A school lesson (roof ventilation) - Build 180(2020)
- A school lesson
- Valid from
- Information provider
- BRANZ Limited
- Information type
- BUILD article
- Website, PDF
BRANZ was called into a Dunedin school where too much ventilation caused excessive condensation in a large roof space. Understanding why this happened points to warm roofs being better in some locations.
Ventilating roofs is generally considered to be a good approach to managing moisture in the roof space and to make the overall roof assembly more robust, reducing the risk of condensation.
A valid question is, can there be too much roof ventilation? We recently saw a school where too much ventilation caused excessive condensation in a large roof space. To find out why this happened, we looked at climatic conditions, location, orientation and building design.
This article includes:
- Building design, orientation, solar gains
- Roof fitted with wind-driven ventilators
- High risk of condensation in this case
- Air condenses on cladding and underlay
- Extractor fan brings in more moist air
- Air barrier may help but not enough
- Even passive vents could be risky here
- Warm roof a better solution here
- Ventilating cold roofs usually helpful