Evaluation of the fall-off of gypsum board in lightweight and mass timber constructions and implications in fire resistance

This review study investigates the fall-off behavior of gypsum board (GB) in Lightweight Wood (LW) assemblies by synthesizing a comprehensive dataset compiled from previously conducted full-scale fire resistance tests. To address the inherent variability and scatter in the existing experimental data, this study incorporates detailed analyses and statistical modeling to discover consistent trends. A few quantitative findings are as follows: adding a second layer of 12.7 mm Type X GB increased the fall-off time to over 60 minutes, improving the fire resistance duration from an average of 50 minutes with a single layer to 68 minutes with 2 layers. On the other hand, insulated floors experienced accelerated GB degradation in 1-layer GB floors. Reducing the resilient channel spacing from 610 mm to 406 mm increased the fall-off time by approximately 10% for 2-layer GB floors. In a single layer of GB, the onset of wood charring was around 10.7 minutes before the GB fell off, while in 2-layered GB floors, the charring began 6.4 minutes after the face layer's fall-off. These findings extend beyond LW systems, offering potential solutions for mass timber (MT) structures where practical and economical GB encapsulation can facilitate fire safety in such structures. This study evaluates the GB protection design equations in international codes showing that these equations are conservative for single-layer GB but within the average range of the experimental results.