Changes per Hour at 50 Pascals (ACH50). This is an extremely low level of air leakage and is much tighter than what is required by typical Building Regulations.

Traditionally this level of airtightness has been achieved through large amounts of labour and materials, with time-consuming taping, double checking and confirming leakage at each stage in the process. Hitting airtightness is often one of the main reasons builders are concerned about undertaking a Passivhaus project – not because it’s impossible, but because the check/confirmation only happens at the very end of the project – and can be incredibly costly to resolve

Scientific methods like AeroBarrier aim to eliminate the stress, time, and unpredictable costs of the sealing process. Instead of manually checking and sealing each potential leak, AeroBarrier provides a more reliable approach by only applying sealant where air leakage is confirmed. 

The computer-controlled system operates under positive pressure, similar to inflating a bicycle tyre to find a puncture. When the building is pressurised, AeroBarrier is released as a low-VOC mist. The escaping air pulls the mist toward the leaks, where it attaches and gradually forms an airtight seal. 

The process is continuously monitored to ensure consistent results, with the sealing duration determining the achieved airtightness level. This method is highly resource-efficient as the sealant is only drawn to areas with leaks, ensuring the building meets the crucial 0.6 ACH50 requirement, providing compliance and peace of mind.