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 dMEV – Decentralised Mechanical Extract Ventilation. This is individual continuous trickle extract fans in all ‘wet rooms’, with a ‘boost’ function. Each ‘habitable’ room then has a background ventilator in the form of trickle vents in windows or wall mounted vents.
Cost/difficulty
MEDIUM COST – Typically around 5m/m2 for a well designed, installed and commissioned system, including provision of inlet vents in walls or windows, an allowance for new door undercuts to create a transfer path and a small allowance for commissioning to make sure the system is set up properly (according to People Powered Retrofit’s Retrofit options study of a ‘typical’ home in Letchworth).
MEDIUM DIFFICULTY – Can be installed by a competent electrician.
Applicability in Letchworth
Applicable – No specific requirements.
Insights from ASBP
“Comment on breathability and ventilation TBC.”
Case study
Case study TBC
Case study TBC.
Read more
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
This guidance is part of Ventilation
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