11.3   Building Envelope Requirements

This chapter covers building envelope features and compliance strategies for newly constructed multifamily buildings and additions and alterations to multifamily buildings. It highlights the energy code requirements that affect the design of the building envelope. Multifamily envelope requirements, except for HERS requirements, apply to all dwelling units and common use areas in all multifamily buildings. HERS envelope requirements apply to multifamily buildings up to three habitable stories. Nonresidential occupancies in a mixed-use building must comply with nonresidential envelope requirements outlined in Chapter 3.

This chapter is organized by building envelope component and includes:

•    A description of opaque envelope requirements related to air sealing and leakage, insulation, roofing products, radiant barriers, air barriers, vapor retarders, and attic ventilation. The opaque envelope includes roof, wall, and floor assemblies.

•    A description of fenestration requirements for U-factor, solar heat gain coefficient (SHGC), visible transmittance (VT), and window area.

•    Verification requirements, including those for QII.

•    Additions and alterations requirements

Table 11-5 summarizes the location of mandatory, prescriptive, and performance requirements in the multifamily standards and in the compliance manual.

Table 11-5: Overview of Envelope Requirements in the Energy Code and
Compliance Manual Organization

Source: California Energy Commission

11.3.1      What’s New for the 2022 Energy Code

The 2022 Building Energy Efficiency Standards for multifamily buildings consolidate requirements for all multifamily building types, with requirements based on assembly or fenestration type rather than number of stories. This reclassification allows for better alignment of energy efficiency requirements with fire safety and structural requirements. Table 170.2-A of the Energy Code captures the updated requirements for all multifamily buildings. Notable 2022 envelope changes include:

•    Buildings up to three habitable stories have a new prescriptive insulation Option D for roof assemblies without attics.

•    Buildings with four stories or more with attics have new prescriptive Options B or C for roof and ceiling insulation.

•    Prescriptive roof reflectance and emissivity requirements depend on roof options Option B, C, or D

•    Prescriptive roof reflectance requirements increased to 0.63 in climate zones 9-11 and 13-15 for buildings with low-sloped roofs and no attic.

•    Mandatory and prescriptive wall U-factors are recategorized by assembly type and by fire rating for framed assemblies. This results in many climate zone-specific adjustments. The greatest changes include reduced U-factors for framed walls in multifamily buildings with four or more stories.

•    Prescriptive fenestration properties, including U-factor, solar heat gain coefficient (SHGC), and visual transmittance (VT), depend on categorization into curtainwall, Class AW, or all other fenestration, and vary by climate zone. There is no distinction between fixed and operable windows. The greatest change is for fenestration in multifamily buildings with four or more stories that fall into all other fenestration category (not curtainwall or Class AW).

•    Prescriptive requirements for fenestration properties in multifamily building additions and alterations depend on window classification (curtainwall, Class AW, or all other).

•    Prescriptive fenestration area is limited to both 40 percent window-to-wall ratio and 20 percent window-to-floor ratio.

11.3.2      Opaque Envelope

This section of the building envelope chapter addresses the requirements for air leakage, roof products, roof and ceiling insulation, radiant barriers, and vapor retarders.

11.3.2.1    General Insulation Requirements

§110.8(a) – (c), 110.8(g)

Insulation materials must be certified by the Department of Consumer Affairs, Bureau of Household Goods and Services and listed in the Directory of Certified Insulation Materials. Urea formaldehyde foam insulation, flame spread index and smoke development index must meet requirements for multifamily and nonresidential buildings.

11.3.2.2    Ceiling and Roof Insulation

11.3.2.3    Mandatory Requirements

A.    Attic Roof

Roof/ceiling construction assemblies with an attic space must have at least R-22 insulation between wood framing members or a maximum U-factor of 0.043. Some areas of the roof/ceiling can be greater than the maximum U-factor if other areas have lower U-factors such that the weighted average U-factor for the overall ceiling/roof is 0.043 or less. Metal framed assemblies must also have a weighted U-factor of 0.043 or less.

If insulation is not penetrated by framing, such as rigid insulation laid over a structural deck, then the rigid insulation can have a rated R-value of less than R-22 so long as the total roof/ceiling assembly U-factor is not greater than U-0.043.

Loose fill insulation must be blown in evenly and insulation levels must be documented on the certificate of installation. The insulation level can be verified by checking that the depth of insulation conforms to the manufacturer’s coverage chart for achieving the required R-value. The insulation also must meet the manufacturer’s specified minimum weight per square foot for the corresponding R-value.

B.    Non Attic Roof

For roof/ceiling construction assemblies without an attic space, the maximum weighted average U-factor is 0.098 for metal building and 0.075 for wood framing and others. If insulation is installed at the roof, vents or openings that penetrate the roof deck to the outdoor are prohibited.

Regardless of whether or not there is an attic space, insulation mustmust be installed in direct contact with the air barrier.

C.    Wet Insulation Systems

Wet insulation systems are covered in Section 3.2.4.1 for multifamily and nonresidential buildings.

D.    Recessed Luminaires

Luminaires recessed in insulated ceilings can create thermal bridging through the assembly. Not only does this degrade the performance of the ceiling assembly, but it can permit condensation on a cold surface of the luminaire if exposed to moist air, as in a bathroom.

Figure 11-1. IC-Rated Luminaire (Light Fixture)

Luminaires recessed in insulated ceilings must meet three requirements.

1.    They must be listed as defined in the Article 100 of the California Electric Code for zero clearance insulation contact (IC) by Underwriters Laboratories or other testing/rating laboratories recognized by the International Code Council (ICC). This enables insulation to be in direct contact with the luminaire.

2.    The luminaire must have a label certified as per §160.5(a) for airtight (AT) construction. Airtight construction means that leakage through the luminaire will not exceed 2.0 CFM when exposed to a 75 Pa pressure difference, when tested in accordance with ASTM E283.

3.    The luminaire must be sealed with a gasket or caulk between the housing and ceiling.

11.3.3      Prescriptive Requirements

The Energy Code is designed to offer flexibility to builders and designers of multifamily newly constructed buildings in terms of achieving the intended energy efficiency targets. Thus, the Energy Code offers several compliance options for roof insulation in multifamily buildings, as shown in Table 11-6.

Table 11-6: Summary of Multifamily Roof Insulation Options

Source: California Energy Commission

Option B has a vented attic space and uses a combination of ceiling insulation and below roof deck insulation.

