California Residential Inspector Practice Exam

What is the maximum allowable span for Douglas fir-larch #2 ceiling joists spaced 12 inches on center in an uninhabitable attic without storage using a 2x6" member?

1. 15'-0"

2. 17'-4"

3. 19'-6"

4. 21'-0"

The correct answer is: 19'-6"

The maximum allowable span for ceiling joists is determined by various factors, including the species of wood, the grade of the lumber, the spacing between joists, and the intended use of the space above. For Douglas fir-larch #2 grade lumber when used as ceiling joists, the span is typically governed by its structural strength and the load it needs to support. In the case of 2x6 ceiling joists spaced 12 inches on center in an uninhabitable attic without storage, building codes and engineering tables provide clear guidelines. For this specific configuration, a span of 19 feet 6 inches is permissible due to the inherent properties of Douglas fir-larch, which includes its strength and stiffness characteristics. This maximum span is calculated considering factors such as the limited live load since the attic is uninhabitable, which reduces the stresses on the joists compared to habitable spaces. The absence of storage in the attic further minimizes potential loads. As a result, the 19-foot 6-inch span is within safe limits for the intended use, ensuring that the structural integrity is maintained while also adhering to safety standards. Other options reflect lengths that exceed the established span limits for this specific application, thus not meeting the criteria outlined