Envelope, HVAC equipment, and outdoor lighting requirements for high-rise multifamily buildings (four or more habitable stories) are covered by the Nonresidential Energy Standards. These requirements are in the Nonresidential Compliance Manual. Indoor lighting in dwelling units and water-heating requirements for high-rise multifamily buildings are covered under the Residential Energy Standards and this manual.
Low-rise multifamily buildings (occupancy group R-1 or R-2) that are one to three habitable stories are covered by the Residential Energy Standards and this manual. Compliance for a low-rise multifamily building may be demonstrated either for the building as a whole or on a unit-by-unit basis. Rental apartment buildings are usually modeled as a whole building. For multifamily buildings designed for dwelling units to be owner-occupied, the project developer may favor providing a separate, unique energy compliance report for each dwelling unit. Floors and walls between dwelling units are considered to have no heat transfer and are treated as interior surfaces in performance calculations.
The simplest compliance for a multifamily building is treating the building as a whole, using the compliance paths described earlier. This is similar to analyzing a single-family residential building, except for differences described in the 2019 Residential ACM Reference Manual.
Multifamily buildings that use efficiency measures that require HERS field verification must submit separate compliance documentation for each dwelling unit in the building as specified by Reference Residential Appendix RA2.3. This requirement does not prevent using the whole-building compliance approach to submit the certificate of compliance to the enforcement agency. For measures that requires HERS verification, a relationship to the whole-building certificate of compliance is made for the corresponding certificates of installation, and the dwelling-specific certificates of verification. Thus, for the whole-building compliance approach in a multifamily building the required energy compliance documentation for each dwelling unit should consist of a whole-building certificate of compliance (CF1R-PRF-01), a dwelling-specific certificate of installation (CF2R), and a dwelling-specific certificate of verification (CF3R).
When the whole-building compliance approach is used for a multifamily building, some of the energy efficiency measures that require HERS field verification cannot be used for compliance credit in the performance calculations. These HERS measures are excluded from the whole-building compliance approach because they require dwelling-specific data input into the compliance software.
The measures that cannot be used for the multifamily whole-building compliance approach, but can be used for credit when dwelling units are individually modeled, include:
•Buried ducts credit.
•Deeply buried ducts credit.
•Reduced supply duct surface area credit.
•Building envelope sealing credit (blower door test).
When the Energy Standards require registration of the compliance documents, the information for the certificate of compliance (CF1R), certificate of installation (CF2R), and certificate of verification (CF3R) must be submitted electronically to the HERS registry. Refer to Reference Residential Appendix RA2.3 for more about these document registration procedures.
The unit-by-unit compliance approach for multifamily buildings requires that each dwelling unit must demonstrate compliance separately. The fixed orientation alternative requires that each unique dwelling unit in the building, as determined by orientation and floor level, must be separately modeled using an approved compliance program. Surfaces that provide separation between dwelling units are treated as interior surfaces and are assumed to have no heat loss or heat gain. Surfaces that provide separation between dwelling units and central/interior corridor areas must be modeled if the corridor area is not directly conditioned or indirectly conditioned space. (See Reference Joint Appendix JA1 for definition.) If the corridor area is conditioned, the corridor area may be modeled separately.
Different orientations and locations of each unit type within the building must be considered separately. A one-bedroom apartment on the ground floor of a three-story building is different from the same plan on a middle floor or the top floor, even if all apartments have the same orientation and are otherwise identical. End units must be modeled separately from the middle units, and opposite end units must also be modeled separately. Every unit of the building must comply with the Energy Standards, so this unit-by-unit approach is more stringent than modeling the building as a whole (See Figure 8-1).
Figure 8-1: Multifamily Building Compliance Option
Demonstrate Compliance for Each Generic Unit Type in Each of its Characteristic Locations
Source: California Energy Commission
Example 8-2
Question
When preparing compliance calculations for a three-story apartment complex, I can show compliance for each dwelling unit or for the entire building. Are calculations for every dwelling unit needed if the individual dwelling unit approach is used?
Answer
No. When dwelling units have identical conditions, the calculations can be combined. Show separate compliance for all unique conditions, such as:
- Front-facing north.
- Front-facing west.
- Front/side walls facing east and north.
- Front/side walls facing east and south.
- Middle units and both end units.
- Exterior roof, no exterior floor.
- Exterior floor, no exterior roof.
Surfaces separating two conditioned spaces (such as common walls) are modeled as interior surfaces.
Note: For multiple dwelling units that are identical except orientation, a single multiple orientation report can be used to demonstrate compliance. (See Section 8.7.2 below.)
Another option for unit-by-unit compliance for a multifamily building is the multiple orientation alternative. This is similar to the method that may be used for single-family master plans in subdivisions (described in Section 8.7).
The performance method may be used to demonstrate that a dwelling unit plan in a multifamily building complies regardless of orientation. To ensure compliance in any orientation, the annual energy consumption must be calculated with cardinal orientation (a combined CF1R with results for north, east, south, and west). With this option, a dwelling unit plan must be modeled using the identical combination of energy features and must comply with the energy budget in each orientation. Cardinal compliance can be used to show compliance for a reversed floor plan.
Each unique dwelling unit plan must be modeled using the worst-case condition for the energy features that the plan may contain within the building (for example, highest glazing percentage, least overhangs, largest wall surface area, and with exterior walls instead of party walls, if applicable). See Reference Residential Appendix RA2.6.2 for information that describes how to determine when a dwelling is a unique model. Each unique dwelling plan must also be modeled separately for each floor level.