Option C also has a vented attic space but uses ceiling insulation only.

Option D has no attic space and uses U-factor requirements instead of insulation levels.

The prescriptive requirements for Option B and Option C assume that the building is built with the following construction practices:

1.    The attic is ventilated with an appropriate free vent area as described below.

2.    The roof is constructed with standard wood rafters and trusses.

3.    For Option B, the outermost layer of the roof construction is either tiles or a roofing product installed with an air gap between it and the roof deck.

4.    The air handler and ducts are in the ventilated attic for Option B and are otherwise in conditioned space for Option C.

5.    The air barrier is located at the ceiling (except cathedral and sealed attic roof/ceiling systems).

If a building design does not meet all of these specifications, for example an unvented attic, it must comply through the performance approach as described in Section 11.1.9.10.

Section 170.2 requires different values of roof and ceiling insulation, depending on whether Option B or Option C is chosen. Table 11-7 shows a prescriptive requirements checklist for each option based on Table 170.2-A.

Table 11-7: Prescriptive Insulation Options

Source: California Energy Commission

Below Roof Deck Insulation (Option B). In a vented attic, air-permeable or air-impermeable insulation (batt, spray foam, loose-fill cellulose, or fiberglass) should be placed directly below the roof deck between the truss members and secured in place to provide a thermal break. Figure 11-2 shows an example of insulation details in an Option B attic. Insulation must be in direct contact with the roof deck and secured by the insulation adhesion, facing, mechanical fasteners, wire systems, a membrane material, or netting. Batts supported with cabling or other mechanical methods from below mustmust have supports that are less than or equal to 16” apart and no further than 8” from the end of the batt. Figure 11-3 shows the placement and provides example attachment methods for below-deck insulation.

When batt thickness exceeds the depth of the roof framing members, full-width batts must be used to fit snugly and allow batts to expand beyond the framing members. Full coverage of the top chord framing members by insulation is recommended as best practice but is not required.

Figure 11-2: Details of Option B Assembly

Figure 11-3: Placement of Insulation Below the Roof Deck

When insulation is installed below the roof deck to meet the prescriptive requirements of Option B, a radiant barrier is not required.

Vapor Retarders (Option B). Attic vapor retarders are not required by the Energy Code in most climates when using spray foam, blown-in insulation, or unfaced batts, and when sufficient attic ventilation is maintained. Although not required, the use of vapor retarders can provide additional security against possible moisture buildup in attic and framed assemblies. In climate zones 14 and 16, a Class I or Class II vapor retarder must be used to manage moisture as stated in the California Building Code (CBC), Title 24, Part 2.5, §R806.2.

Attic Ventilation (Options B and C)

Proper attic ventilation occurs at two points at the roof: the soffit (or eave) vents and the ridge vents.

When installing insulation below the roof deck, vent baffles and insulation barriers should be used to maintain proper ventilation space. Proper airflow through the space helps remove moisture and prevents any associated issues.

Where ceiling insulation is installed next to eave or soffit vents, a rigid baffle should be installed at the top plate to direct ventilation air up and over the ceiling insulation. (See Figure 11-4.) The baffle should extend beyond the height of the ceiling insulation and should have sufficient clearance between the baffle and roof deck at the top. There are several acceptable methods for maintaining ventilation air, including preformed baffles made of cardboard or plastic. In some cases, plywood or rigid foam baffles are used.

Figure 11-4: Baffles at the Eave in Attics

The California Building Code (CBC) requires a minimum vent area to be provided in roofs with attics, including enclosed rafter roofs that create cathedral or vaulted ceilings. Check with the local building jurisdiction to determine which of the two CBC ventilation requirements are to be followed:

1.    CBC, Title 24, Part 2, Vol. 1, Section 1203.2 requires that the net-free ventilating area mustmust not be less than 1/300 of the area of the space ventilated.

2.    CBC, Title 24, Part 2.5, Section R806.2 requires that the net-free ventilating area mustmust not be less than 1/150 of the area of the space ventilated. This ratio may be reduced to 1/300 if a ceiling vapor retarder is installed in climate zones 14 and 16.

If meeting Option 1 above, a minimum of 40 percent and not more than 50 percent of the vents must be located at least 3 feet (ft.) above the eave or cornice vents in the upper portion of the space being ventilated.

Insulation must not block the free flow of air, and a minimum 1-inch air space must be provided between the insulation and the roof sheathing and at the location of the vent.

Ventilated openings are covered with corrosion-resistant wire cloth screening or similar mesh material. When part of the vent area is blocked by meshes or louvers, the resulting net-free area of the vent must be considered to determine if ventilation requirements are met.

Many jurisdictions in California are covered by Wildland Urban Interface (WUI) regulations where specific requirements for construction materials must be used to improve building fire resistance. These regulations require special vents that are expressly tested to resist the intrusion of flame and embers. Check with the building department to ensure compliance with local codes.

Ducts and Air Handlers Located in Conditioned Space. Ducts may be located and verified to be in conditioned space instead of installing insulation at the roof deck. If complying with this option, ceiling and duct insulation must be installed at the values specified in Table 170.2-B for Option C, and a radiant barrier is required in most climate zones.

HERS Verification (Option C). Locating ducts in conditioned space does not alone qualify for this requirement; a HERS Rater must test and verify for low leakage ducts within conditioned space and verify that the ducts are insulated to a level required in Table 170.2-K of the Energy Code.

Design strategies that can be used to prescriptively comply with Option C include dropped ceilings (dropped soffit), plenum or scissor truss to create a conditioned plenum box, and open-web floor truss. The ducts and equipment must be within the air barrier of the building. Locating ducts within an unvented attic does not meet Option C requirements.

Ceiling Insulation (Options B and C). Insulation coverage should extend far enough to the outside walls to cover the bottom chord of the truss. However, insulation should not block eave vents in attics because the flow of air through the attic space helps remove moisture that can build up in the attic and condense on the underside of the roof deck. This can cause structural damage and reduce the effectiveness of the insulation.

Based on area-weighted averaging, ceiling insulation may be tapered near the eave, but it must be applied at a rate to cover the entire ceiling at the specified level. An elevated truss, or raised heel truss, is not required but may be desirable in some applications.

