Prescriptive & Performance Methods
Prescriptive method for rating performance of the building requires that different product categories meet minimum area rating factors for full certification of the building. Depending on climate zone, prescriptive method can restrict the percentage of glass of each elevation in a building.
Performance method for the building allows an averaging of the building elements and ratings to come up with an overall factor for the building. An example would be that window and door performance can be offset with wall insulating performance. Also, less efficient windows can be combined with more efficient windows for an average to meet the required factor. The performance model allows for the best flexibility in the development of a good building energy plan.