Addition and alteration compliance is based on Energy Code, Section 150.2. The energy budget for additions and alterations is based on TDV energy. Alterations must model the entire dwelling unit. Additions may be modeled as addition alone, as “existing+addition+alteration,” or the entire building may be modeled as an entirely new building (whole building, Section 150.2(c)).
Additions that are 1,000 ft2 or less are exempt from dwelling unit ventilation requirements of Section 150.0(o)1C, Section 150.0(o)1E, or Section 150.0(o)1F. When an addition to any building creates a new dwelling unit, this exception does not apply.
The standard design does not include:
- Cool roof when an addition is 300 ft2 or less.
- Ventilation cooling for additions that are 1,000 ft2 or less.
- Solar generation/PV requirements.
When an accessory dwelling unit (ADU) is detached and newly constructed, it must comply using the whole building approach as described in Section 2.10.2 Whole Building. When an ADU is created by conditioning an existing unconditioned space and is either attached or detached, it may comply using any of the compliance approaches allowed for additions as described in Section 2.10.3 Alteration-Alone Approach or Section 2.10.4 Addition-Alone Approach.
The entire proposed building, including all additions or alterations or both, is modeled the same as a newly constructed building. The building complies if the proposed design uses equal to or less energy than the standard design.
The proposed alteration alone floor area is modeled. The alteration requirements of Section 150.2(b) are applied to any features that do not exist.
The proposed addition alone is modeled the same as a newly constructed building except that the internal gains are prorated based on the size of the dwelling. None of the exceptions included for prescriptive additions, which are implemented in the existing plus addition plus alteration compliance approach (Section 2.10.5 Existing + Addition + Alteration Approach), are given to the addition alone approach. (See Energy Code, Section 150.2(a)2B The addition complies if the proposed design uses equal to or less space heating, space cooling, and water heating TDV energy than the standard design.
The addition-alone approach shall not be used when alterations to the existing building are proposed. Modifications to any surfaces between the existing building and the addition are part of the addition and are not considered alterations.
Proposed Design
The user shall indicate that an addition alone is being modeled and enter the conditioned floor area of the addition. Any surfaces that are between the existing building and the addition are not modeled or are treated as adiabatic surfaces. All other features of the addition shall be modeled the same as a newly constructed building.
When an existing HVAC system is extended to serve the addition, the standard design shall assume the same efficiency for the HVAC equipment as the proposed design. (See Section 2.4.1 Heating Subsystems and Section 2.4.6 Cooling Subsystems.)
When a dual-glazed greenhouse or garden window is installed in an addition or alteration, the proposed design U-factor can be assumed to be 0.30.
Standard Design
The addition alone is modeled the same as a newly constructed building, with the following exceptions:
- When roofing requirements are included in Table 150.1-A, they are included in the standard design if the added conditioned floor area is greater than 300 ft2.
- When ventilation cooling (whole-house fan) is required by Table 150.1-A, it is included in the standard design when the added conditioned floor area is greater than 1,000 ft2. The capacity shall be based on 1.5 CFM/ft2 of conditioned floor area for the entire dwelling unit conditioned floor area.
- When compliance with IAQ requirements of Section 150.0(o) apply to an addition with greater than 1,000 ft2 added, the conditioned floor area of the entire dwelling unit shall be used to determine the required ventilation airflow. For additions with 1,000 ft2 or less of added conditioned floor area, no IAQ requirements apply.
- PV requirements are not included.
- The standard design HVAC system is a natural gas furnace (or propane if natural gas is not available) if the proposed design has a gas heating system. The standard design HVAC system is a split heat pump if the proposed design has an electric heating system. See Section 2.4.1 Heating Subsystems for equipment efficiencies and operating details for each type of system. The cooling system for the standard design building is a nonzonal control system, split-system ducted cooling system, meeting the minimum requirements of the Appliance Efficiency Regulations. See Section 2.4.6 Cooling Subsystems for equipment efficiencies and operating details for each type of system.