11.3.3.1    Performance Approach

In the performance approach, the standard design is based on the roof type. If the proposed design has an attic, prescriptive requirement Option B serves as the standard design, and Option D if there is no attic. An unvented attic must comply through the performance approach.

11.3.3.2    Radiant Barrier

11.3.3.3    Mandatory Requirements

The radiant barrier is a reflective material that reduces radiant heat transfer into the attic from solar heat gain in the roof. Radiant barriers must have an air space next to the foil side to provide its energy benefit. When a radiant barrier is installed, the product must meet mandatory requirements in §110.8(j). The radiant barrier must have an emittance of 0.05 or less. The product must be tested according to ASTM C1371 or ASTM E408 and must be certified by the California Bureau of Electronic and Appliance Repair, Home Furnishings and Thermal Insulation and listed in its Consumer Guide and Directory of Certified Insulation Material, at https://bhgs.dca.ca.gov/consumers/ti_directory.pdf.

11.3.3.4    Prescriptive Requirements

The prescriptive requirements call for Option C vented attics to have a radiant barrier in climate zones 2 through 15, while Option B vented attics require a radiant barrier in climate zones 2, 3, and 5 through 7.

Installation. The most common way of meeting the radiant barrier requirement is to use roof sheathing that has a radiant barrier bonded to it by the manufacturer. Some oriented strand board (OSB) products have a factory-applied radiant barrier. The sheathing is installed with the radiant barrier (shiny side) facing down toward the attic space.

Alternatively, a radiant barrier material that meets the same ASTM test and moisture perforation requirements that apply to factory-laminated foil can be field-laminated. Field lamination must use a secure mechanical means of holding the foil-type material to the bottom of the roof decking such as staples or nails that do not penetrate all the way through the roof deck material. Roofs with gable ends must have a radiant barrier installed on the gable ends to meet the radiant barrier requirement.

Other acceptable methods are to drape a foil type radiant barrier over the top of the top chords before the sheathing is installed, stapling the radiant barrier between the top chords after the sheathing is installed, and stapling the radiant barrier to the underside of the truss/rafters (top chord). For these installation methods, the foil must be installed with spacing requirements as described in Reference Appendices, Residential Appendix RA4.2.1.

Installation of radiant barriers is somewhat more challenging in the case of closed rafter spaces, particularly when roof sheathing is installed that does not include a laminated foil-type radiant barrier. Radiant barrier foil material may be field-laminated after the sheathing has been installed by laminating the foil to the roof sheathing between framing members. This construction type is described in the Residential Reference Appendices RA4.2.1.1. See Figure 11-5 for drawings of radiant barrier installation methods.

For closed rafter spaces, such as a cathedral ceiling, the required air space for radiant barriers must be provided and must meet the ventilation requirements of the California Building Code (CBC), Title 24, Part 2.5, Section R806.1.

Figure 11-5: Methods of Installation for Radiant Barriers

11.3.3.5    Performance Approach

In the performance approach, radiant barriers are modeled apart from the U-factor. The duct efficiency also is affected by the presence of a radiant barrier when using the performance approach.

11.3.3.6    Roofing Products

11.3.3.7    Roofing Products Mandatory Requirements

§10-113, 110.8(j)

See Section 3.2.4.1 for mandatory requirements for roofing products, rating and labeling, and field-applied liquid coatings applicable across multifamily and nonresidential buildings.

11.3.3.8    Roofing Products Prescriptive Requirements

Energy-efficient cool roofs are prescriptively required based on the roof slope and climate zones. The prescriptive requirements are based on aged solar reflectance and thermal emittance, or solar reflectance index (SRI), as summarized in Table 11-8. For steep-sloped roofs, the requirements also differ depending on whether roof/ceiling Option B, C, or D is selected. If a cool roof is being installed to comply with the Energy Code, it must meet the mandatory product and labeling requirements of Section 110.8(i) of the Energy Code.

Table 11-8: Prescriptive Cool Roof Requirements

Source: California Energy Commission

There are two exceptions to meeting these prescriptive requirements:

1.    Roof area with building-integrated photovoltaic panels or building-integrated solar thermal panels.

OR

2.    Roof constructions that have a weight of at least 25 pounds per square foot, including EPDM with stone ballast and slate roofing.

11.3.3.9    Roofing Products Performance Approach

The performance approach can be used to trade off the prescriptive cool roof requirements or increase solar reflectance or reduce emittance for additional credit.

If a manufacturer does not obtain a Cool Roof Rating Council (CRRC) certificate for its roofing products, the following default aged solar reflectance and thermal emittance values must be used for compliance:

1.          For asphalt shingles: 0.08 aged solar reflectance (ASR) and 0.75 thermal emittance (TE)

2.          For all other roofing products: 0.10 aged ASR and 0.75 TE

11.3.3.10  Wall Insulation

Requirements for wall U-factor and insulation are grouped by a combination of factors: wall assembly fire rating and construction type. In prescriptive requirements, all framed walls regardless of the framing material (wood, metal, or others) are subdivided into those with one-hour or lower fire rating and those with higher than one-hour fire rating. This allows high-fire rating (one-hour or higher) wall types, which have constructability limitations and are more costly to insulate, to adhere to less stringent U-factor requirements than walls with lower fire ratings (lower than one-hour).

Additionally, metal buildings and mass walls have their own subcategories for requirements.

11.3.3.11  Wall Insulation Mandatory Requirements

Above grade walls separating conditioned spaces from other spaces must adhere to the requirements below, based on the material, size, and location of the wall assemblies:

2x4 inch wood-framed walls above grade mustmust have a U-factor not exceeding 0.102. This requirement is met with at least R-13 insulation installed in the cavities between framing members.

2x6 inch or greater wood-framed walls above grade mustmust have a U-factor not exceeding 0.071. This requirement is met with at least R-20 insulation installed in the cavities between framing members.

Demising partitions and knee walls. Demising and knee walls must not exceed minimum U-factor requirements of 0.099 for wood framing and 0.151 for metal framing.

Metal building, mass walls, and spandrel panels and curtain wall. Each of the wall construction must not exceed the U-factor requirement in Table 11-9.

All other wall types (not listed) above grade must meet a maximum U-factor of 0.102.

Table 11-9: Wall Construction U-Factor Requirements

Source: California Energy Commission

11.3.3.12  Wall Insulation Prescriptive Requirements

The prescriptive requirements in Table 170.2-A for low fire rating (0-hour or 1-hour) framed walls are a U-factor of 0.051 in climate zones 1-5 and 8-16, and a U-factor of 0.065 in climate zones 6 and 7.

