Construction Loads On Floor Truss Assemblies
How much OSB can be stacked on a floor deck without damaging the trusses?
For a typical floor system, material may be stacked up to the point where it produces a uniform loading of 40 psf. Here’s what that means in terms of some common building materials:
Keep in mind that you can assume the trusses will support the design load only when they’ve been properly braced. (See SBCA’s BCSI-B1 Summary Sheet for information on proper bracing.) During the construction process, it is common practice for builders to store stacks of building materials on top of floor truss assemblies. Unfortunately, a check of whether this construction loading causes excessive stresses in truss members is far less common.
Trusses that are overstressed due to construction loading may exhibit loosened connector plates, hairline compression fractures, and excessive sagging. These, in turn, may lead to problems ranging from finishing difficulties to structural collapse.
It is important to realize that in most cases, truss manufacturers design their products to support loads under the following conditions:
- All loading is applied uniformly and does not exceed the design load specified for the component.
- Adequate bracing is in place to ensure that the trusses remain stable and plumb while in service.
If these conditions are satisfied when the truss is loaded with construction materials, then it will not be overstressed. If they are not, then the only way to tell for sure is to redesign the truss for the specific construction loading case.
Keep in mind:
- The combined effect of the live loads and construction loads must never exceed 40 psf. For this reason, do not allow excessive snow to accumulate on the floor deck at the same time as it is loaded with construction materials.
- The construction load must be applied uniformly, just like the design load. If blocking is used beneath a stack of materials, it should be spaced at no more than 24 in. O.C. in order to simulate a uniform load.
- Never stack materials in a location that will produce instability. Stacking materials on the cantilevered portion of a floor truss, for example, is a bad idea. A good rule of thumb is to always stack construction materials between two points of solid bearing.
For more information about construction loading, see SBCA’s BCSI-B4 Summary Sheet.