What a Euroclass Does Not Show: Specimen-Level and Between-Campaign Variability in Single Burning Item Testing of Polystyrene-Based ETICS

The reaction-to-fire class printed on the Declaration of Performance of an External Thermal Insulation Composite System (ETICS) is often the only fire performance evidence available during early design. This paper reports, specimen by specimen, twenty-three Single Burning Item tests on nominally equivalent expanded-polystyrene ETICS, performed in one notified laboratory in two campaigns about two and a half years apart. A mineral silicate render on an inert substrate gave a fire growth rate index of 77.3 W/s; a complete ETICS with 100 mm of expanded polystyrene beneath an organically bound render gave 70.6 W/s, so that within the twenty-minute exposure, and while the rendering system retained its integrity, the assembly had a fire growth rate index comparable to, and slightly below, that of the render alone; because the two configurations differ in more than the presence of the core, this bounds the core contribution rather than isolating it. Coefficients of variation between nominally identical specimens ranged from 2% to 87%, and collapse and detachment carry no weight in the class. Individual specimens of one product spanned the B/C boundary, and one assembly was classified as s1 based on a mean of 0.4 m2, below the threshold, although two of its three specimens lay above it. In the later campaign, nominally equivalent assemblies gave mean indices that were 3.7 to 7.0 times higher, with lateral flame spread in seven out of eight tests. The campaigns fall under different editions of EN 13823: the measured burner output places any residual bias of the heat-release chain opposite to the observed change, while the revised smoke correction makes cross-campaign smoke comparison indicative only. The recovered specimen-level dataset, including the time-resolved records, accompanies this paper.