The U-factor requirements for high fire rating walls (1-hour or greater) are a U-factor of 0.059 for climate zones 1-5, 8-10, 12, and 13, and a U-factor of 0.051 for climate zone 11 and 14-16. U-factor requirements for climate zones 6 and 7 are 0.065 for both high fire rating and low fire rating framed walls.

A wall’s fire-resistance rating is determined by the fire code and is measured in hours. Chapter 6 of the California Building Code (CBC) describes fire-resistance rating in detail, and a building’s specific rating is ultimately decided upon by the local building official. The fire rating for a building’s exterior walls depends on the construction type, based on the building’s number of stories, building height, occupancy type, and fire-suppression system type. A wall’s fire-resistance rating can also vary due to fire-separation distance, though for residential occupancy types, fire-separation distance never changes a wall’s rating from 1-hour to 2-hour (or more). Code officials use CBC Tables 601, 602, 504.3 and 504.4 in combination to make the wall fire-rating determinations. The determination method is generally well understood, and fire-resistance rating info is readily available from the building’s architect. Generally, higher buildings with six or more stories and heavy-timber buildings have high fire-ratings, while low or mid-rise buildings of five or fewer stories have a low-fire rating. In most cases, all walls of a specific building will fall under one of the two categories used in Table 170.2-A.

The designer may choose any wall construction from Reference Appendices, Joint Appendix JA4 (Tables 4.3.1 and 4.3.4) that has a U-factor equal to or less than the prescribed level, depending on the climate zone.

Wood Frame. JA4 Table 4.3.1 shows that a 2x6 wood-framed wall at 16-inches-on-center can achieve a U-factor of 0.048 with R-21 batt insulation in the cavity and R-5 exterior insulation.

Metal Frame. Metal-framed assemblies will require rigid insulation to meet the maximum U-factor criteria. U-factors for metal-framed walls are given in Reference Appendices, Joint Appendix JA4 Table 4.3.4 and can be calculated using Energy Commission-approved compliance software.

Calculating U-factors. U-factors can be calculated by building the construction assembly in Commission-approved compliance software, including the inside finish, sheathing, cavity insulation, and exterior finish.

Light and Heavy Mass Walls by Heat Capacity. The prescriptive requirements have separate criteria for mass walls. Mass walls may be light or heavy mass walls depending on their heat capacity. Light mass walls have at least 7.0 and less than 15.0 Btu/ft²-°F, and heavy mass walls have at least 15.0 Btu/ft²-°F in heat capacity. Light mass walls have prescriptive requirement of U-factor not exceeding 0.077 and with additional R 13 interior insulation on the interior surface of the mass wall for climate zones 1-15. The requirements are more stringent in climate zone 16, with a U-factor if 0.059 and with R 17 interior insulation.

For heavy mass walls, the U-factor requirements are 0.650 for climate zones 2-5 and 10, 0.690 for climate zones 6-9, 0.184 for climate zones 11, 14-15, 0.253 for climate zones 1 and 12, 0.211 for climate zone 13, and 0.160 for climate zone 16.

Mass walls with insulation applied to both the interior and exterior, such as insulated concrete forms (ICF), must meet the requirements for mass walls with interior insulation. Placement of insulation on mass walls will affect the thermal mass properties of a building. When the prescriptive compliance approach is used, the continuous insulation must be installed integral with or on the exterior or interior of the mass wall.

Calculating the U-Factor. To calculate the effective U-factor of a furred wall using the tables in Reference Appendices, Joint Appendix JA4:

1.    Select a U-factor from JA4 Table 4.3.5 (Hollow Unit Masonry) or 4.3.6 (Solid Unit Masonry or Concrete) consistent with the type of wall.

2.    Select the appropriate effective R-value for interior or exterior insulation layers from JA4 Table 4.3.14.

3.    Use Equation 4-1, and the values selected, to calculate the U-factor of the construction assembly with the continuous insulation.

4.    Compare the U-factor; it must be equal to or greater than the mass prescriptive U-factor from Energy Code Table 170.2-A to comply.

The U-factor of furred concrete or masonry walls can also be determined by building the construction assembly in Commission-approved compliance software.

11.3.3.13  Raised-Floor Insulation

11.3.3.14  Raised-Floor Mandatory Requirements

Wood-framed floors over unconditioned space must have at least R-19 insulation installed between framing members, or the construction must have a U-factor of 0.037 or less. The equivalent U-factor is based on R-19 insulation in a 2x6, 16-inch on center wood-framed floor with a crawl space.

Other types of raised floors, except for concrete raised floors (concrete raised floors have a mandatory requirement of 0.269 maximum U-factor) must meet a maximum U-factor of 0.071. In all cases, some areas of the floor can have a U-factor greater than the requirement as long as other areas have a U-factor that is lower than the requirement and the area-weighted average U-factor is less than that described above.

Heated slab floors must meet special insulation requirements that are described in Section 11.1.9.5.

11.3.3.15  Raised-Floor Prescriptive Requirements

The prescriptive requirements differ for concrete raised floors and wood-framed floors. While the requirements for framed floors are the same in all climate zones, the requirements for (concrete) raised mass floors differ.

Wood Framed Raised Floors. The prescriptive U-factor requirement is the same as the mandatory level, at a maximum area-weighted U-factor of 0.037. Alternatively, the prescriptive requirement can be met by having a minimum of R-19 insulation installed between wood framing for framed raised floors in all climate zones.

Concrete Raised Floors. Concrete floors separating multifamily habitable space from a parking garage or other unconditioned spaces are considered exterior raised floors. Insulation requirements for concrete raised floors differ by climate zone, summarized in Table 11-10.

Table 11-10: Insulation Requirements for
Concrete Raised Floors per Table 170.2-A

Source: California Energy Commission

Other Raised Floors, including metal framed floors. The prescriptive U-factor is 0.048 in climate zone 1, and 0.39 in climate zones 2 and 14-16. In climate zones 3-13, the prescriptive requirement matches the mandatory requirement at 0.071 U-factor.

