Passive Roof Ventilation System

A passive roofing ventilation system is a method of ventilating the roof space without using mechanical fans. Instead, it relies on natural airflow – using the principles of convection (warm air rising) and wind pressure differences – to allow hot, moist, or stale air to escape while drawing in cooler, fresh air.

• Humid and/or cold climatic regions

• Warm/skillion roof construction (require particular attention in design and construction)

• Low roof cavity air volume and restricted air movement

• Lack of a vapour control layer (if applicable)

• Low pitched roof or bulk insulation

• Penetrations in the ceiling or warm air entering the roof space

• Activities within the building which create high moisture loading

• High levels of construction moisture such as concrete slab curing

In some region’s condensation risks are higher, such as in areas of cold or high humidity.

Extra care needs to be taken in specifying the correct design and installation practices, as well as building ventilation systems to prevent excessive condensation and moisture in the roof spaces.

Always refer to the latest version of the MRM Code of Practice for the latest best practise in design and installation details. See MRM Code of Practice – Ventilation.

Roof spaces must be designed to avoid moisture-related issues. Ventilation is a key way to achieve that, and while the Code doesn’t prescribe exact vent types or airflow rates, products like ridge vents and battens are all compliant, provided they deliver sufficient airflow and moisture control.

Masons recommends passive ventilation be included in the buildings design to eliminate excess condensation.