What is the difference between Design Pressure, Performance Grade, and Structural Test Pressure
The terms "Design Pressure", "DP," "Performance Grade," "PG," and "Structural Test Pressure," "STP" have in the past been loosely used by some in the field.
The specific definitions of these terms have been carefully confirmed with the publication of AAMA/WDMA/CSA 101/I.S.2/A440-08, NAFS – North American Fenestration Standard/ Specification for windows, doors, and skylights. Those definitions follow:
Design pressure (DP) – a rating that identifies the load, induced by wind and/or static snow, that a product is rated to withstand in its end-use application. (Not to be confused with performance grade (PG) or structural test pressure (STP).) Loads induced by static snow are applicable only to unit skylights, roof windows, and TDDs.
Performance grade (Grade or PG) – a numeric designator that defines the performance of a product in accordance with this Standard/Specification. (Not to be confused with design pressure (DP) or structural test pressure (STP).) Performance grade (PG) is achieved only upon successful completion of all applicable tests specified in Clause 5.
Structural test pressure (STP) – the pressure differential applied to a window, door system, TDD, or unit skylight. In this Standard/Specification, the STP is 150% of design pressure (DP) for windows and doors and 200% of design pressure (DP) for TDDs and unit skylights. (Not to be confused with design pressure (DP) or performance grade (PG).)
In other words, design pressure and structural test pressure are strictly structural qualifications, irrespective of the results of any air leakage resistance testing or water penetration resistance testing.
On the other hand, the performance grade of a product is limited by the lowest/least performance of its structural, air leakage resistance, or water penetration resistance test results; operating force and/or forced-entry resistance requirements may also apply.