1.6 Mandatory Measures and Compliance Approaches

In 'addition to the mandatory measures (Section 1.6.2), the Standards provide two basic methods for complying with low-rise residential energy budgets: the prescriptive approach and the performance approach. The mandatory measures must be installed with either of these approaches, but note that mandatory measures may be superseded by more stringent measures under either approach.

1.6.1    Approaches

A.   The prescriptive approach, composed of a climate zone dependent prescriptive package (Section 1.6.3) is less flexible but simpler than the performance approach (Section 1.6.4) Each individual energy component of the proposed building must meet a prescribed minimum efficiency. The prescriptive approach offers relatively little design flexibility but is easy to use. There is some flexibility for building envelope components, such as walls, where portions of the wall that do not meet the prescriptive insulation requirement may still comply as long as they are area-weighted with the rest of the walls, and the average wall performance complies.

B.   The performance approach (Section 1.6.4) is more complicated but offers considerable design flexibility. The performance approach requires an approved computer software program that models a proposed building, determines its allowed energy budget, calculates its energy use, and determines when it complies with the budget. Compliance options such as window orientation, shading, thermal mass, zonal control, and house configuration are all considered in the performance approach. This approach is popular with production home builders because of the flexibility and because it provides a way to find the most cost-effective solution for complying with the Standards.

C.   For additions and alterations, see Chapter 9 for details of compliance approaches that are available.

1.6.2    Mandatory Measures

With either the prescriptive or performance compliance paths, there are mandatory measures that must always be installed. Many of the mandatory measures deal with infiltration control and lighting; others require minimum insulation levels and equipment efficiency. New for the 2013 Building Energy Efficiency Standards are mandatory measures that require HERS verification for duct sealing and leakage, HVAC system airflow and fan efficacy, and ventilation systems (including exhaust fans) installed to meet the requirements of ASHRAE Standard 62.2. The minimum mandatory levels are sometimes superseded by more stringent prescriptive or performance approach requirements. For example, if mandatory measures specify R-30 ceiling insulation and the prescriptive approach, Package A, is used, R-38 ceiling insulation (depending on climate zone) must be installed. Conversely, the mandatory measures may be of a higher efficiency than permitted under the performance approach; in these instances, the higher mandatory levels must be installed. For example, a building may comply using the performance computer modeling only R-7 insulation in a raised floor, but R-19 must be installed because that is the mandatory minimum.

1.6.3    Prescriptive Package A - §150.1(c)

The prescriptive requirements are represented in Package A. The prescriptive package is the simplest but least flexible compliance path. Package A establishes the stringency of the Standards for the performance approach. Approved computer programs model a house with the features of Package A to determine the envelope, space conditioning, and water heating budgets.

The prescriptive package is a set of pre-defined performance levels for various building components. Each building component must meet or exceed the minimum efficiency level specified in the package. For the 2013 Standards, there is only one prescriptive package: Package A. Packages C and E were eliminated in the 2013 Standards and Package D has been renamed as Package A.

A.   Package A is presented in Table 150.1-A (and its footnotes) in the Standards (also in Appendix B of this document). Package A. The Package A prescriptive requirements serve as the basis of the standard design in the performance approach and determine the energy budget of a proposed design. These prescriptive requirements require that ducted split system and packaged air conditioners or heat pumps (for definition see Reference Joint Appendix JA1) be diagnostically tested to verify that they have the correct refrigerant charge.

1.6.4    Performance Approach

The performance approach, also known as the computer method, requires that the annual Time Dependent Valuation (TDV) energy be calculated for the proposed house and compared to the standard TDV energy budget. TDV energy is the “currency” for the performance approach. TDV energy not only considers the type of energy that is used (electricity, gas, or propane), but also when it is used. Energy saved during periods when California is likely to have a statewide system peak is worth more than energy saved at times when supply exceeds demand. Reference Joint Appendix JA3 has more information on TDV energy.

The use of Energy Commission approved computer methods represents the most detailed and sophisticated method of compliance. While this approach requires the most effort, it also provides the greatest flexibility. The computer program automatically calculates the energy budget for space conditioning and water heating. The budget is determined from the standard design, a computer model of the building using the Package A prescriptive package. The computer software allows manipulation of the proposed building’s energy features to achieve or do better than the standard energy budget; i.e. the building proposed energy consumption would be equal to or less than the standard energy budget.