Slide 49 of 67
- Oriented Strand Board
- Oriented Strand Board (OSB) is made of strands bonded with resins under heat and pressure.
- The figure shows the construction of OSB
- OSB panels consist of four or five layered mats.
- Surface layers consist of strands aligned in the long panel direction. Inner-layer layers consist of cross or randomly aligned strands.
- OSB's strength comes mainly from the uninterrupted wood fiber, interleaving of the long strands or wafers and degree of orientation of wafers or strands in the surface layers.
- Contractors often ask: Can I substitute oriented strand board for plywood sheathing?
- OSB is less expensive than plywood
- UBC states that their strength is the same
- When plywood is specified, no substitutions of the less costly OSB should be made without the approval of the structural designer and local building department.
- OSB takes in water and expands.
- This can cause fasteners to fracture the surface of the sheathing and cause the shear wall to fail prematurely during an earthquake.
- Even though the code recognizes OSB as having the same strength as plywood, many engineers do not like it.
- Legally speaking…
- Professional engineers and architects often design to more than the minimum standards of the building code.
- When they do, their specifications must be followed.
- For example, California law states that licensed architects are not responsible for damages caused by unauthorized changes to their plans or specifications. This provision includes changes made by plan reviewers and building inspectors without the architect’s consent.