This report contains measurements, observations, and results from 30 experiments with fire in the cavity between the wood cladding and the wind barrier. The experiments were performed at RISE Fire Research's laboratory in Trondheim in 2021.

The various experimental setups have been done in a way that is meant to represent typical constructions in Norwegian houses with wooden cladding. All walls were flat, with cladding without gaps or openings and without internal corners, extruding parts, doors, windows, or other penetrations. In most experiments, measures were taken to shield the outside of the cladding from exposure to the initial fire. In several experiments, however, the fire also established itself on the outside of the cladding after it had burned through the cladding from the inside. Large-scale experiments have also been carried out, where both the cavity and the front of the cladding were exposed to the initial fire.

The experiments' results show that the use of royal oil-treated cladding had no statistically significant effect on how the fire in the cavity spread.

The results indicate that the use of the used wind barrier with reaction to fire classification F led to faster flame spread and temperature rise than the used wind barrier with fire classification A2 did, but this is not statistically significant and may be due to random variations.

Experiments with vertical lathing showed faster temperature rise in the cavity than experiments with cross-lathing. This means that the heat spreads faster upwards in the cavity when it forms continuous vertical channels than where the cavity is connected both horizontally and vertically between the cross-lathing. In the cavity with cross-lathing, on the other hand, the heat and fire spread to a greater extent laterally than in the cavity with only vertical lathing.

The fire in the cavity was in many of the experiments limited by oxygen supply. This shows that the supply of air in the cavity can be as crucial for delimiting the fire spread as the fire properties of the materials inside the cavity. When the cavity fire is delimited by the oxygen supply, higher amounts of combustible gases will be formed in the smoke. This can cause the fire to spread to other places if this gas can be ignited.

Full report in Norwegian with English summary (pdf).