There are three approaches to make an addition comply with the energy code:

• The addition as defined above meets all code requirements. This approach does not require that the original portion of the building meet code requirements.
• If the building combined with the addition complies with the code, the addition will also comply, regardless of whether the addition complies alone. For example, a sunroom that does not comply with the code is added to a house. If the entire house (with the sunroom) complies, the addition also complies.
• In the 2000 and 2003 International Energy Conservation Code, additions less than 500ft² (46.5m²) of conditioned floor area may meet the prescriptive envelope requirements in the table. To use the table, the total area of windows, doors, and skylights cannot exceed 40% of the gross wall and roof area of the addition.

This document describes how to use REScheck™ to comply with approach #1.