Why Ventilation Matters

Without proper ventilation, homes may experience:

• Condensation on windows
• Damp patches or mould growth
• Poor indoor air quality
• Stale or stuffy air
• Increased risk of respiratory problems

As homes become more airtight, ventilation becomes more important, not less.

Surely Ventilation Just Create Draughts?

Yes and no. The key is controlled ventilation, ventilation that occupants can manage and regulate.

Some ventilation openings, such as combustion vents for open-flue appliances, must remain permanently open for safety reasons. Others, such as trickle vents or background ventilation systems, are designed to provide adjustable airflow.

Think About a Winter Coat

If you fully unzip a thick winter coat on a cold walk, you quickly feel the chill and zip it back up. Open it slightly, however, and you allow just enough fresh air to stay comfortable without overheating.

Your home works in a similar way.

Adding insulation is like putting on the coat. It keeps heat in more effectively, but it can also trap moisture and heat if airflow is not managed properly.

Trickle vents and controllable background ventilation act like the zip on the coat, allowing the home to breathe while maintaining comfort.

In this analogy, the person becomes the house.

The person’s activity represents how the property is used, while the coat represents the building fabric and insulation.
Every home behaves differently depending on occupancy, lifestyle, moisture production, insulation levels, and ventilation.

Energy Upgrades and Ventilation Must Work Together

Before insulation or airtightness upgrades:

• Check extractor fans are working correctly and achieving suitable extraction rates
• Ensure vents and air bricks are not blocked
• Confirm adequate airflow exists in loft spaces
• Address any existing damp or mould problems
• Ensure air can move properly around the property

If ventilation is ignored before upgrades, problems often appear afterwards.

Post-Installation Considerations

After insulation or airtightness improvements:

• Check extractor fans remain effective
• Monitor indoor humidity levels (typically 40–60% RH)
• Ensure trickle vents remain open and functional
• Confirm background ventilation has not been blocked
• Watch for signs of new condensation or mould growth

Improved airtightness means ventilation becomes even more important.

Mechanical Ventilation Options

Depending on the level of retrofit or airtightness, properties may require:

• Intermittent extractor fans (IEV)
• Mechanical Extract Ventilation (MEV)
• Positive Input Ventilation (PIV)
• Mechanical Ventilation with Heat Recovery (MVHR)

The correct system depends on the property type, occupancy, airtightness level, and moisture production.

Ventilation Should Never Be an Afterthought

Ventilation should be considered if you are:

• Planning insulation upgrades
• Installing a heat pump
• Improving airtightness
• Experiencing condensation after retrofit works

Make ventilation part of the conversation, before problems begin.