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Fires in cavities in residential buildings: the performance of cavity barriers in external walls with combustible materials (NF51)


In recent times there has been significant interest, scrutiny and debate from stakeholders about the risk of fires in timber-framed buildings, with one particular area of concern being the unseen spread of fire within wall cavities and roof voids. This report describes findings from 21 fire experiments which evaluated fire spread in cavities where sheathing materials were included on the structural side. The work showed that properly fitted cavity closers were effective at inhibiting the spread of fire, but that any discontinuities in cavity barriers had a significant adverse effect on performance. The report provides guidance for designers, builders and building control on best practice in the installation and inspection of cavity barriers.

Summary of content

Fires in timber-framed buildings are the subject of significant interest and scrutiny from stakeholders. One of the particular areas of concern is the unseen spread of fires in cavities and roof voids. Fire spread of this nature poses a real challenge for the Fire and Rescue Service, a potential life safety risk and significant property damage risk. There is a growing body of anecdotal evidence that shows that the methods used for the protection of cavities incorporating combustible material are not performing properly in a number of cases.

BRE was commissioned by NHBC Foundation and BRE Trust to investigate fire spread within combustible cavities.This project focused specifically on fire spread within external walls where the cavity between the external fa├žade and the structural frame is incorporated either as a lining material or as a form of insulation (or both) combustible material. In support of this project, an experimental programme was undertaken consisting of 21 experiments involving fires in cavities.