9.3 Compliance Approaches

Apart from meeting all applicable mandatory requirements (Section 9.4), additions and alterations must demonstrate compliance using a prescriptive or performance method.

There are several compliance paths depending on the scope of work:

1.  Addition only, where no changes are made to the existing building except removal of roofs, exterior walls/fenestration, and floors required as a result of the addition.

2.  Alterations only, where there is no addition (that is, no increase in conditioned floor area and volume or adding conditioning to a previously unconditioned space).

3.  Addition and alterations, where there are both additions and alterations to the existing building.

For each of these permit scenarios, Table 9-1 summarizes the available compliance approaches for low-rise residential additions and alterations.

Table 9-1: Compliance Alternatives for Residential Additions and Alterations

9.3.1    Additions

Regardless of compliance approach selected, the following exceptions apply:

1.  Additions of ≤ 300 ft² do not require a cool roof product (if required by §150.1(c)11) to be installed.

2.  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).

3.  Existing space conditioning systems that are extended to provide conditioning to an addition are not required to meet the Energy Standards (§150.2(a) Exception 4).

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.

5.  Photovoltaic (PV) requirements do not apply to additions/alterations.

A.   Addition Alone

In this compliance scenario, the addition alone is modeled using the compliance software, and the existing building is not modeled. This approach may work well when the existing building is not undergoing alterations, and the permitted work scope covers only the addition.

1.  Advantages: Very little information about the existing building is needed (existing conditioned floor area and number of bedrooms). The existing building is not modeled.

2.  Disadvantages: Many prescriptive allowances for additions do not apply to the addition alone performance approach. For example, a 400 ft² addition is allowed a 30 percent fenestration area limit if complying using existing + addition, while only 20 percent is allowed when complying as an addition alone. Alterations to the existing conditions that improve the energy performance of the existing building cannot be used in this approach as “trade-offs” with the addition.

B.   Existing + Addition + Alteration

In this compliance scenario, the entire building is included in the analysis. This approach does not require unaltered components to be brought into compliance.

1.  Advantages: This approach offers the most flexibility by modeling improvements to the existing building. The energy budgets include the more generous glazing allowances given to prescriptive compliance. Note: There is no requirement to make alterations to the existing building using this approach.

2.  Disadvantages: Plans and data for the existing building are needed, increasing the time and complexity of the calculations.

C.   Existing + Addition as New Construction

Demonstrating compliance as a whole new building, which entails combining existing plus the addition as all new construction, is another approach. This approach is used when the changes are extensive. Compliance can be difficult because all existing features must be brought up to the current code.

9.3.2    Additions and Alterations Combined

9.3.2.1    Prescriptive

When a low-rise residential project includes an addition and alterations, the prescriptive requirements for each condition must be met. The addition may comply with the appropriate prescriptive addition approach and documented with the applicable form (for example, CF1R-ADD-01).

The alterations must also meet all prescriptive requirements and be documented with the specific compliance documentation for alterations (for example, CF1R-ALT-02).

9.3.2.2    Performance

The performance approach that includes both additions and may include alterations is called “Existing + Addition + Alterations.” (See Section 9.5.2.) There are two ways to analyze the building using this method: compliance with third-party verification of all existing conditions altered or compliance without third-party verification.

9.3.3    Alterations Only

9.3.3.1    Prescriptive

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 are specific to the building site climate zone. There are also several exceptions based on either climate zone or other conditions.

It is important to note that every applicable prescriptive requirement must be met; otherwise, the building must comply using a performance approach. However, the energy budget is based on prescriptive requirements. So if one or more proposed alterations do not comply, the other alterations must exceed prescriptive requirements, or the project may not comply with the performance approach.

Under the prescriptive alteration approach, the appropriate certificate of compliance (for example, CF1R-ALT-02) form is completed and submitted for a permit. If any mandatory or prescriptive measures require HERS verification or testing (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 submittal to the enforcement agency.

9.3.3.2    Performance

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:

1.  Existing + Alterations: If multiple components or systems are being altered or if the proposed modification(s) exceed the prescriptive requirements, then the existing + alterations performance approach may be used to make trade-offs.

2.  Compliance Without Third-Party Verification: This option allows for compliance of the alterations without the need for third-party inspection to verify existing conditions being altered.

3.  Compliance With Third-Party Verification: This option allows for compliance of the alterations only with third-party inspection to verify existing conditions being altered.

4.  Existing + Alterations as new construction: This option is  the most difficult.

9.3.4    Wall Exceptions to Continuous Insulation

9.3.4.1    Wall Extension

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.

9.3.4.2    Existing Wall With Siding

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.

9.3.5    Accessory Dwelling Units (ADUs)

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.

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 treated as an addition or may be a new dwelling unit. See Figure 9-2 to determine the compliance requirements. Although the Energy Standards that apply 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 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 measures.

A.  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).

B.  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.

C.  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.

D. 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

1.   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 §150.0(o)1C. 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.

2.   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.