US Voluntary Product Standard PS 1-19 Structural Plywood
PS 1-19 is the updated product standard covering the requirements for American plywood intended for structural (loadbearing) use. Download here.
It includes a quality certification programme for APA (and other qualified testing agencies) to inspect, sample and test plywood panels to ensure factory production control at each mill is functioning correctly.
The standard details various grades of structural plywood such as sheathing for roofs, walls and floors, sanded grades and plywood used in concrete formwork. It also includes performance-based test methods and requirements to determine bond, heat resistance and dimensional tolerances for compliance.
It covers wood species, veneer grading, adhesive bonds, panel construction and workmanship, dimensions and tolerances, marking, moisture content and packaging. There are also prescriptive layups using common American species at defined veneer thicknesses, layers and panel thickness.
To confirm to this standard, plywood panels must meet or exceed the following:
Wood species: Acceptable species are defined. This includes American trees as well as those from other parts of the world.
Synthetic repairs: The use of synthetic fillers to repair minor characteristics and their performance must be to the same standard as required for a wood repair.
Veneer Grade: Grades of veneer are identified for manufacturing the plywood (A, B, C, C-plugged & D) with A being the best and D the lowest grade.
Veneers and Layers: The thickness of veneers needed for specific panel thicknesses. This includes parallel-laminated veneers, explaining where they can be used in the manufacturing process.
Panel grades: Provides the permitted combinations for veneer grades to be assembled into various panel grades such as – sheathing, single-layer floor, marine, decorative panels, underlayment, concrete form panels, Structural 1 panels, special exterior and overlays.
Adhesive bond requirements: American structural plywood is manufactured as either an Exposure 1 bond classification or an Exterior bond classification. Both use the same exterior adhesive.
Panel construction and workmanship: The standard sets down exacting rules to cover the construction of all plywood panels, including the minimum number of plies and layers.
- This ensures that the percentage of wood grain which is perpendicular to the panel face grain must be between 33% and 70% of the total panel thickness.
- General rules covering the characteristics prohibited or restricted in certain panels grades are tabulated along with details on sanded, un-sanded and touch-sanded panels. Information on the span rating requirements of panels includes a testing regime covering structural performance is given as are testing qualifications for requirements for panels which are not span rated. Various other aspects of the plywood construction are similarly given.
Dimensional tolerances and squareness of panels: Tolerance levels covering panel sizes, the performance category and thickness requirements, squareness and straightness.
Grade Marking and Certification: This section defines a qualified inspection and testing agency, and gives details on panel marking.
Specimen preparation and testing: The standard sets out testing requirements for –
- The quality of the adhesive bond
- The structural requirements of performance-tested plywood
- Concentrated static and impact loads
- Uniform loads
- Panel bending
- Planar shear strength
- Shear through the thickness strength.