- The domestic water heating system is a natural gas tankless (or propane if natural gas is not available) if the proposed design has a gas water heating system. The standard design water heating system is a heat pump water heater if the proposed design has an electric water heating system. For additions 500 square feet or less, the standard design is an instantaneous electric water heater if the proposed design is an instantaneous electric water heater, or the standard design is an electric consumer storage water heater less than or equal to 20 gallons if the proposed design is an electric consumer storage water heater less than or equal to 20 gallons.
Energy Code Section 150.2(a)2 contains the provisions for additions and Section 150.2(b)2 for alterations when the existing building is included in the calculations. These provisions are the “Existing + Addition + Alteration” (or “E+A+A”) performance approach.
Proposed Design
The proposed design is modeled by identifying each energy feature as part of the existing building (as existing, altered, or new), or as part of the addition. The compliance software uses this information to create an E+A+A standard design using the rules in the standards that take into account whether altered components meet or exceed the threshold at which they receive a compliance credit and whether any related measures are triggered by altering a given component.
For building surfaces and systems designated below, all compliance software must provide an input field with labels for the proposed design, which define how the standard design requirements are established based on the option selected by the software user:
- Existing: The surface or system remains unchanged within the proposed design. (Both standard design and proposed design have the same features and characteristics.)
- Altered: the surface or system is altered in the proposed design. No verification of existing conditions is assumed with this designation.
- Verified Altered: the surface or system is altered in the proposed design, and the original condition is verified by a HERS Rater (an optional selection).
- New: a new surface or system is added in the proposed design (may be in the existing building or the addition).
Deleted features are not included in the proposed design.
Section 150.2, Table 150.2-D specifies the details of the standard design for altered components based on whether verification of existing conditions is selected or not:
- Altered with no third-party verification of existing conditions (the default selection). This compliance path does not require an on-site inspection of existing conditions prior to the start of construction. The attributes of the existing condition are undefined, with the standard design for altered components based on Section 150.2, Table 150.2-D , and the climate zone. Energy compliance credit or penalty is a function of the difference between the value for that specific feature allowed in Table 150.2-D and the modeled/installed efficiency of the feature.
- Verified Altered existing conditions. This compliance path requires that a HERS Rater perform an on-site inspection of pre-alteration conditions prior to construction. If an altered component or system meets or exceeds the prescriptive alteration requirements, the compliance software uses the user-defined and verified existing condition as the standard design value. Energy compliance credit is then based on the difference between the verified existing condition for that altered feature and the modeled/installed efficiency of the proposed design.
Standard Design
The standard design includes QII for additions greater than 700 ft2 in any low-rise single-family residential building in Climate Zones 1-16 (Section 150.2(a)1Bv).
The provisions of Section 150.2(a)1Aiv, as applied to converting an existing unconditioned space to conditioned space, are accommodations made by the HERS Rater in the field. No adjustments to the energy budget are made.
Standard Design
The standard design does not include PV for additions and alterations.
Standard Design
The standard design roof/ceiling construction assembly is based on the proposed design assembly type as shown in Table 27. For additions equal to or less than 700 ft2, radiant barrier requirements follow Option C (Section 150.1(c)9B). The standard design for unaltered ceilings and roofs is the existing condition.
