An ID index of 48/24 with blocked edges allows this plywood to span up to 48 inches on which framing member?

• A. Wall studs
• B. Roof rafters
• C. Floor joists
• D. Ceiling joists

Answer: (B)

Understanding how blocking and the panel’s span rating affect how far plywood can span between supports is key here. When edges are blocked, the plywood’s edges are supported, which increases stiffness and helps the panel act as a stronger diaphragm. This allows a larger unsupported span before excessive bending or deflection occurs.

In roof construction, the sheathing spans across the roof plane from one set of supports to the next. With an ID index of 48/24 and blocked edges, the plywood is rated to handle a span up to 48 inches in the direction across those supports, which corresponds to spanning between roof framing members. Roof rafters provide the appropriate continuous support and spacing (often 24 inches on center), making them the framing member that permits this larger span for the panel under these conditions. Wall studs, floor joists, and ceiling joists have different spacing and load paths that generally don’t allow such a long span for this same panel condition.