The present standards do not consider cases for timber elements covered with fireresistant penetrating coatings and jointed claddings simultaneously. This article is focused on the influence of such combined fire protection on charring depth of studs in timber frame wall assemblies exposed to fire. A key idea was to investigate rather common in local building types of wall assemblies. Wood panels with rabbet joints as cladding with commercially available fire-coating were used for the frame specimens with loose-fill mineral wool filling. The studs were protected also with timber laths which carried the panels forming an air gap
between the cladding and insulation material. Two furnace model scale fire tests were performed in the fire test laboratory of LPNU. Temperature analysis was conducted at control points inside wall assemblies. The calculations according to EN 1995-1-2 are introduced to compare with experimental results. Studies show the impact of investigated coating on the charring rate for studs (150×50 mm), but not for 12 mm wood cladding. Also, using loose-fill mineral wool for insulating tends to char accelerating for the lateral side of studs. The experimental residual cross-section shape considers a faster recession of the wide side surface
due to heat transfer through the insulation. Otherwise, timber laths reduce charring of bottom surface exposed to fire. Therefore, residual cross-section shape is different than the predictable traditional form respectively EN. Despite that, this conservative design approach covered experimental data for residual cross-section of unprotected studs. For fire-coating protected studs, experimental results charring depth is smaller against traditional calculations. That reveals the necessity of further improving computational methods. Wood cladding with rabbet joints fell off almost at the same time (unprotected and protected as well). Possible reasons could be insufficient fire-resistant coatings penetrating in the joint area (covering was performed in-situ), air gaps between wood panels due to the geometry tolerance, air gap between the cladding and insulation material (increasing heat transfer after local fall-off), etc. These issues need to be investigated additionally.
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