Proposed Design Roof/Ceiling Types | Addition ≤300ft2 | Addition >300ft2 and ≤700 ft | Addition >700ft2 | Altered | Verified Altered |
Roof Deck Insulation (below - deck, where required) at vented attic | NR | NR | CZ 4, 8-16 = R-19 | CZ 3, 5-7 = NR CZ 1, 2, 4, 8-16 = R-14/U-0.039 | Existing |
Ceilings Below Attic | CZ 1, 2, 4, 8 -16 = R-38 CZ 3, 5-7 = R-30 | CZ 1, 2, 4, 8-16 = R-38 CZ 3, 5-7 = R-30 | CZ 1, 2, 4, 8-16 = R-38 CZ 3, 5-7 = R-30 | CZ 5, 7 = R-19 CZ 1-4, 6, 8-16 = R-49 | Existing |
Non-Attic (Cathedral) Ceilings and Roofs | R-22 / U-0.043 | R-22 / U-0.043 | Same as above | R-19 / U-0.054 | Existing |
Radiant Barrier | CZ 2-15 REQ CZ 1, 16 NR | CZ 2-15 REQ CZ 1, 16 NR | CZ 2, 3, 5-7 REQ CZ 1, 4, 8-16 NR | NR | Existing |
Roofing Surface (Cool Roof) Steep-Sloped | NR | CZ 10-15 = 0.20 Reflectance, = 0.75 Emittance | CZ 10-15 = 0.20 Reflectance, = 0.75 Emittance | CZ 4, 8 -15 = 0.20 Reflectance = 0.75 Emittance | Existing |
Roofing Surface (Cool Roof) Low-Sloped | NR | CZ 13, 15 = 0.63 Reflectance, = 0.75 Emittance | CZ 13, 15 = 0.63 Reflectance, = 0.75 Emittance | CZ 4, 6- 15 = 0.63 Reflectance = 0.75 Emittance | Existing |
Above Deck Insulation, Low-Sloped | NR | NR | NR | CZ 1, 2, 4, 8-16 R-14 continuous | Existing |
Source: California Energy Commission
Proposed Design
Existing structures with insulated wood-framed walls that are being converted to conditioned space using an E+A+A approach are allowed to show compliance using the existing wall framing, without having to upgrade to current prescriptive continuous insulation requirements. The walls are modeled as an assembly with the existing framing and either R-15 (in 2x4 framing) or R-21 (in 2x6 framing) insulation (Exception to Section 150.0(c)1 and Section 150.2(a)1).
Standard Design
The areas, orientation, and tilt of existing, new, and altered net exterior wall areas (with windows and doors subtracted) are the same in the existing and addition portions of standard design as in the proposed design.
If the proposed wall area is framed, the gross exterior wall area (excluding knee walls) is equally divided among the four building orientations: front, left, back and right. The gross exterior wall area of any unframed walls is also equally divided among the four orientations in the standard design.
The standard design exterior wall construction assembly is based on the proposed design assembly type as shown in Table 28. Framed walls are modeled as 16-in. on center wood framing. The standard design for unaltered walls is the existing condition.
The standard design for exterior opaque or swinging doors is 0.20 U-factor. Fire-rated doors (from the house to garage) use the proposed design door U-factor as the standard design U-factor.
Proposed Design Exterior Wall Assembly Type or Door | Addition | Altered | Verified Altered |
Framed & Non-Mass Exterior Walls | CZ 1-5, 8-16 = R-21 + R-5 in 2x6 (U0.048) CZ 6-7 = R-15 + R-4 in 2x4 (U-0.065) | R-13 in 2x4 R-20 in 2x6 | Existing |
Wood framed existing walls where siding is not removed , or an e xtension of an existing wall | R-15 in 2x 4 R-21 in 2x6 | R-13 in 2x4 R-20 in 2x6 | Existing |
Framed Wall Adjacent to Unconditioned (e.g., Demising or Garage Wall) | R-15 in 2x 4 R-21 in 2x6 | R-13 in 2x4 R-20 in 2x6 | Existing |
Above Grade Mass Interior Insulated | CZ 1-15 = R-13 (0.077) CZ 16 = R-17 (0.059) | N/R Mandatory requirements have no insulation for mass walls | Existing |
Below Grade Mass Interior Insulation | CZ 1-15 = R-13 (0.077) CZ 16 = R-15 (0.067) | N/R Mandatory requirements have no insulation for mass walls | Existing |
Swinging Doors | 0.20 | 0.20 | Existing |
Source: California Energy Commission
Proposed Design
Fenestration areas are modeled in the addition as new. In an existing building, they may be existing, altered, or new. Altered (replacement) fenestration is defined in Section 150.2(b)1B as “existing fenestration area in an existing wall or roof [which is] replaced with a new manufactured fenestration product ... Up to the total fenestration area removed in the existing wall or roof ...“ Altered also includes fenestration installed in the same existing wall, even if in a different location on that wall. Added fenestration area in an existing wall or roof is fenestration that did not previously exist and is modeled as new.
Standard Design
Standard design fenestration U-factor and SHGC are based on the scope of the project (addition vs. alteration), and for additions the square footage is taken into consideration as well, as shown in Table 29. Vertical glazing includes all fenestration in exterior walls such as windows, clerestories, and glazed doors. Skylights include all glazed openings in roofs and ceilings.