Installation. Floor insulation should be installed in direct contact with. the subfloor so that there is no air space between the insulation and the floor. Support is needed to prevent the insulation from falling, sagging, or deteriorating. Options for support include netting stapled to the underside of floor joists, insulation hangers running perpendicular to the joists, or other suitable means. Insulation hangers should be spaced at 18 inches or less before rolling out the insulation. Insulation hangers are heavy wires up to 48 inches long with pointed ends, which provide positive wood penetration. Netting or mesh should be nailed or stapled to the underside of the joists. Floor insulation should not cover foundation vents.

11.3.3.16  Slab Insulation

A.    Slab Insulation Mandatory Requirements

E.     Slab Insulation Products

The mandatory requirements state that the insulation material must be suitable for the application. Insulation material in direct contact with soil, such as perimeter insulation, must have a water absorption rate no greater than 0.3 percent when tested in accordance with ASTM C272 Test Method A, 24-Hour Immersion, and a vapor permeance no greater than 2.0 perm/inch when tested in accordance with ASTM E96.

The insulation must be protected from physical and UV degradation by either installing a water-resistant protection board, extending sheet metal flashing below grade, choosing an insulation product that has a hard durable surface on one side, or by other suitable means.

The top of the insulation must be protected with a rigid material to prevent intrusion of insects into the building foundation.

A common location for the slab insulation is on the foundation perimeter. Insulation that extends downward to the top of the footing is acceptable. Otherwise, the insulation must extend downward from the level of the top of the slab, down 16 inches (40 cm) or to the frost line, whichever is greater.

For below-grade slabs, vertical insulation mustmust be extended from the top of the foundation wall to the bottom of the foundation (or the top of the footing) or to the frost line, whichever is greater.

F.     Heated Slab Floor Insulation

Material and installation specifications for heat slab floors mustmust adhere to the following:

1.    Insulation values as shown in Table 110.8-A of the Energy Code

2.    Protection from physical damage and UV light deterioration

3.    Water absorption rate no greater than 0.3 percent (ASTM C272)

4.    Water vapor permeance no greater than 2.0 perm/inch (ASTM E96)

See Section 11.5.6.4 for more details.

B.    Slab Insulation Prescriptive Requirements

§170.2(a)5B, Table 170.2-A

Tables 170.2-A of the Energy Code require slab insulation for buildings up to three habitable stories but only for unheated slabs in climate zone 16. All heated slabs must meet mandatory insulation requirements in §110.8(g).

For unheated slabs in climate zone 16, a minimum of R-7 slab-edge insulation or a maximum U-factor of 0.58 must be achieved. The insulation must be installed to a minimum depth of 16 inches or to the bottom of the footing, whichever is less. The depth is measured from the top of the insulation, as near the top of slab as practical, to the bottom edge of the insulation.

Figure 11-16: Allowed Slab Edge Insulation Placement

Perimeter insulation is not required along the slab edge between conditioned space and the concrete slab of an attached unconditioned enclosed space such as a garage or covered patio.

11.3.3.17  Opaque Doors

An opaque door is an installed swinging door separating conditioned space from outside or adjacent unconditioned space with less than 25 percent glazed area. A door that has 25 percent or more glazed area is a glazed door and is treated like a fenestration product. The requirement is applicable to doors for individual dwelling units and in common use area.

Opaque dwelling unit entry doors between conditioned and unconditioned space are prescriptively required to have an area-weighted average U-factor no greater than U-0.20, per Table 170.2-A. Swinging common use entry doors on separating conditioned and unconditioned space prescriptively require a 0.70 U-factor. Swinging doors between unconditioned and conditioned space that are required to have fire protection are exempt from the prescriptive requirement. As an example, this may include a fire protection door that separate a conditioned dwelling units and unconditioned corridor space. Non-swinging entry doors for common use areas must have a 1.45 U-factor requirement to meet prescriptive requirements, except in climate zones 1 and 16 where the U-factor requirement is 0.50. The U-factor must be rated in accordance with NFRC 100, or the applicable default U-factor defined in Reference Appendices, Joint Appendix JA4, Table 4.5.1 must be used.

At the field inspection, the field inspector verifies that the door U-factor meets the energy compliance values by checking the NFRC label sticker on the product. When manufacturers do not rate the thermal efficiencies by NFRC procedures, the Energy Commission default values must be used and documented on a temporary default label. Default U-factors values for various door types are shown in Table 11-11.

Table 11-11: Default U-Factors for Doors per JA Table 4.5.1

Source: California Energy Commission

11.3.3.18  Vapor Retarder

In climate zones 14 and 16, a continuous Class I or Class II vapor retarder, lapped or joint sealed, must be installed on the conditioned-space side of all insulation in all exterior walls, on the roof decks of vented attics with above-deck or below-deck air-permeable insulation, and in unvented attics with air-permeable insulation.

Buildings with unvented or controlled-ventilation crawl spaces in all climate zones must have a Class I or Class II vapor retarder placed over the earth floor of the crawl space to reduce moisture entry and protect insulation from condensation in accordance with RA4.5.1.

Vapor retarder class is a measure of the ability of a material or assembly to limit the amount of moisture that passes through the material or assembly. Vapor retarder classes are defined in Section 202 of the California Building Code (CBC). Testing for vapor retarder class is defined using the desiccant method of ASTM E96.

1.    Class I: 0.1 perm or less

2.    Class II: 0.1 < perm < 1.0 perm

3.    Class III: 1.0 < perm < 10 perm

Following are common vapor retarder product types:

1.    Foil and other facings on gypsum board can provide moisture resistance, and product literature shows conformance to ASTM E96.

2.    Kraft paper facing on thermal batt insulation material is typically a Class II vapor retarder. Faced batts may have flanges for fastening to assembly framing. Fastening flanges may be face- or inset-stapled or not stapled at all, as the flanges provide no moisture control. Face stapling of flanged thermal batts helps ensure the insulation material is installed fully and properly within the framed cavity. Flangeless batts are also common and require no fastening as these materials maintain installation integrity through friction-fitting within the cavity of framed assemblies. In all cases, the insulation must be installed properly.

3.    Interior painted surfaces may also serve as vapor retarders if the paint product has been tested and shown to comply with the vapor retarder requirements. The effectiveness of vapor retarder paint depends upon the installed thickness (in mils). These products often require more than one layer to achieve the tested perm rating, and care must be shown by the installer of the paint and for inspection by the building official.

4.    Closed-cell spray polyurethane foam (ccSPF) products can provide Class I or Class II vapor retarder performance, depending on thickness.

