The Building Safety Regulator (BSR), part of the Health and Safety Executive, published a summary of fire testing on spray foam roof insulation on 22 December 2025. The report covers England and was produced by OFR Consultants Ltd, which was engaged to deliver the "Real Fires" project in support of fire safety technical policy1.
The work was originally commissioned on the 22nd of October 2021 by the Department for Levelling Up, Housing and Communities, with a contract running three years from that date1. OFR attended an online meeting with departmental staff on the 8th of April 2022, where officials relayed industry observations that suppliers were incentivising retrofitted spray applied closed and open-cell polymeric insulation to the underside of dwelling roofs to improve thermal performance1. The concern was that such a retrofit could worsen existing fire safety expectations. Three BS 476-3 roof tests were carried out at the Building Research Establishment between June 2023 and November 20231.
The report states that the extra fuel associated with the insulation could bring about a more severe enclosure fire if ignited, and that the introduction of a semi-permanent fire load increases the likelihood of fire spread across a boundary if the roof covering is penetrated1. However, the ad-hoc classification testing found that even traditional coverings with poor performance, such as very old slate and clay tiles, can achieve the highest levels of roof classification for penetration performance despite the combustible sprayed insulation1.
"No guidance currently exists in ADB that controls the reaction-to-fire classification of bounding surfaces in a roof space."
The report notes that developing such guidance could allow insulation to be encapsulated behind fire protective linings, and that some product literature, including British Board of Agrement certificates, recommends enclosing the insulation behind a plasterboard lining1. It also flags that the test 4 method in BS EN 13501-5 provides no quantitative measure of penetration, meaning high classifications can be achieved through multi-layered roof systems containing large amounts of combustible insulation1.
OFR has not yet received the Building Research Establishment's final consolidated report, so the summary is based on interim information including data logger information, test classification reports, images and observations from attending the tests. A revision is expected once certain details are confirmed1.
Why it matters for households
Spray foam insulation applied to the underside of a roof is marketed as a straightforward way to improve a home's thermal performance, which bears directly on how much energy a household needs to keep warm. The report indicates that the fire performance of the roof changes when such insulation is added, and that this may affect compliance with Building Regulations if the application is considered building work1. For a household weighing up insulation as a route to lower bills and greater energy independence, the findings mean the fire behaviour of the roof assembly, not just its thermal value, is part of the picture. The report also notes that exposed insulation is likely to achieve poor fire growth rate indices and total heat release rates1.
What happens next
A revised report is expected once the Building Research Establishment's final consolidated report is received1. OFR has recommended further research into the relationship between Approved Document B provisions for roof coverings and tested systems, and whether the test 4 method needs refinement to include quantitative indicators of penetration where thick layers of charring insulation may be used1. The report says the compartmentation issue has been highlighted to the BSR as an area for additional work, which the regulator considers best taken forward at a future date as part of a broader piece of work1. No dates for that work have been reported.