Per BCSI-B4 (Building Component Safety Information): The term “construction loading” is typically used to describe Loads from workers and Building materials on unfinished structure, as, for example, when builders temporarily stack bundles of panel sheathing or gypsum board on installed Trusses during the construction process.”
“Construction Loads shall be placed only on fully restrained and braced structures. Make sure that the Truss assembly is properly restrained and braced according to the guidelines in BSCI-B1 and BCSI-B2.”
“Use extreme caution when placing Construction Loads and only stack reasonable amounts of material.”
“Limit stacking periods to approximately one week unless alternative information is provided by the Building Designer, Truss Designer or Truss Manufacturer.”
The construction load must be applied uniformly and must never exceed the truss designed load. For example, a 4’ x 8’ sheet of ¾” softwood plywood weighs about 61 pounds or 1.9 pounds per square foot (psf). If the floor truss is designed for 40 psf live load, then the number of stacked sheets equivalent to 40 psf is maximum 21. If blocking is used beneath a stack of materials, it should be spaced at no more than 24 in. o.c. to simulate a uniform load.
Wood trusses that have been subjected to over-loading during construction should be carefully inspected by a qualified professional/forensic engineer. Due to the nature of wood, there is no practical way to determine the extent of damage to trusses involved in a situation where they have been over-loaded. An example of this type of damage would be cracks within the wood structure that are undetectable to the eye. In addition, the metal connector plates may become loosened due to over-loading causing a reduction in the strength of the truss and the loads it can support. These may lead to expensive repairs, finishing difficulties, and in some cases to structural collapse. Any repairs for specific damage found on these trusses would only be for the indicated damage and would not guarantee that the rest of the truss is structurally sound.
Please review the BCSI-B4 Summary Sheet for more information. This document provides safe stack heights for several materials and illustrates good and bad loading practices.
For additional information, or if you have questions, please contact the MiTek Engineering department.