New fenestration in an alteration is modeled with the same U-factor and SHGC as required for an addition.
West-facing limitations are combined with the maximum fenestration allowed and are not an additional allowance.
The standard design is set for fenestration areas and orientations as shown in Table 29:
- Proposed design < allowed percentage of total fenestration area:
In the existing building, the standard design uses the same area and orientation of each existing or altered fenestration area (in the respective existing or altered wall or roof.)
In the addition, new fenestration is divided equally among the four project compass points similar to new gross wall areas in the addition described above.
- Proposed design > allowed percentage of total fenestration area:
The standard design first calculates the allowed total fenestration area as the total existing and altered fenestration area in existing or altered walls and roofs. Added to this is the percentage of fenestration allowed in the addition, based on the conditioned floor area of the addition.
Proposed Design Fenestration Type | Addition ≤ 400 ft2 | Addition > 400 and ≤ 700 ft2 | Addition > 700 ft2 | Altered | Verified Altered | |
Vertical Glazing: Area and Orientation | 75 ft2 or 30% | 120 ft2 or 25% | 175 ft2 or 20% | See full description below. | Existing | |
West Facing Maximum Allowed | CZ 2, 4, 6 -15=60 ft2 | CZ 2, 4, 6 -15=60 ft2 | CZ 2, 4, 6 -15=70 ft2 or 5% | NR | NR | |
Vertical Glazing: U-Factor | 0.30 | 0.30 | 0.30 | 0.40 | See below | |
Vertical Glazing: SHGC | CZ 2, 4, 6-15=0.23 CZ 1,3, 5 & 16=0.35 | CZ 2, 4, 6-15=0.23 CZ 1,3, 5 & 16=0.35 | CZ 2, 4, 6-15=0.23 CZ 1,3, 5 & 16=0.35 | CZ 2, 4, 6-15=0.35 CZ 1,3, 5 & 16=0.35 | Existing | |
Skylight: Area and Orientation | No skylight area in the standard design | No skylight area in the standard design | No skylight area in the standard design | NR | Existing | |
Skylight: U-Factor | 0.30 | 0.30 | 0.30 | 0.55 | Existing | |
Skylight: SHGC | CZ 2, 4, 6 -15=0.23 CZ 1,3 5 & 16 =0.35 | CZ 2, 4, 6 -15=0.23 CZ 1,3 5 & 16 =0.35 | CZ 2, 4, 6 -15=0.23 CZ 1,3 5 & 16 =0.35 | CZ 2, 4, 6 -15=0.30 CZ 1,3 5 & 16 =0.35 | Existing | |
Source: California Energy Commission
Standard Design
The standard design for a proposed building with overhangs, sidefins, and exterior shades is shown in Table 30. Exterior shading (limited to bug screens) is treated differently than fixed overhangs and sidefins, as explained in Section 2.5.6.9 Exterior Shading.
Proposed Design Shading Type | Addition | Altered | Verified Altered |
Overhangs and Sidefins | No overhangs or sidefins | Proposed altered condition | Same as altered |
Exterior Shading | Standard (bug screens on fenestration, none on skylights) | Proposed altered condition | Existing exterior shading |
Window Film | No window film | Proposed altered condition | Existing exterior shading |
Source: California Energy Commission
Proposed Design
A window film must have at least a 15-year warranty and is treated as a window replacement. The values modeled are either the default values from Tables 110.6-A and 110.6-B or the NFRC Window Film Energy Performance Label.
Standard Design
Table 150.2-C requires that the standard design be based on the mandatory requirements from Section 150.0(d). The standard design for floors is shown in Table 31.