For all types of vapor retarders, care should be taken to seal penetrations, such as electric outlets on exterior walls.

Figure 11-7: Typical Kraft-faced Vapor Retarder Facing

11.3.3.19  Mandatory Air Sealing and Air Leakage

A.    Joints and Other Openings

See Section 3.2.3.1 for requirements related to infiltration and air leakage applicable across multifamily and nonresidential buildings.

B.    Fireplaces, Decorative Gas Appliances, and Gas Logs

Closeable metal or glass doors must cover the entire firebox opening for fireplaces, decorative gas appliances, and gas logs in dwelling unit and common use areas. A combustion air intake no smaller than 6 square inches in area, with a tight-fitting damper or combustion-air control must also be installed. A flue damper with accessible control is also required.

11.3.3.20  Quality Insulation Installation (QII)

11.3.3.21  QII Prescriptive Requirements

All insulation mustmust be installed according to manufacturer specifications, throughout the building. In multifamily buildings up to three habitable stories, a third-party HERS Rater is required to verify the integrity of the installed insulation. The installer mustmust provide evidence to the HERS Rater using compliance documentation that all insulation specified is installed to meet specified R-values and assembly U-factors.

To meet QII, two primary installation criteria must be adhered to, and they both must be field-verified by a HERS Rater. They include air sealing of the building enclosure (including walls, ceiling/roof, and floors), as well as proper installation of insulation. Refer to Reference Appendices, Residential Appendix RA3.5 for more details.

Many multifamily insulation installations have flaws that degrade thermal performance. Four problems are generally responsible for this degradation

1. There is an inadequate air barrier in the building envelope or holes and gaps within the air barrier system that allow air leakage.

2. Insulation is not in contact with the air barrier, creating air spaces that short-circuit the thermal break of the insulation.

3. The insulation has voids or gaps, resulting in portions of the construction assembly that are not properly insulated and, therefore, have less thermal resistance than other portions of the assembly.

4. The insulation is compressed, creating a gap near the air barrier and/or reducing the thickness of the insulation.

QII requires third-party HERS inspection to verify that an air barrier and insulation are installed correctly. Guidance for QII is provided in the Reference Appendices, Residential Appendix RA3.5. QII applies to framed and non-framed assemblies, including the following:

Table 11-12: Framed Assemblies vs. Non-Framed Assemblies

Source: California Energy Commission

Table 11-13 provides information on applicability and installation tips and examples for QII practices.

Table 11-13: Installer Tips for Implementing QII

Source: California Energy Commission

A.    Air Barrier

An air barrier mustmust be installed enclosing the entire building. The air barrier must be installed in a continuous manner across all components of framed and non-framed envelope assemblies. The installer mustmust provide evidence with compliance documentation that the air barrier system meets one or more of the air barrier requirements. More detailed explanation is provided in Reference Appendices, Residential Appendix RA3.5. Documentation for the air barrier includes product data sheets and manufacturer specifications and installation guidelines.

As part of QII for multifamily buildings up to three habitable stories, a third-party HERS Rater is required to verify that the air barrier has been installed properly and is integral with the insulation being used throughout the building.

B.    QII Performance Requirements

When using the performance approach for a multifamily building up to three habitable stories, QII may be traded off with other efficiency features. However, the compliance modeling software assumes QII and full insulation effectiveness in the standard design. The compliance modeling software automatically reduces the effectiveness of insulation for the proposed design in projects that do not pursue QII, with the assumption that QII results in a properly installed system. Poor installation practices compromise the effectiveness of the air barrier and insulation products and results in worse envelope thermal performance than assumed in the standard design.

Similar increases in heat loss and heat gain are experienced for roof/ceilings where construction and installation flaws are present. The reduction in effectiveness reflects standard industry installation practices and allows for full insulation credit to be taken for HERS verified quality insulation installation.

QII is not a compliance option for multifamily buildings with four or more habitable stories.

11.3.3.22  Advanced Opaque Envelope Options Requiring the Performance Approach

The performance approach offers increased flexibility and compliance credits for certain assemblies. For buildings up to three habitable stories this often includes compliance credits requiring HERS verification. The proposed design used under the performance approach is compared to the standard design, which is determined by the prescriptive requirements. This section describes several envelope assemblies and techniques that require use of the performance approach. See the Residential Compliance Manual Section 3.6 for extensive detailed descriptions and illustrations.

Advanced Building Practices. Common strategies for exceeding the minimum energy performance level set by the 2022 Energy Code include:

•    Higher insulation levels.

•    More efficient fenestration.

•    Reduced building infiltration.

•    Use of cool roof products.

•    Better framing techniques (such as the use of raised-heel trusses that accommodate more insulation).

•    Reduced thermal bridging across framing members.

•    Use of non-framed assemblies or panelized systems (such as SIPs and ICFs).

•    More efficient heating, cooling, and water-heating equipment.

11.3.3.23  Alternative Construction Assemblies

This section describes several advanced construction assemblies. These three assemblies are included in the Reference Appendices, Joint Appendix JA4 U-factor tables for use in the compliance software.

Structural Foam Wall Systems The high performance structural foam wall assembly is an advanced assembly system that consists of closed cell spray polyurethane foam (ccSPF) placed in the cavity bonded to wood framing and continuous rigid board insulation on the exterior of the frame. The bond that occurs between the ccSPF, the framing, and the continuous rigid insulation can provide code-compliant wind and seismic structural load resistance without the use of OSB sheathing

A builder can configure the thicknesses of the cavity ccSPF, rigid insulation, and alternative cavity insulation to attain U-factors of 0.050 or better in 2x4 at 24” on center assembly. The structural foam wall assembly can be combined with advanced framing techniques to increase energy and resource efficiency while reducing material and labor costs.

Structural Insulated Panels (SIPs) Structural insulated panels (SIPS) are a non-framed advanced construction system that consists of rigid foam insulation sandwiched between two sheets of board. The board can be sheet metal, plywood, cement, or oriented strand board (OSB), and the foam can be expanded polystyrene foam (EPS), extruded polystyrene foam (XPS) or polyurethane (PUR), or polyisocyanurate (ISO) foam. Little or no structural framing penetrates the insulation layer.

