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Single Family Energy Savings and Process Improvements for Additions and Alterations

Measure Description

Roof Replacements, Cool Roofs, and Insulation

Cool Roofs at Roof Replacement

This submeasure expands the current cool roof requirements at time of roof replacement for steep-slope and low-slope roofs to additional climate zones and revises the existing exceptions.

Currently, a variety of exceptions are allowed for steep-slope roofs on low-rise residential buildings. This proposed change revises the existing exceptions and allows for the following alternative options.

  1. Buildings with at least R-38ceiling or roof insulation
  2. Buildings with a radiant barrier in the attic where the radiant barrier is not installed directly over spaced sheathing
  3. Buildings with R-2 or greater insulation above the roof deck
  4. Buildings that have no ducts in the attic in Climate Zones 2, 4, 9,10, 12, and 14

These four alternatives are estimated to result in similar or greater total savings than a roof with an aged solar reflectance of 0.20. The existing radiant barrier option is revised to not allow this alternative path if a radiant barrier is installed over spaced sheathing, which reduces the impact of the radiant barrier by almost half. The existing option for ducts located outside of the attic is revised to only allow this option in climate zones where the cool roof is not cost effective based on a building with ducts inside conditioned space.

Roof Insulation at Low-Slope Roof Replacement

This submeasure adds a prescriptive requirement for above deck roof insulation at time of roof replacement for low-slope roofs. Currently, there is no requirement for low-rise residential buildings; there is an existing requirement for R-14 insulation for high-rise residential buildings.

The first exception allows for projects that already have continuous insulation installed at a value of R-10, about 70 percent of the R-value of the R-14 requirement. Modeling showed that adding additional insulation when the base condition already has some minimum level of continuous insulation is not always cost effective. The last three exceptions have been developed based on the current exceptions for the insulation requirement for high-rise residential and nonresidential buildings in Section141.0(b)2Biii; however, they have been revised to better low-rise residential roof reflect conditions. Item iii and iv allow for a lower level of continuous insulation thickness when certain conditions are met. Item iii qualifies this as R-4, which can be achieved with 1-inch or less of insulation.

  1. Existing roofs with a minimum continuous insulation R-value of at least R-10 are not required to meet the R-value requirements.
  2. Existing roofs with a minimum cavity insulation R-value of at least R-19 in certain climate zones. This exception is based on cost effectiveness results using the existing building prototypes with R-19 roof insulation,
  3. Continuous insulation may be reduced to R-4 where:
    1. Mechanical equipment is located on the roof and adding insulation would reduce the base flashing height to less than that allowable by the California Residential Code.
    2. The roof has sidewall or parapet walls and adding insulation would reduce the base flashing height to less than that allowed by the California Residential Code.
  4. Where adding insulation would result in the necessity to move existing exterior windows or doors, increased thickness may be reduced.
  5. Allowance to use tapered insulation provided that the average thermal resistance equals or exceeds the required value.

Electric Equipment Replacements

Electric Space Heating Equipment

Currently, Section 150.2(b)1G of Title 24, Part 6 limits prescriptive replacement heating equipment to natural gas, liquefied petroleum gas, the existing fuel type, or a heat pump. This language allows for new electric resistance heating equipment when the existing equipment is electric. The code change proposal prescriptively prohibits electric resistance replacement space heating equipment based on certain existing and upgrade conditions. Specifically, it’s prohibited when the replacement heating system is part of a new or replacement ducted cooling system. This existing condition represents a straightforward and cost-effective upgrade to a heat pump because the air conditioning and electrical infrastructure is already in place. The proposal does not cover non-ducted electric resistance heating systems or systems without central air conditioning, although these scenarios may be considered in future code cycles. Single family buildings in Climate Zones 7 and 15 and multifamily buildings in Climate Zones 6 through 8 and 15 are exempt from the proposed code change because low heating loads did not justify the incremental cost of the heat pump.

Electric Water Heating Equipment

Currently, Section 150.2(b)1Hiiid of Title 24, Part 6 limits prescriptive replacement water heating equipment to natural gas, propane, heat pump water heaters (in most climate zones under certain conditions) or a consumer electric water heater where no natural gas is connected to the existing water heater location. This language allows for electric resistance water heaters when no natural gas is connected to the existing water heater location. The code change proposal prohibits electric resistance replacement water heating equipment in most cases. Exceptions include when the existing electric2022Title 24, Part 6Draft CASE Report–2022-SF-EAA-D|96resistance water heater is located within conditioned space, whichadds complications that are further discussed in Section 3.2.2, or in spaces such as closets that are not large enough to accommodate a heat pump water heater. Electric resistance replacement water heaters in other locations would still be allowed if they are combined with a solar water heating system. Multifamily buildings with water heaters located outdoors or in exterior closets are exempt as a result of the cost effectiveness analysis.

Duct Measures

Prescriptive Duct Sealing

The proposed submeasure would reduce the total duct leakage requirement for single family buildings to less than or equal to 10 percent of system air handler airflow and the duct leakage to outside requirement to less than or equal to 7 percent of system air handler airflow. Additionally, the proposal revises the procedure for calculating duct leakage percentage to require that measured airflow be used in place of nominal airflow if measured airflow is available.There is no proposed reduction for leakage in low-rise multifamily buildings provided that the current requirement for new duct systems is 12 percent of system air handler air flow, versus 5 percent for single family buildings. The proposed revision to the procedure in Reference Appendix would impact both single family and multifamily buildings.

Prescriptive Duct Insulation

The proposed submeasure aligns the prescriptive duct insulation requirements with new construction Tables 150.1-A and 150.1-B for duct insulation, Option B and increase the required duct insulation from R-6 to R-8 in Climate Zones 1, 2, 4, 8 through 10, 12, and 13.