Proposed Design Floor Type | Addition | Altered (mandatory) | Verified Altered |
Raised Floor Over Crawl Space or Over Exterior | R-19 in 2x6 16” o.c. wood framing | R-19 in 2x6 16” o.c. wood framing | If proposed U < 0.037, standard design = existing raised; if proposed U > 0.037, standard design = 0.037 |
Slab-on-Grade: Unheated | CZ1-15: R-0 CZ16: R-7 16” vertical | R-0 | Existing unheated slab-on-grade |
Slab-on-Grade: Heated | CZ1-15: R-5 16” vertical CZ 16: R-10 16” vertical | CZ1-15: R-5 16” vertical CZ 16: R-10 16” vertical | Existing heated slab-on-grade |
Raised Concrete Slab | CZ1,2,11,13,14,16: R-8 CZ3-10: R-0 CZ12,15: R-4 | R-0 | Existing raised concrete slab |
Source: California Energy Commission
Standard Design
The standard design for thermal mass in existing plus addition plus alteration calculations is the same as for all newly constructed buildings as explained in Section 2.5.4.1 Internal Thermal Mass.
Standard Design
Standard design air leakage and infiltration are shown in Table 32.
Proposed Air Leakage and Infiltration | Addition | Altered | Verified Altered |
Single-Family Residential Buildings | 5 ACH50 | 5 ACH50 | Diagnostic testing of existing ACH50 value by HERS Rater |
Source: California Energy Commission
Standard Design
The standard design for space-conditioning systems is shown in Table 33.
When cooling ventilation (whole-house fan) is required by Section 150.1 and Section 150.2, the capacity is 1.5 CFM/ft2 of conditioned floor area for the entire dwelling unit.
When compliance with IAQ requirements of Section 150.0(o) apply to an addition with greater than 1,000 ft2 added, the conditioned floor area of the entire dwelling unit is used to determine the required ventilation airflow. For additions with 1,000 ft2 or less of added conditioned floor area, no IAQ requirements shall apply.
Proposed Design Space-Conditioning System Type | Addition | Altered | Verified Altered |
Heating System Efficiency | See Section 2.10.4 Addition-Alone Approach and 2015 Federal Appliance Standards based on fuel source and equipment type | Existing heating fuel type and equipment type/efficiency. If the existing equipment is electric resistance and none of the exceptions to Section150.2(b)1G are met, the Standard Design system shall be a heat pump meeting the requirements of Section 2.10.4 Addition-Alone Approach. | Same as altered. |
Cooling System Efficiency | See Section 2.10.4 Addition-Alone Approach and 2015 Federal Appliance Standards based on fuel source and equipment type | Same as Addition | Existing cooling equipment type/efficiency |
Refrigerant Charge | CZ 2, 8-15: Yes CZ 1, 3-7: No | Same as Addition | Existing |
Whole-House Fan (WHF) applies only if addition > 1,000 ft2 | CZ 8-14; 1.5 CFM/ft2 | N/A | Existing condition. To count as Existing the WHF must be > 1.5 CFM/ft2 and be CEC-rated |
Indoor Air Quality applies only if addition > 1,000 ft2 or if addition is a dwelling unit | Meet mandatory ventilation for entire dwelling | Same as Addition | Existing |
Source: California Energy Commission
Proposed Design
Duct insulation shall be based on the new or replacement R-value input by the user. Duct leakage shall be based on the tested duct leakage rate entered by the user or a default rate of 30 percent.
Standard Design
Proposed Design Duct System Type | No Verification of Existing Conditions | Verified Existing Conditions |
Altered or Extended Ducts >25 ft | CZ 1-2 , 4, 8-16 : Duct insulation R- 8 and total leakage of 10% CZ 3, 5-7 : Duct insulation R- 6 and total leakage of 10% | Existing duct R-value and total leakage the lesser of 30% or the existing leakage rate |
New Ducts | CZ 1-2, 4, 8-16: Duct insulation R-8 and total leakage of 7% CZ 3, 5-7: Duct insulation R-6 and total leakage of 7% | N/A |
Based on Table 150.2-A
Note 1: Refer to Section 150.2(b)1Diia for definition of an “Entirely New or Complete Replacement Duct System."
Source: California Energy Commission
Standard Design
Proposed Design Water Heating System Type | Addition (adding water heater) | Altered | Verified Altered |
Single-Family Residential Buildings | Prescriptive water heating system per Section 2.10.4 Addition-Alone Approach | Proposed fuel type, proposed tank type, mandatory requirements with no solar | Existing water heater type(s), efficiency, distribution system. |
Source: California Energy Commission