Research and analysis

Fire safety: Light gauge steel frame (LSF) walls exposed to fire (executive summary)

Published 22 December 2025

Applies to England

Background

OFR Consultants were engaged by the Department for Levelling Up, Housing and Communities (DLUHC) to deliver the “Real Fires” project (CPD/004/122/039) in support of fire safety technical policy, which commenced on 22nd of October 2021, and will run until the 28th of March 2026. The contract has since been novated to the Building Safety Regulator (BSR), originally formed within the Health & Safety Executive (HSE) and now residing as part of the Ministry for Housing, Communities and Local Government (MHCLG). As part of this project, the contract makes allowance for ad-hoc research to be undertaken to support fire safety technical policy on matters that emerge through dialogue with industry or through observations of real fires. Through this mechanism, OFR have been engaged to undertake research on the fire performance of light gauge steel frame (LSF) walls. 

Executive Summary

LSF wall systems are characterised by three main components: cold-formed steel studs for load bearing, sheathing and insulation materials. Concerns have been raised by industry through Collaborative Reporting for Safer Structures UK (CROSS-UK) regarding the expected fire performance of buildings that employ LSF as a solution for their structural loadbearing system. There is a level of uncertainty arising from the potential exposure of internal and external loadbearing LSF walls to heating conditions on two sides simultaneously, with typical classification testing concerned with one-sided exposure. 

This research project investigated the performance of load bearing LSF walls exposed to fire on two sides and is split into two work packages (WPs) – WP1 and WP2. The first work package (WP1) involved conducting a comprehensive literature review focused on assessing the fire resistance performance of LSF walls when exposed to fire. The review showed that existing experimental and numerical studies have mainly focused on one-sided exposure, and further experimental investigation is needed to understand the structural behaviour of LSF wall systems exposed to fire from both sides. The second work package (WP2) involved generating data and evidence concerning the fire resistance performance of LSF walls under one-sided and two-sided fire exposure. WP2 was arranged into two elements. The first (a) being concerned with fire resistance tests of LSF walls and the second (b) being a subsequent numerical parametric study. 

The fire resistance tests (WP2a) involved benchmark furnace tests on LSF walls exposed to fire on two sides to determine whether the loadbearing performance of LSF walls is likely affected by the number of faces simultaneously exposed to fire. A total of four wall specimens were tested at ITB in Poland, two each (with and without cavity insulation) for one- and two-sided fire exposure conditions under the ISO 834 heating regime. The numerical parametric study (WP2b) involved using validated Finite Element (FE) models to provide an understanding of how different factors influence the thermal behaviour of LSF walls and the potential implications for structural performance. The analysis covered a range of critical parameters, including the nature of insulation, the number of sheathing board layers, the type of fire exposure, and the time lag before the second face of the wall is exposed to fire (representative of fire spread). 

Overall, the study postulates based on temperature profiles that two-sided fire exposure significantly reduces the loadbearing fire resistance of LSF walls compared to one-sided exposure. While cavity insulation (due to thermal gradient) reduces the load bearing fire resistance under one-sided fire exposure compared to no insulation case, its impact is negligible under two-sided fire exposure. Whilst increasing the number of plasterboard layers can mitigate some reduction in loadbearing fire resistance, the overall structural performance is still notably compromised under two-sided fire conditions.

From a technical policy perspective, it is apparent that walls can be exposed to fire on two sides simultaneously in certain conditions and that this can bring about substantial reductions in structural fire resistance of lightweight wall construction. Therefore, the study recommends that consideration should be given to amending Approved Document B to include recommendations for such cases, including fire resistance classification under conditions where two sides of a wall are exposed simultaneously.