8.5   Multifamily Buildings


Envelope and HVAC equipment requirements for multifamily apartments in buildings that are four or more habitable stories (and hotels or motels of any number of stories) are covered by the Nonresidential Standards. These are explained in the Nonresidential Compliance Manual. Multifamily apartments in buildings that are one to three habitable stories are covered by the Residential Standards for low-rise residential buildings, which are covered in 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, Title 24 compliance report for each dwelling unit. Floors and walls between dwelling units are considered to have no heat transfer, and may be ignored in performance calculations.

8.5.1    Whole-building Compliance Approach

The simplest approach to compliance for a multifamily building is to treat the building as a whole, using any of the compliance paths described in earlier chapters. In practice, this process is similar to analyzing a single family dwelling, except for some differences in water-heating budgets and internal gains, as described in the 2013 Residential ACM 'Manual.

Multifamily buildings that utilize efficiency measures that require HERS field verification must submit separate compliance documentation for each individual dwelling unit in the building as specified by Reference Residential Appendix Section RA2.3. This requirement does not prevent use of the whole-building compliance approach for submittal of the Certificate of Compliance to the Enforcement Agency, however when the whole-building compliance approach has utilized a measure that requires HERS field verification, a separate copy of the whole-building Certificate of Compliance must be submitted to the HERS provider for every dwelling unit in order to satisfy the requirements of the HERS provider data registry documentation procedures. In practice, the Certificate of Compliance information may not need to be submitted to the HERS provider more than one time, but a relationship must be established in the HERS provider data registry between the whole-building Certificate of Compliance and the corresponding dwelling-specific Certificates of Installation, and the dwelling-specific Certificates of Verification. Thus, for the whole-building compliance approach in a multifamily building that has utilized a compliance option that requires HERS verification, the required energy compliance documentation for each dwelling unit should consist of a whole-building Certificate of Compliance (CF-1R), a dwelling-specific Certificate of Installation (CF-2R), and a dwelling-specific Certificate of Verification (CF-3R).

When the whole-building compliance approach is utilized 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 to the Compliance Software, and dwelling-specific data output from the Compliance Software that must be shown on the Certificate of Compliance, therefore they cannot be properly documented using a single whole-building Certificate of Compliance.

The measures that cannot be utilized for the multifamily whole-building compliance approach, but can be taken for credit when dwelling units are individually modeled as follows:

1.   Buried Ducts credit

2.   Deeply Buried Ducts credit

3.   Reduced Supply Duct Surface Area credit

4.   Maximum Rated Total Cooling Capacity credit

5.   Building Envelope Sealing credit (blower door test)

When the Standards require registration of the compliance documents, the information for the Certificate of Compliance (CF-1R), Certificate of Installation (CF-2R), and Certificate of Verification (CF-3R) must be submitted electronically to the HERS provider data registry. Refer to Reference Residential Appendix RA2 for additional information on these document registration procedures.

8.5.2    Unit-By-Unit Compliance Approach – Fixed Orientation Alternative

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 computer program. In this approach, surfaces that provide separation between dwelling units may be ignored since they are assumed to have no heat loss or heat gain associated with them. Surfaces that provide separation between dwelling units and central/interior corridor areas must be modeled for heat transfer 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. That is, 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. Likewise, end units must be modeled separately from the middle units; and opposite end units must both be modeled. With this approach every unit of the building must comply with the Standards, so this 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


Example 8-2


When preparing compliance calculations for a three-story apartment complex, I have the option of showing compliance for each dwelling unit or for the entire building. If I use the individual dwelling unit approach, do I need to provide calculations for every dwelling unit?


Each dwelling unit must comply with the Standards when using this approach. When dwelling

units have identical conditions, the calculations can be combined. This means you will 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) have little heat transfer and can be disregarded in the compliance calculations.

Note: For multiple dwelling units that is identical in every way except orientation, a single multiple orientation report can suffice or meet the compliance for that unit.

8.5.3    Unit-By-Unit Compliance Approach – Multiple Orientation Alternative

Another option for showing unit-by-unit compliance for a multifamily building is similar to a method that may be utilized for single family master plans in subdivisions (described in Section 8.6).

The computer method may be used to demonstrate that a dwelling unit plan in a multifamily building complies regardless of how it is oriented. To assure compliance in any orientation, the annual energy consumption must be calculated in each of the four cardinal orientations: true north, true east, true south and true west. With this option, a dwelling unit plan must be modeled using the identical combination of energy features and levels in each orientation, and must comply with the energy budget in each case. If a multifamily dwelling floor plan is utilized as both reversed and original/standard floor plan types, either the reversed plan or the original/standard plan may be used to demonstrate compliance, but compliance must be shown in all four cardinal orientations using only one of the plan types.

Each unique dwelling unit plan must be modeled using the worst-case condition for the energy features that the plan may contain within the multifamily building (e.g. highest glazing percentage, least overhangs, largest wall surface area, and with exterior walls instead of party walls if applicable). See Reference Residential Appendix RA 2.6.1 for information that describes how to determine when a dwelling is considered to be a unique model. Each unique dwelling plan must also be modeled separately for each unique floor level (see Figure 8-1).