A product only achieves a performance grade rating if that product complies with all requirements of the NAFS standard for a certain design pressure corresponding to a maximum expected wind velocity regime at the given geographical location. This is the link between design pressure and performance grade – but the latter goes further by encompassing:
- Structural performance: The pressure applied for structural performance verification is 150 percent of design pressure for doors and windows and 200 percent for unit skylights and tubular daylight devices. This is a test that assesses any permanent damage associated with the assembly;
- Water penetration resistance: The water penetration resistance test pressure, which simulates the force behind wind-driven rain, is generally is based on 15 percent of the design pressure for R, LC, and CW performance classes and 20 percent of the design pressure for AW performance classes;
- Air infiltration resistance;
- Uniform load-deflection test;
- Forced-entry resistance (if applicable);
Below, is the link to a great resource put out in partnership with the Lawrence Berkley Lab in California. Easy to understand information, state guides, case studies, and an impressive glossary of terms are all readily available.
Pictured below is a vinyl window with a low performance grade rating that has bowed.