Fire performance evidence must remain representative over time

A recent Swedish LinkedIn post caught my attention. It reports that two SP Fire 105 façade tests have been carried out at RISE in Borås on aged fire-retardant-treated timber façade panels. The panels had reportedly been installed on a building in central Sweden, in different orientations, for three years. Observations from the tests were said to indicate that the façades did not meet the requirements of the test method, with the full report expected before the 2026 summer holiday period.

That report needs to be read before firm conclusions are drawn. However, the issue it raises is already important.

Fire performance is often treated as if it were a fixed property. A product or system is tested, classified, specified, installed and then assumed to continue performing in the same way. In practice, façades are not laboratory specimens. They are exposed to rain, ultraviolet light, temperature cycling, moisture movement, workmanship variation, maintenance decisions and time.

This matters particularly where combustible materials rely on treatment, coating or system detailing to achieve the required fire performance. Fire-retardant treatments can improve the reaction-to-fire performance of timber, but their durability in external exposure conditions is a critical technical issue. The relevant question is not only whether a system passed a test when new, but whether the installed system remains representative of that evidence throughout its service life.

SP Fire 105 is a full-scale façade fire test intended to evaluate the behaviour of an external wall system when exposed to a fire emerging from a window opening. As with all such tests, the details matter. The construction tested, the substrate, cavity arrangement, fixings, joints, treatment, weathering, maintenance history and exposure conditions all influence how the result should be understood and applied.

For designers, specifiers and approving bodies, the lesson is not to panic about timber. It is to be precise about evidence. What exactly was tested? Was the timber treated, coated, aged, maintained or weathered? What exposure condition was assumed? What maintenance regime is necessary? Is the tested system still representative of the building as it will be operated and maintained?

This is where the industry can struggle. Classification can appear definitive, but classification without durability, inspection and maintenance context can give a false sense of certainty. A fire classification is not a general statement that a material or system will perform in all future conditions. It is evidence of performance under defined test conditions, with defined materials, construction and limitations.

The more difficult question is whether fire safety evidence is being managed as a one-off gateway requirement, rather than as part of the continuing safety case for the building. For external wall systems, that distinction matters. A façade is exposed to the environment from the moment it is installed. If its fire performance depends on treatment, coating or careful system detailing, then durability and maintenance are not peripheral issues. They are part of the fire safety argument.

The forthcoming Swedish report will be worth reading carefully. It may prove to be a specific finding about a particular product, treatment, exposure condition or maintenance history. Alternatively, it may point to a broader concern about how the fire performance of treated timber in external wall systems is specified, evidenced and maintained over time.

These are initial observations only, based on information shared publicly before publication of the full test report. Firm conclusions should await the detailed findings, including the construction tested, the exposure history, the condition of the treated timber, the test observations and the criteria applied. Even so, the issue is a useful reminder that fire performance evidence is not simply a point-in-time classification; it must remain valid, representative and maintained throughout the life of the building.