Apart from meeting all applicable mandatory requirements (Section 9.4), additions and alterations must demonstrate compliance using the prescriptive or performance approach.
There are several compliance paths depending on the scope of work:
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Addition only: No changes are made to the existing building except removal of roofs, exterior walls, fenestration, and floors required as a result of the addition.
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Alterations only: There is no addition (no increase in conditioned floor area and volume or adding conditioning to a previously unconditioned space).
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Addition and alterations: There are additions and alterations to the existing building.
For each of these permit scenarios, Table 9-1 summarizes the available compliance approaches for single family residential additions and alterations.
Project Scope | Prescriptive Approach | Performance Approach1 |
1. Alteration only: | Meet all applicable requirements for prescriptive alterations | Existing + Alterations without third party verification of existing conditions; or Existing + Alterations with third party verification of existing conditions; or Existing + Alterations as all newly constructed buildings |
2. Addition only: | Additions ≤400 ft²; or Additions >400 ft² and ≤700 ft²; or Additions >700 ft² | Addition Alone |
3. Addition and existing combined (with or without alteration): | Meet all applicable requirements for prescriptive alterations (if any) and a prescriptive addition approach (see additions only above) | Existing + Addition + Alterations without third-party verification of existing conditions; or Existing + Addition + Alterations with third-party verification of existing conditions; or Existing + Addition + Alterations as allnewly constructed buildings |
1 In the performance approach, the building must be modeled with Energy Commission-approved compliance software, as explained in Chapter 8 of this manual. | ||
Regardless of the compliance approach selected, the following exceptions apply:
- Additions of ≤ 300 ft2 do not require a cool roof product (if required by §150.1[c]11) to be installed.
- Whole-house fan (or ventilation cooling) does not apply to additions of 1,000 ft2 or less (if otherwise required by §150.1[c]12).
- Existing space conditioning systems that are extended to provide conditioning to an addition are not required to meet the Energy Code (§150.2[a] Exception 4).
- Indoor air quality (IAQ) requirements (§150.0[o]1C, D, or F) do not apply to additions of 1,000 ft2 or less that are not a new dwelling unit.
- Photovoltaic (PV) requirements do not apply to additions or alterations.
- Heat pump space conditioning requirements do not apply to additions or alterations.
- Addition Alone
In this compliance scenario, the addition alone is modeled using compliance software, and the existing building is not modeled. This approach can work well when the existing building is not undergoing alterations, and the permitted work scope covers only the addition.- Advantages: Little information about the existing building is needed (conditioned floor area, number of bedrooms) because it is not modeled.
- Disadvantages: Some prescriptive allowances for additions do not apply to the addition-alone compliance approach. For example, a 400 ft2 addition has a 30 percent fenestration area limit if complying using existing + addition, while only 20 percent is allowed when complying as an addition alone. Also, with this approach, alterations to the existing building that improve its energy performance cannot be used to “trade-off” requirements for the addition.
- Existing + Addition + Alteration
In this compliance scenario, the entire building undergoes the compliance analysis, and unaltered building components are not required to be brought into compliance.- Advantages: This approach offers the most flexibility by modeling improvements to the existing building. The energy budget provides more generous fenestration allowances for prescriptive compliance.
Note: There is no requirement to make alterations to - Disadvantages: Plans and data for the existing building are needed, increasing the time and complexity of the calculations.
- Existing + Addition as a Newly Constructed Building
In this compliance scenario, modeling the existing building and the addition as if they were a newly constructed building. This approach is used when changes to the existing building are extensive. Demonstrating compliance can be difficult because all existing features must be brought up to current code.
When a single-family building project that includes an addition and alterations uses the prescriptive approach to compliance, all prescriptive requirements must be met. The addition complies with the CF1R-ADD-01 prescriptive certificate of compliance.
Alterations to the existing building must also meet prescriptive requirements and be documented by a CF1R-ALT-02 prescriptive certificate of compliance for alterations.
The performance approach to projects that include both an addition and alterations to an existing residential building is called “Existing + Addition + Alterations.” (See Section 9.5.2.) Projects can comply with or without the benefit of pre-construction third-party inspection and verification of existing conditions that are to be altered.
Alterations may comply prescriptively by meeting all applicable requirements in §150.2(b), which are explained further in Section 9.4. Several prescriptive alteration requirements or exceptions are specific to conditions such as building climate zone.
