ADU Exemptions for Title 24 Energy Code (2016 Code)

What is an ADU?

Accessory dwelling units (ADUs) are most commonly defined as secondary dwelling units on residential lots. They can be used to house family (known also as granny or in-law units), visitors, or even as rental properties to supplement income. ADUs, like all other residential structures in California, are subject to the Energy Code.

How are ADUs treated under Title 24 Code?

ADUs can be treated in two different ways – as new construction, or as an addition.

The only scenario where an ADU would be considered a newly constructed building is if it was a new structure and shared no common walls with the existing building. ADUs that fall into this category do not qualify for any exemptions under the Energy Code.

Additions are changes to a building that increase conditioned floor area and conditioned volume. Attached ADUs, as well as converted existing structures, are considered additions.

Here are a couple of common scenarios that will help with classification:

• When an existing attached unconditioned structure (like a garage) is converted to an ADU, this is considered an addition. See Figure 1 below for an example.

Figure 1: Existing attached unconditioned structure converted to an ADU. This is treated as an addition.

• When an ADU is built new sharing a common wall with the existing house, this is considered an addition. See Figure 2 below for an example.

Figure 2: New attached ADU. This is treated as an addition.

• When an existing detached unconditioned structure (like a garage) is converted to an ADU, this is an addition. See Figure 3 below for an example.

Figure 3: Existing detached unconditioned structure converted to an ADU. This is treated as an addition.

• When an ADU is built new and is detached from the existing house, this is a newly constructed building. See Figure 4 below for an example.

Figure 4: New detached ADU. This is treated as new construction.

Exemptions for Unconditioned Structure Conversions to ADUs

When an existing attached or detached unconditioned structure (like those shown in Figures 1 or 3 above) is converted to an ADU the walls can be treated as “wall extensions” and can meet the insulation requirements based on their existing dimensions, as described in Section 150.2(a)1Ai and 150.2(a)1Bii of the 2016 Residential Compliance Manual.

Thus, the following insulation is required in this scenario:

• 2x4 Wall: R-15 Insulation

• 2x6 Wall: R-19 Insulation

This is a huge saving, as under normal circumstances, an addition or a newly constructed building would be held to the requirements in Table 150.1-A of the 2016 Residential Compliance Manual, which mandate much higher insulation values.

Take the following into consideration when reviewing Table 1 below, and compare the "typical construction" that is required with and without the ADU exemption.

Table 1: Comparison of exterior wood-framed wall requirements. Note the large difference in both U-Factor and typical construction as a result of using the ADU Exemption.

How will this exemption show up on my CF-1R?

If using a prescriptive approach, the exterior walls will show up just as a normal “R-15 Wall” or “R-19 Wall” with the comment “wall extension” in the far right-hand side of the table.

If using a performance approach, it becomes a bit more cumbersome:

• The prescriptive exterior wall U-factor required for the applicable climate zone will be identified by your energy analyst (e.g., U-0.051 in climate zones 1-5 and 8-16, or U-0.065 in climate zones 6-7).

• Your energy analyst should create a wall construction and name it “Prescriptive Wall” (so it is not confused for actual construction assemblies).

• This wall construction should be used for all of the ADU’s exterior walls. The construction details to achieve exactly these U-factors can be found in Joint Appendix 4.3 of the 2016 Residential Compliance Manual or at CBECC-RES FAQs (April 10 2018)

Figure 5 below shows an example of how this will look in your CF-1R.

Figure 5: Example CF-1R showing a Prescriptive Exterior Wall using the ADU Exemption.

This provision is allowed for all compliance approaches (existing + addition and addition alone), as well as non-ADU projects.

To help avoid plan check comments, a thorough energy analyst should be sure to document their modeling assumption in their notes section of the CF-1R. Figure 6 below is an example of this in a CF-1R.

Figure 6: Example CF-1R notes indicating use of the ADU Exemption.

During construction, only R-15 or R-19 cavity insulation is required.

Whole Building Ventilation Requirements for ADUs

For ADUs that are additions, the whole building ventilation requirements apply to additions that are greater than 1000 square feet.

While not required, it is recommended that the whole building ventilation requirements be met for new dwelling units. All other applicable ventilation requirements must be met. For example, if a bathroom or kitchen is part of the addition, the local exhaust requirements for those spaces must be met. Refer to Section 4.6.5 of the 2016 Residential Compliance Manual for more details.

C&S Energy Pro is committed to getting a fast turnaround on your Title 24 documents which will help ensure construction projects are completed on time and that consumers will be able to move into their homes quicker.  Avoid the hassle of long wait times generally associated with Title 24 documentation and call us today!

References

• California Energy Commission Blueprint Issue 122

• CBECC-RES Frequently Asked Questions (April 10, 2018)