Module 6 · Retrofit and Moisture Risk
6.5 Ventilation Strategy Versus Ventilation Product
9 min read
Ventilation is the standard recommendation in damp reports and the standard thing that does not work. A fan is installed, the mould returns, and everyone concludes ventilation was not the answer. Usually ventilation was the answer and what was installed did not ventilate — because moving air out of a room requires air to come in, requires the fan to run when moisture is generated, and requires the occupant to tolerate it.
Learning objectives
By the end of this lesson you will be able to:
- State the conditions required for ventilation to actually remove moisture.
- Distinguish the main system types and what each suits.
- Diagnose why an installed system is not working.
- Specify ventilation that will be used rather than switched off.
Key terms
- Make-up air
- Air entering to replace what is extracted. Without a path for it, an extract fan works against a pressure it cannot overcome and moves very little.
- Background ventilation
- Continuous low-rate provision — trickle vents, passive stack, continuous mechanical extract — as distinct from intermittent boost.
- MEV / MVHR / PIV
- Mechanical extract ventilation, mechanical ventilation with heat recovery, and positive input ventilation. Different strategies with different requirements and failure modes.
- Commissioning
- Measuring installed performance against design flow rates. Frequently omitted, and a system that was never commissioned is a system nobody has confirmed works.
Read the rest of Retrofit and Moisture Risk
Module 1 is open to everyone. The remaining six modules — building science, each damp mechanism in depth, meters and thermal imaging, the full inspection method, and report writing — are free too. We just ask for an email so you can pick up where you left off, and so we can send your certificate when you finish.