SIPs combine several components of conventional building, such as studs and joists, insulation, vapor barrier, and air barrier. They can be used for many different applications, such as exterior walls, roofs, floors, and foundation systems. Reference Appendices, Joint Appendix JA4 Table 4.3.2 has U-factors for SIPS wall assemblies, and JA4 Table 4.4.3 has U-factors for SIPS floor constructions. U-factors used for compliance must be taken from these tables or by using Commission-approved compliance software.

Insulating Concrete Forms (ICF) Insulating concrete forms (ICFs) are a system of interlocking formwork for concrete that stays in place as permanent building insulation and can be used for cast-in-place reinforced above- and below-grade concrete walls, floors, and roofs. The insulating panels are made from expanded polystyrene (EPS) and extruded polystyrene (XPS) rigid insulation boards, polyurethane (PUR), composites of cement and EPS, and composites of cement and shredded wood fiber. ICF wall assemblies provide three energy efficiency benefits:

1.    Continuous rigid insulation on both sides of a high-mass core

2.    Elimination of thermal bridging from wood framing components

3.    A high degree of airtightness inherent to this method of construction

The thermal aspects of ICFs are represented in Reference Appendices, Joint Appendix JA4 Table 4.3.13. 

B.    Advanced Wall Framing

Advanced wall systems (AWS), or advanced framing, refer to a set of framing techniques and practices that minimize the amount of wood necessary to build a structurally sound, safe, durable, and energy-efficient building. AWS improves energy and resource efficiency while reducing first costs.

Reducing the amount of framing (wood or metal) in exterior walls improves energy efficiency with more insulation, a reduced framing factor and reduced thermal bridging. The standard framing factor for a wood-framed 2x4 wall at 16” on center is 25 percent. When AWS is used, the framing factor is reduced to 17 percent, reflecting improved energy performance.

Double and Staggered Wall Assemblies. Double-wall and staggered-wall systems were developed to better accommodate electrical and plumbing systems, allow higher levels of insulation, and provide greater sound reduction. The advantages of these types of wall systems are:

1.    Smaller dimensional lumber can be used.

2.    It is easier to install insulation properly.

3.    It eliminates thermal bridging through the framing.

4.    It reduces sound transmission through the wall.

11.3.3.24  Roofs

Roof techniques and assemblies required to use the performance approach include:

•    Unvented attics

•    Above-deck insulation

•    Insulated roof tiles

•    Raised heel, extension truss, or energy truss

•    Nail base insulation panels

11.3.3.25  Unvented Attics

Attic ventilation is the traditional way of controlling temperature and moisture in an attic. In an unvented attic assembly, insulation is applied directly at the roofline of the building, either above or below the structural roof rafter. The roof system becomes part of the insulated building enclosure. The thermal boundary of the building results in an unvented attic space between the ceiling gypsum board and the insulated roof above.

Gable Ends in Unvented Attics. In unvented attics, where insulation is applied directly to the underside of the roof deck, framing for gable ends that separate the unvented attic from the exterior or unconditioned space should be insulated to meet or exceed the wall R-value of the adjacent exterior wall construction. The side of air-permeable insulation exposed to the unconditioned attic space should be completely covered with a continuous air barrier.

11.3.3.26  Above-Deck Insulation

Above-deck insulation requires insulation above the roof rafters, directly in contact with the roof deck to improve thermal integrity of the roof system. An air space between the roofing and the roof deck provides additional benefit. Above-deck insulation can be implemented with either asphalt shingles or clay/concrete tiles. Details for above-deck insulation details differ depending on the type of roof tiles. Refer to the Residential Compliance Manual Section 3.6 for detailed descriptions. 

11.3.3.27  Insulated Roof Tiles (IRT)

Insulated roof tile (IRT) can improve the thermal performance of the roof assembly and lower attic temperatures. IRT combines concrete or clay tiles with insulation as a packaged product. Most of the increase in R-value is due to the integration of insulation into the roofing product itself. Additional thermal performance can be gained by combining IRT with rigid foam insulation inserts. These tiles are lighter than typical roof tiles and have better thermal performance than traditional tiles due to the insulating core. IRT can reduce radiant losses and maintain warmer roof deck temperatures, thereby reducing the potential for condensation.

11.3.3.28  Raised Heel, Extension Truss, or Energy Truss

Raised heel or extension trusses allow full depth, uncompressed insulation at the ceiling to continue to the ceiling edge where the wall and ceiling meet. The roof truss is assembled with an additional vertical wood framed section at the point where the truss bears on the wall. The vertical section raises the top chord and provides increased space that can be filled with insulation. See Figure 11-9 for details of a raised heel truss. Benefits of this strategy include:

•    Realizing the full benefit of ceiling insulation.

•    Providing more space for air handler and duct systems if located in the attic.

Similar construction methods include framing with a rafter on a raised top plate or using spray foam or rigid foam at the edge.

Figure 11-9: Standard Truss vs. Raised Heel Energy Truss

Source: California Energy Commission

11.3.3.29 

11.3.3.30  Nail Base Insulation Panel

The nail base insulation panel is a deck insulation strategy that consists of exterior-facing OSB, or other structural sheathing laminated to continuous rigid insulation, which is fastened directly to roof framing (Figure 11-10). This saves the time and expense of installing a structural sheathing layer above and below the rigid insulation. The nail base insulation panel creates a nailing surface for attaching roof cladding. Suitable for vented and unvented attic assemblies, the exposed underside of the rigid insulation has a facer that provides a radiant barrier, as well as ignition/thermal barrier protection as required by code.

Figure 11-10. Nail Base Insulation Panel with Radiant Barrier Affixed to Trusses in A Vented Attic Configuration

11.3.3.31  Thermal Mass

Thermal mass consists of exposed mass walls, tiled or exposed concrete floors and other heavy elements within the building envelope that can help stabilize indoor temperatures.

Mass walls typically fall into two categories:

•    Masonry. Masonry includes solid or hollow-core clay and concrete units. Concrete masonry units (CMU) are made from a mixture of Portland cement and aggregates under controlled conditions. Other masonry unit types include cast stone and calcium silicate units.

•    Concrete and concrete sandwich panels. Concrete and concrete sandwich panels typically use a precast form by casting concrete in a reusable mold or "form" that is then cured in a controlled environment, transported to the construction site, and lifted into place. Precast stone is distinguished from precast concrete by using a fine aggregate in the mixture, giving the appearance of naturally occurring rock or stone.

When the performance method is used, credit is offered for increasing thermal mass in buildings. This procedure is automated in Energy Commission-approved compliance software.