It is important to note that the energy budget is based on prescriptive requirements and every applicable prescriptive requirement must be met; otherwise, the building must comply using the performance approach. However, if one or more proposed alterations do not comply prescriptively, other alterations must exceed prescriptive requirements for the project to comply based on the performance approach.
Under the prescriptive approach to alterations, the CF1R-ALT-02 prescriptive certificate of compliance is completed and submitted with the permit application. If any mandatory or prescriptive features require HERS verification (see Section 2.5, HERS Field Verification and Diagnostic Testing, of this manual), the certificate of compliance must be completed and registered online with a HERS provider (see Section 2.3 of this manual) before being submitted to the enforcement agency.
Alterations may comply using the performance approach by meeting the requirements in §150.2(b)2. This is explained in Section 9.5. The main options are:
- Existing plus alterations: If multiple components or systems are being altered or if the proposed modification(s) exceed prescriptive requirements, then the existing + alterations performance approach can be used to make trade-offs.
- Compliance without third-party verification: This option allows alterations to comply without third-party inspection to verify existing conditions being altered.
- Compliance with third-party verification: This option allows for alterations to comply only with third-party inspection to verify existing conditions being altered.
- Existing plus alterations as a newly constructed building: This option is the most difficult.
When an addition is built with a connection to an existing wood-framed wall, an extension to an existing wood-framed wall (Figure 9-1) is allowed to retain the existing dimensions (§150.2(a)1Ai or 150.2(a)1Biii). Retain the dimensions means two things: (1) if the existing wood-framed wall has no continuous insulation, the extended wall also does not require continuous insulation; and (2) the existing framing size may be kept.
This exception will typically apply to only one or two walls of an addition. Prescriptive compliance for the walls that meet the criteria will require R-15 cavity insulation if the existing framing is 2x4 or R-21 cavity insulation if the existing framing is 2x6 for the extended wall(s). The energy budget for performance compliance will match the prescriptive requirements.
Similar to a wall extension is a provision that applies to existing wood-framed walls of a previously unconditioned space. If the existing exterior siding (or cladding) of the structure is not being removed, and the space is converted to conditioned space, §150.2(a)1Aiii or 150.2(a)1Bvi requires only cavity insulation of R-15 in a 2x4 wall or R-21 in a 2x6 wall.
Figure 9-1: Wall Extension
New wall is an extension
New wall is not an extension
The California Department of Housing and Community Development defines accessory dwelling units as:
- an attached or detached residential dwelling unit which provides complete independent living facilities for one or more persons. An ADU shall include permanent provisions for living, sleeping, eating, cooking, and sanitation on the same parcel as the single-family dwelling is situated.
The 2022 Energy Code adds a new definition for junior accessory dwelling unit (JADU). A JADU is a dwelling unit that is no more than 500 square feet in size and contained entirely within an existing single-family building. A JADU includes a kitchen, a separate entrance from the main entrance to the building, and an interior entry to the main living area. A JADU may include separate sanitation facilities, or may share sanitation facilities with the existing single-family building.
State legislation that took effect on January 1, 2017, gave more flexibility to build ADUs, sometimes called “granny” or “in-law” units. For compliance, an ADU may be either an addition or a newly constructed building. See Figure 9-2 to determine the compliance requirements. Although the Energy Code that applies to the ADU may be the same as an addition, this may not be the same for other Parts of Title 24. Check with your local building department to confirm applicable requirements.
ADU compliance requirements are based on the associated Energy Code classification as either an addition or alteration to an existing residence or as a new building, as shown in Figure 9-2 . An ADU may comply using any of the prescriptive or performance method options available for other residential additions or new buildings plus meeting applicable mandatory requirements.
- If the ADU shares common walls with the existing dwelling unit and is newly constructed, some of the walls may be wall extensions (Section 9.3.4).
- If the ADU shares no common walls with the existing dwelling unit (detached) and is converting an existing unconditioned structured into conditioned space, an exception to the requirement for continuous insulation is available for walls where existing exterior siding (or cladding) is not removed.
- If the ADU shares common walls with the existing dwelling unit and is converting an attached unconditioned space into conditioned space, the existing walls of the new ADU may meet an exception to the requirement for continuous insulation if exterior siding is not removed.
- If the ADU shares no common walls with the existing dwelling unit (detached) and is a new structure, this is a newly constructed residential building.
