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. This answer will clarify what the differences are between them.
The biggest difference between U-factor and R-value is that U-factor measures the rate of heat transfer (or loss) while R-value measures the resistance to heat loss. R-value is a measure of conductivity.
There are several terms that homeowners can familiarize themselves with so they can better understand the science behind energy efficient windows like the MI EnergyCore System. They are conduction, radiation, convection, air infiltration, and radiant heat loss.
My city requested that I have tempered glass windows. Is this code for southern California? Or does this meet the safety glass minimal standard?
Local jurisdiction always is the last word for tempered requirements for safety glass.
Standards in the door and window industry are constantly evolving due to changes in technology, building codes and rating system performance requirements. This has led to some confusion around the differences between Design Pressure, Performance Grade, and Performance Class.