2.1 Overview

This chapter describes how the proposed design is modeled and how the standard design is established.

2.1.1 Proposed Design

The building configuration is defined by the user through entries for floor areas, wall areas, roof and ceiling areas, fenestration (which includes skylight), and door areas. Each is entered along with performance characteristics such as U-factors, SHGC, thermal mass, and so forth. Information about the orientation and tilt is required for walls, fenestration, and other elements. The user entries for all these building elements are consistent with the actual building design and configuration. If the compliance software models the specific geometry of the building by using a coordinate system or graphic entry technique, the data generated are consistent with the actual building design and configuration.

2.1.2 Standard Design

For low-rise residential buildings, the standard design building, from which the energy budget is established, is in the same location and has the same floor area, volume, and configuration as the proposed design, except that wall and window areas are distributed equally among the four main compass points, north, east, south and west. For additions and alterations, the standard design shall have the same wall and fenestration areas and orientations as the proposed building. The details are described below.

The energy budget for the residential standard design is the energy that would be used by a building similar to the proposed design if the proposed building met the requirements of the prescriptive standards. The compliance software generates the standard design automatically, based on fixed and restricted inputs and assumptions. Custom budget generation shall not be accessible to program users for modification when the program is used for compliance or when compliance forms are generated by the program.

The basis of the standard design is prescriptive Package A (from §150.1(c) of the standards, Table 150.1-A). Package A requirements vary by climate zone. Reference Joint Appendix JA2, Table 2-1 contains the 16 California climate zones and representative cities. The climate zone can be found by city, county and zip code in JA2.1.1.

The following sections present the details on how the proposed design and standard design are determined. For many modeling assumptions, the standard design is the same as the proposed design. When a building has special features, for which the Energy Commission has established alternate modeling assumptions the standard design features will differ from the proposed design so the building receives appropriate credit for its efficiency. Typically, these measures require verification. Alternate features, such as zonal control, are documented as special features on the Certificate of Compliance. Verified features are also documented on the CF1R.