Figure 9-2: ADU Types
Addition: Converting existing unconditioned space, attached to existing home. Walls may qualify as “existing wall with siding.” (See Section 9.3.4 for wall exceptions.)
Addition: Converting existing unconditioned space, detached from existing home. Walls may qualify as “existing wall with siding.” (See Section 9.3.4 for wall exceptions.)
Addition: Newly constructed, attached to existing home. One or more walls may qualify as wall extensions. (See Section 9.3.4 for wall exceptions.)
Newly Constructed Building: Newly constructed and detached from existing home.
Addtion: Newly constructed ADU on top of existing detached garage or side-by-side with existing detached garage
Newly Constructed Building: Newly constructed ADU attached to existing home by breezeway, or covered walkway
- HVAC
When adding an attached ADU to an existing home, the Mechanical Code does not allow return air from one dwelling unit to be discharged into another dwelling unit through a shared heating or cooling system. Systems without ducts are an option.
A system serving an ADU must have its own thermostat. Heating systems must be capable of maintaining 68 °F at a point three feet above the floor and two feet from the exterior walls in habitable rooms. Heating and cooling load calculations will need to be provided per Title 24, Part 6, Section 150.0(h) to verify that any existing and/or new system is properly sized,
Any addition that adds a new dwelling unit must meet all applicable IAQ ventilation requirements of Sections 150.0(o)1C, except for additions that are JADUs (defined above). A detached ADU must meet all applicable IAQ ventilation requirements of Sections 150.0(o)1C. An attached ADU must also meet all requirements if the dwelling units do not share a floor or ceiling. The whole house ventilation airflow is to be based on the square footage of the new dwelling unit.
Local exhaust for bathrooms and kitchens is required for any addition. See Table 9-7 in Section 9.4.2 for a more detailed summary of prescriptive HVAC system requirements for additions. - Photovoltaics (PV)
Solar electricity generated by photovoltaics (PV) is not required if the ADU is an addition. PV is required for detached, newly constructed ADUs.
Example 9-4:
Question:
An existing single-story residence has a 600 ft² attached unconditioned storage room that the owner plans to turn into an accessory dwelling unit. The existing uninsulated walls have 2x6 wood framing, and the owner plans to keep the existing exterior siding. For prescriptive compliance, what wall insulation is required in the proposed ADU?
Answer:
The proposed ADU is considered an addition for Title 24, Part 6. The existing 2x6 walls can be insulated with R-21 cavity insulation (§150.2[a]1Bvi) for prescriptive compliance. Continuous insulation is not required for these walls.
Example 9-5:
Question:
Can the ADU in the previous example get energy compliance credit using HERS verification of existing conditions for performance method compliance?
Answer:
No. Existing walls in newly conditioned spaces are not eligible for the HERS verification of existing conditions.
Example 9-6:
Question:
In the ADU in the previous example, is solar electricity generated by PV required for prescriptive or performance method compliance?
Answer:
No, PV is not required for Title 24 energy compliance for additions using any compliance approach.
Example 9-7:
Question:
The existing residence in the previous example has a ducted forced-air furnace enough heating capacity to heat the existing residence and the new ADU. Is this allowed for code compliance?
Answer:
No. The California Mechanical Code does not allow return air from an existing forced-air system to be discharged into another dwelling unit through the heating or cooling system. Therefore, the existing ducted furnace may not serve the existing home and the proposed ADU.
Example 9-7a:
Question:
When modeling a conversion of an existing garage to an accessory dwelling unit (ADU), and also making an addition to the existing house, can this be modeled together using the existing plus addition plus alteration approach?
Answer:
Yes. In this scenario, the existing home, addition, and ADU must be modeled as separate zones. Also, if the existing home has natural gas connected to it, the project must be modeled with natural gas being available.
Example 9-7b:
Question:
When converting an existing garage into an ADU in a high-rise residential building, do the high-rise residential Energy Code requirements apply to the ADU?
Answer:
Yes. The building occupancy type determines the compliance approach. If there are four or more habitable stories in the building, the ADU must comply with high-rise residential Energy Code requirements.
Example 9-7c:
Question:
When converting existing conditioned space, like a conditioned basement, into an ADU or junior ADU, is this an addition?
Answer:
No. This is an alteration. Energy Code requirements may be triggered if altering a component which is covered by the Energy Code. Some examples of alterations that are covered by the Energy Code are newly installed water heaters or mini-split HVAC systems, lighting upgrades, changes to the building envelope, etc.