January 2010. Location: Wherstead, Ipswich, Suffolk

Building description

The building was a converted farm building comprising a timber frame construction with PIR cored insulated roof panels approved by LPCB to LPS 1181 Part 1 Grade EXT-B. The walls were a metal clad built-up system with glass fibre insulation.


The fire occurred in the building services/M&E mezzanine area directly under the roof and involved the combustible services and the timber construction in the area. Based on the charring rate of timber the depth of charring indicated an exposure of the panels equivalent to between 20 and 25 minutes in a fire resistance test.

Photograph 1 shows the extent of charring to the timber at the seat of the fire and the relationship to the panels. Photograph 2 shows a cross-section where the panel has been cut away and illustrates only partial internal charring of the PIR core with the majority of the core unaffected.


The following conclusions can be drawn from the site inspection:

  • The fire was sufficiently intense to have subjected the roof membrane and wall separating the plant area from the retail space to a level of exposure equivalent to approximately 20-25 minutes in a standard fire resistance test.
  • Fire did not spread from the mezzanine plant area to the rest of the building.
  • The PIR core material of the roof sandwich panels did not transmit fire from one side of the walls enclosing the plant area to the other.
  • There was no fire spread within the PIR core