New research into roof voids has found that a wide interpretation of building regulations and the difficulty of regulating construction work is to blame for inadequate compartmentation, which in turn can lead to greater instances of fire spread.

Compartmentation in Roof Voids (BD2846), which focuses on compartmentation in pitched roof voids for flats at planning and application stage as well as post-fire, was commissioned by the Department of Communities and Local Government (CLG) under the previous government and was conducted by Exova Warringtonfire.

The purpose of the investigation was two-fold: to determine if recent, and current, building practice follows the guidance in the recognised building control regulation Approved Document B, and if not to find out why not; and to conduct research into fires within roof voids.

Investigations from a total of 70 building fires from January to March 2010 were examined, while in a separate part of the report 750 building applications were reviewed for the clarity of their designs. The information was taken from building inspectors, the Butler and Young Group.

Safety officials cited misunderstandings at design and construction stage as common errors - for example, a lack of knowledge about the difference between a cavity barrier and a compartment wall.  A large proportion of applications contained insufficient design detail of roof void compartmentation to allow the inspector to confirm compliance at the plan checking stage.

Communication at design and build stages
A wide variation of construction techniques and a lack of information passing from designer, contractor and the overall inspection process is also a problem, said the report’s author and former fire investigator, Chris Hughes. Monitoring building work is made difficult because an inspector needs to be watching as the roof void is constructed, he said. At present, this is not a statutory notification inspection stage.

Following construction, it can be difficult to verify that the correct measures have been taken because it may require “partial demolition of the wall to check the details fully.”

Fire spread restricted in timber frame building
In cases where compartmentation had been installed correctly, fire spread was considerably reduced. This is true even of timber framed constructions, where it can be typically hard to gain access to cavities to check for fire spread. If compartmentation is adequate, Mr Hughes told info4fire, “the fire is likely to be restricted to where firefighters expect it to [exist].”

One example cited was a four storey block of flats that suffered a severe fire. It was found to have performed very well in terms of compartmentation, with a roof made with breeze block construction. However, the investigation team said that it was difficult to check the cavities of the timber framed building to see whether the blaze had penetrated beyond the compartment.

The key reasons identified for the spread of fire in the study were: combustible materials spanning beneath the non-combustible roof covering; lack of or poor installation of cavity barriers, fire spread along the soffit and heat transfer through penetrations.

Download Compartmentation in Roof Voids BD2846 [pdf]