Passivhaus: It’s time to tackle indoor air quality in homes

Problems arise then there is not sufficient mechanical ventilation to ensure adequate air exchange and when the choice of finishes and materials specified do not pay attention to off-gassing and VOCs. MVHR ensures a continuous supply of fresh air and the removal of polluted air and excess humidity.

Metrics around mechanical ventilation supply specify a minimum of 30 m3/h.person needed for fresh air requirements, but the sizing of systems is the responsibility of Mechanical Engineers. Buildings may fail to meet their design aspirations due to factors such as poor construction quality, poor commissioning or inadequate occupant training/engagement. Retrofitting buildings can also pose extra challenges around condensation and mould growth if not done properly, and in some cases specialist modelling may be required.

Overheating is a growing issue as temperatures rise and residents struggle to keep cool. Through Passivhaus design modelling you can spot hotspots at design stage and re-orientate or re-design glazing and shading to help keep temperatures even year round. For a recently completed Passivhaus extra care home in Exeter, we used Exeter University’s PROMETHEUS weather data to climate-proof the building to 2080, so it can adapt to changing climates.

UK buildings can perform up to 10 times worse than design predictions, which is referred to as the performance gap. Would you buy a car that only satisfies 70% of its requirements?

The design and construction industry is woefully lacking in evidence around healthy building performance. Without monitoring, how do we know how buildings are performing and how can we all improve? 

Post occupancy monitoring (also referred to as Building Performance Evaluation) is key to ensuring buildings deliver on their promises and design intentions. UK buildings can perform up to 10 times worse than design predictions, which is referred to as the performance gap. Would you buy a car that only satisfies 70% of its requirements? Why do we accept this for buildings?

If industry and clients included wellbeing metrics and building performance evaluation in employers requirements, we would all be much better informed and wouldn’t make easily avoidable mistakes.  Having to demolish or retrofit buildings that are only a few years old to try and make them more comfortable to live in is disastrous for occupants, developers and the planet.

Low-carbon buildings go hand in hand with healthy buildings which need good airtightness along with careful detailing for the removal of draughts, humidity, condensation and mould. Mechanical ventilation with heat recovery provides a continuous supply of fresh air while minimising unwanted heat losses. Controlled ventilation and airtightness are also critical in polluted environments to ensure less pollution and dust.

The specification of natural, biobased materials further promote good indoor air quality by reducing exposure to toxic off-gassing and volatile organic compounds (known as VOCs). Natural materials also have a smaller carbon footprint as they have lower embodied carbon emissions. Finishes such as paints, floor finishes and furniture should be specified for low VOC, as well as  ensuring a good supply of fresh air. We are conducting our own air quality research, with University College London’s Institute for Environmental Design, and have found that even selecting the right cleaning materials make a difference to air quality.

Setting high targets to achieve all this through national policies is key. While there is little evident commitment to this in England, Scotland has been blazing a trail through several exciting policy developments. 

In Scotland from January 2025, all new-build homes will have to meet a new Scottish version of the Passivhaus standard. And the Scottish Futures Trust is linking the funding for all new schools to a metric requiring healthy indoor environment and an energy metric target for a minimum period of 25 years post completion. Funding is released over that 25-year period on the basis of regular reporting on performance to Scottish government. 

Local authorities in Scotland were initially sceptical and surprised that they would have to provide evidence of good internal air quality and low-energy consumption, but the industry has geared up and started delivering these first few projects on site. The Scottish government is now looking at the same for existing buildings, after rolling this out for new buildings. 

There is a lack of technical knowledge both at design stage shown through bad detailing and poor quality construction

Industry must upskill to meet these targets and achieve net zero. There is a lack of technical knowledge both at design stage shown through bad detailing, and poor quality construction. We need to improve our skillsets and share the knowledge, including learnings from previous mistakes. A collaborative, no blame culture is the best way to achieve this. More and better building performance evaluation will also tackle the performance gap. More data on the environmental credentials of materials and building elements (such as Energy Performance Certificates (EPCs) would also help.

But there is hope. We can achieve low-carbon, high-performing and healthy buildings that benefit both residents and the planet. We have the tools and knowledge to achieve this, and the evidence for new-build and retrofits. And we see more and more interest from local authorities, housing associations, developers and clients every day. If we continue the drive together, we can all breathe a bit easier.

Mariam Kapsali is an architect and Passivhaus designer at UK practice, Architype