40 Foot Duct Extension Trigger

For low-rise residential buildings, the prescriptive duct sealing and duct insulation requirements of Section 150.2(b)1Dof the 2019 Title 24, Part 6 code are triggered when more than 40 feet of new or replacement space-conditioning system ducts are installed. When prescriptive requirements are not triggered, mandatory measures apply which per 150.0(m)1B require R-6 on all ducts in unconditioned space. The proposed submeasure would reduce the 40 foot threshold to 25 feet for systems serving existing spaces, and eliminate the threshold when ducts are extended to serve an addition applying the prescriptive requirements to any new ducts in an addition. In these cases, this submeasure would require duct sealing in all climate zones, where it is currently not required, and increase required duct insulation for ducts in unconditioned space from R-6 to R-8in climate zones where R-8 is prescriptively required

Attic Insulation

Attic Insulation for Alterations

This submeasure adds a prescriptive requirement for ceiling insulation and air sealing for altered ceilings below a vented attic. Currently, the only requirement for an altered ceiling for low-rise buildings is that the mandatory requirements for R-19 ceiling insulation in Section 150.0 be met. This submeasure proposes to add a prescriptive requirement that increases the insulation value to R-49 and requires air sealing components. All accessible areas of the ceiling plane between the attic and the conditioned space shall be sealed in accordance with Section 110.7of the standards.Recessed downlight luminaires in the ceiling must be covered with insulation to the same depth as the rest of the attic. This requires that fixtures that are not rated for Insulation Contact (IC) be retrofit or a fire rated cover be installed over the attic side of the fixture. If attic ventilation does not already comply with CBC requirements, ventilation must be added to meet code minimums.

This code change further clarifies that when an entirely new or complete replacement duct system is installed in a vented attic space, this constitutes an altered ceiling and the proposed attic insulation and air sealing requirements apply.

The proposed submeasure includes several additional exceptions, listed below.

  • Buildings with at least R-38 existing attic insulation
  • Buildings with asbestos or knob and tube wiring located in the attic.
  • Attics with limited vertical height that do not allow the installation of the required insulation R-value may install a lower R-value that maximizes the depth while still meeting code requirements including required air gaps
Attic Insulation for Additions

This submeasure increases the prescriptive insulation requirement for attics in additions less than or equal to 700 square feet.

ACM Reference Manual Compliance Options

Revised Blower Door/Air Infiltration Compliance Credit

As part of this submeasure the Statewide CASE Team is recommending a change to the default Standard Design air infiltration rate assumption for existing buildings as well as a change to how reduced infiltration is credited for single family alterations. Currently reduction in air infiltration is not credited in a performance run unless the post-retrofit blower door test reading is 5 ACH50 or less. This compliance credit allows credit for the full reduction in infiltration based on the test results when pre-and post-retrofit blower door testing is conducted by a HERS Rater. The Standard Design air infiltration rate default assumption for existing buildings is 5 ACH50; it’s recommended this be increased to 10 ACH50 to better represent the existing residential building stock.

Fireplace Removal Compliance Credit

This submeasure adds a compliance credit for removal of an existing wood burning fireplace. The credit can be taken if certain prescriptive requirements are met. Credit is awarded based on afixed infiltration reduction in the CBECC-Res software.

Quality Insulation Installation (QII) for Alterations Compliance Credit

This submeasure adds a QII compliance credit for altered wall, ceiling and floor assemblies. The credit can be taken for any altered assembly and does not need to apply to an entire building. It is similar to that allowed for new construction and additions, with some key differences due to challenges with existing buildings. Specifically, the following aspects of QII for new construction are proposed to not apply to the QII for alterations credit.

  • Subfloor sealed to create continuous airtight air barrier
  • Bottom plates sealed to the floor
  • Rim joist gaps and opening fully sealed
  • Inaccessible penetrations at the top plate in attics
  • Insulation around structural framing such as structural bracing, tie-downs, and framing of steel
  • Insulation in hard to access wall stud cavities
  • Insulated window and door headers

Provided that some of the criteria is relaxed, the proposed credit in the software is lower for altered assemblies than for new construction. For new construction assemblies without QII, the effective R-value of cavity insulation is reduced according to Table 3 of the 2019 Residential ACM, and ceilings below attic are modeled with added winter heat flow between the conditioned zone and attic to represent construction cavities open to the attic. When QII credit is taken in new construction, the effective R-value of cavity insulation is not derated and the additional heat flow from the conditioned zone to the attic is removed. Assuming that QII for altered assemblies would achieve most of the benefit of the cavity R-value and air sealing, the proposed QII credit for altered assemblies would have a reduced derate factor of 20 percent of the values shown in Table 3 of the2019 Residential ACM. For example, the cavity R-value of a wall without QII is derated to 70 percent of the rated R-value of the cavity insulation. An altered wall assembly taking the new QII credit would be derated to 94 percent of the rated R-value.

Relevant Documents

Measure proposals, supporting documents, and other outside references will be made public as they become available.

CASE Reports

Round Two Utility-Sponsored Stakeholder Meeting Materials

Round One Utility-Sponsored Stakeholder Meeting Materials

Provide Feedback

Draft CASE Report Now Available (Comments accepted until June 12, 2020)

This measure description will be updated as research is developed to support the 2022 code cycle. For questions or suggestions, email Include the measure name in the subject line.


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The Statewide CASE Team values input from all stakeholders engaged in the Title 24, Part 6 code change process. We encourage the open exchange of code change comments and concerns.

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