Sidebar: LEED: A Look at the Rating System That's Changing the Way America Builds
Prescriptive or Performance Approach?
There are two distinct approaches to building guidelines (whether they are mandatory codes or voluntary credits as in LEED): prescriptive and performance-based. Prescriptive credits simply tell the designer what should be done (for example, provide R-20 insulation in walls and R-30 in roofs), while performance-based credits set a goal (for example, total building energy use should be 30% below a given baseline) and leave it up to the designer to determine how that goal is to be achieved. The prescriptive approach is generally easier to use, but it discourages innovation and creativity. With version 2.0, more LEED credits are performance-based than in earlier versions. This shift gives designers more flexibility but also makes it harder to document and verify compliance with the credits.
