Skip to main content

CROSS Safety Report

Rotting of rafters likely due to spray foam insulation

Report ID: 503 Published: 1 July 2015 Region: CROSS-UK

This report is over 2 years old

Please be aware that it might contain information that is no longer up to date. We keep all reports available for historic reference and as learning aids.

Overview

Rafters had rotted in areas to 40-50% of their original depth due to spray foam insulation having been installed some years previously, says a reporter.

Key Learning Outcomes

For construction professionals:

  • Be aware of the risks of moisture and condensation. Whenever insulation is added to a tiled rafter roof, the ventilation requirements must be considered

  • Consider carrying out a condensation risk analysis to ensure the correct form of construction / insulation is detailed to prevent condensation occurring

Full Report

Find out more about the Full Report

Our secure and confidential safety reporting system gives professionals the opportunity to share their experiences to help others. If you would like to know more, please visit the reporting to CROSS-UK page.

The rafters shown in Figure 1 had rotted in areas to 40-50% of their original depth due, says a reporter, to spray foam insulation having been installed some years previously. The spray foam insulation may have been applied due to water ingress from the tiles, lack of ventilation, or both. What was supposed to be retiling of a roof, turned into replacement of all the rafters.

Image
Figure 1: rotten rafters

Expert Panel Comments

Find out more about the Expert Panels

Expert Panels comment on the reports we receive. They use their experience to help you understand what can be learned from the reports. If you would like to know more, please visit the CROSS-UK Expert Panels page.

The public are constantly being pressed to add more insulation in lofts but if this is done without adequate ventilation, the risks of condensation rise hugely. Occupiers sometimes complain of leaking roofs when actually it is condensation in the loft space exacerbated as windows have become more draught proof. The safety risk is that the rot is in structural members that may never be accessed for inspection.

Whenever insulation is added to a tiled rafter roof, the ventilation requirements must be considered. In a traditional construction, ventilation is provided to the roof space to prevent condensation occurring and it may be that the sprayed insulation blocked this. Even in a ‘warm roof’ construction, ventilation is normally needed above the vapour barrier.

Share your knowledge

Your report will make a difference. It will help to create positive change and improve safety.

Our secure and confidential safety reporting system gives professionals the opportunity to share their experiences to help others.