Summary
Most existing homes rely on natural ventilation (essentially, opening windows) or intermittent extract fans (e.g. in kitchens and bathrooms) which can be ineffective at ensuring good air movement in all rooms in a home.
Inadequate ventilation can lead to surface or hidden condensation, damp and harmful mould growth. These issues can create poor environmental conditions for occupants and can exacerbate a range of health conditions such as asthma. They can also cause damage to the building fabric/structure (e.g. rot).
A well designed and functioning ventilation system/strategy is key to avoiding these issues. There are a number of ventilation systems available, ranging in cost, complexity and effectiveness. Continuous ventilation is preferred, extracting unwanted, stale, moist air from ‘wet rooms’ (bathrooms, kitchen, utility rooms etc.) and delivering appropriate amounts of fresh air to ‘habitable’ rooms (living rooms, bedrooms, and studies etc.).
One available system is MVHR – whole house Mechanical Ventilation with Heat Recovery. This system includes single central unit with two continuous fans. One extracts stale, warm air from ‘wet rooms’. The other supplies filtered fresh air to ‘habitable’ rooms. This is pre-warmed by passing it over a heat exchanger next to the outgoing stale air. This has great advantages in improved comfort, air quality and heat retention and also noise separation from outside. Due to the need for ducting to every room it is more expensive and can be particularly challenging in retrofit.
Cost/difficulty
HIGH COST – Typically around 65m/m2 for a well designed, installed and commissioned system, including upfront design fee and proper commissioning to make sure the system is well set up (according to People Powered Retrofit’s Retrofit options study of a ‘typical’ home in Letchworth).
HIGH DIFFICULTY
Applicability in Letchworth
Applicable – No specific requirements.
Insights from ASBP
“Comment on breathability and ventilation TBC.”
Case study
Shepherds Barn EnerPHit Plus
A deep retrofit barn conversion to the EnerPHit Plus (Passivhaus retrofit) standard.
Links to further information
- HCCSP Retrofitting Your House Guide (2024), page 23
- Saltaire Retrofit Handbook (2024), page 44
- Retrofitting Your Home – Cambridge Guide (2022), page 21
- The Surrey Home Energy Improvement Guide (2025), page 49
Image credits – 21 Degrees.
This guidance is part of Ventilation
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