CSLB General Building (B)Framing and CarpentryMedium
An engineer specifies a shear wall using blocked plywood panels rather than unblocked panels for the same nail size and spacing. What is the primary structural benefit of blocking the panel edges?
- AIt reduces the number of hold-down anchors required at each end
- BIt increases the allowable shear capacity by fully nailing all panel edges to framing
- CIt eliminates the need for edge nailing entirely
- DIt allows the use of a lower lumber grade for the studs
Show answer & explanationAnswer & explanation
Correct answer: B. It increases the allowable shear capacity by fully nailing all panel edges to framing
Blocking provides continuous framing behind all panel edges (horizontal joints between panels), allowing every edge to be nailed to solid lumber. This increases the wall's rated shear capacity compared to an unblocked wall, where horizontal panel edges are unsupported and cannot be nailed at the specified spacing, reducing load transfer efficiency.
Why the other options are wrong
- A. Hold-down requirements are based on overturning forces, not blocking.
- C. Blocking increases edge nailing capability; it doesn't eliminate the need for it.
- D. Blocking does not change the required stud lumber grade.
Blocked vs Unblocked Diaphragm/Shear Wall
A blocked shear wall has solid lumber backing at all panel edges (including horizontal joints), enabling full edge nailing and higher rated shear capacity than an unblocked assembly.
- Blocking supports horizontal panel joints
- Blocked walls have higher allowable shear values
- Unblocked panels rely only on vertical framing for edge nailing
Memory trick: 'Block it to lock it — full edges, full strength.'