11.3.4      Fenestration

The size, orientation, and types of fenestration products, such as windows, glazed doors, dynamic glazing, window films, and skylights, have a significant impact on energy use and heating and cooling loads in the building and can dramatically affect the overall energy performance of a building.

Any door that is 25 percent or greater glass is considered a glazed door and must comply with the mandatory requirements and other requirements applicable to a fenestration product. Vertical fenestration in demising walls (between conditioned spaces) are required to comply with the area-weighted average U-factor requirement in Table 170.2-A.

Several factors affect window performance. For fenestration with NFRC ratings, the following performance features are accounted for in the U-factor and SHGC ratings:

Frame materials, design, and configuration (including cross-sectional characteristics). Fenestration can be framed in many materials. The most common include vinyl, wood, fiberglass, aluminum, or composites of these materials. Frames made of low-conductance materials like wood, vinyl, and fiberglass are better insulators than metal. Some aluminum-framed units have thermal breaks that reduce the conductive heat transfer through the framing element compared with similar units having no such conductive thermal break.

Number of panes of glazing, low-emissivity (low-e) coatings, tints, fill gases, cavity dimensions, and spacer construction. Windows compliant with the prescriptive requirements are likely to have at least double-glazing with a low-emissivity (low-e) coating and argon gas fill with an improved spacer. The choice of low-e coating is particularly important as cooling climates will generally benefit from a low SHGC coating, while heating climates may benefit from a high SHGC coating. Adding glazing layers such as triple glazing and low-emissivity coatings such as those facing the conditioned space are two likely improvements.

Window components, such as tints and coatings, reduce visual transmittance (VT), reducing light to interior spaces and increasing energy for interior lighting. VT requirements for multifamily buildings four or more habitable stories allow for daylighting and daylighting controls on interior light fixtures.

11.3.4.1    Fenestration Types

Section 3.3.1 includes fenestration and category definitions applicable across nonresidential and multifamily buildings. Prescriptive multifamily fenestration requirements depend on which of the following window types are installed.

•    Curtainwall, window wall, or storefront windows consist of metalized or glass panels often hung outside structural framing to create exterior wall elements around fenestration and between floors.

•    NAFS Performance Class AW (architectural windows) adhere to industry standard – AAMA/ WDMA/ CSA 101/ I.S.2/ A440 NAFS-2017 North American Fenestration Standard/ Specification, which includes testing requirements for fenestration products based on air leakage resistance, water penetration resistance, uniform load resistance and forced-entry resistance. The Performance Classes are designated R, LC, CW, and AW in order of performance. Higher rated products typically rely on metal window framing materials which lead to high thermal bridging in the window frame and thus higher U-factors. Windows must be certified as NAFS rated to qualify for the category.

Performance Class AW windows are significantly more expensive than lower-rated products and are unlikely to be specified unless necessary. The architect calculates the building’s wind loads to determine if Class AW windows are needed. There is no specific code that regulates this decision. It is ultimately at the discretion of the architect and building owner.

•    All other fenestration includes operable windows, punched fixed windows, glass doors, and skylights that do not qualify as NAFS Performance Class AW.

11.3.4.2    Fenestration Mandatory Requirements

§110.6(a)5, Table 110.6-A|topic=TABLE 110.6-A DEFAULT FENESTRATION PRODUCT U-FACTORS, 160.1(e)

Mandatory requirements for fenestration products, labeling, and air leakage for multifamily and nonresidential buildings are covered in Section 3.3.2.

The area-weighted U-factor of all fenestration, including skylights, may not exceed 0.58.

Exception for Greenhouse/Garden Windows. Compared to other fenestration products, the NFRC-rated U-factor for greenhouse windows are comparatively high. Section 160.1(e)1 includes an exception from the U-factor requirement for dual-glazed greenhouse or garden windows that total up to 30 ft² of rough opening area per dwelling unit.

11.3.4.3    Fenestration Prescriptive Requirements

11.3.4.4    Fenestration Area

Multifamily buildings have three prescriptive fenestration area limitations. All three must be met for prescriptive compliance.

1.    Total combined vertical fenestration and skylight area may not exceed 20 percent of the conditioned floor area (CFA)

2.    Total vertical fenestration may not exceed 40 percent of the gross exterior wall area.

3.    Total skylight area may not exceed 5 percent of the gross exterior roof area.

11.3.4.5    Fenestration Properties

Prescriptive fenestration requirements, for vertical and skylight fenestration, for multifamily buildings refer to Table 170.2-A. The maximum fenestration U-factor and maximum relative solar heat gain coefficient (RSHGC), and minimum visible transmittance (VTT depend on window type and climate zone. The required RSHGC additionally depends on whether a multifamily building is three or fewer or four or more habitable stories. Only buildings with four or more habitable stories are subject to VT requirements.

Relative solar heat gain coefficient (RSHGC) allows for an external shading correction from exterior shading devices and overhangs. A fenestration product with an SHGC greater than prescriptively required may qualify if an opaque exterior shading device or overhang is used and the combined area-weighted average complies with the prescriptive requirements. Balconies that extend above glazing are common overhangs in multifamily buildings. See Section 3.3.3 for more information about SHGC and Overhang Factor.

For credit, exterior shading devices must be permanently attached as opposed to being attached using clips, hooks, latches, snaps, or ties.

The window property requirements for each fenestration type are as follows.

Curtainwall or storefront fenestration has a maximum U-factor of 0.38 in Climate Zones 1 and 16 and 0.41 in Climate Zones 2 through 15. For multifamily buildings with four or more habitable stories, the maximum RSHGC is 0.35 in Climate Zone 1, 0.26 in Climate Zones 2 through 13 and 15, and 0.25 in Climate Zones 14 and 16. Multifamily buildings up to three habitable stories in Climate Zones 1, 3, 5, and 16 have no RSHGC requirements. Minimum VT is 0.46 across all climate zones for buildings with four or more habitable stories.

Performance Class AW rated fenestration has a maximum U-factor of 0.38 in Climate Zones 1 and 16 and 0.40 in Climate Zones 2 through 15. The maximum RSHGC in Climate Zone 1 is 0.35 and 0.24 in all other climate zones. Multifamily buildings up to three habitable stories in Climate Zones 1, 3, 5, and 16 have no RSHGC requirements. Minimum VT is 0.37 across all climate zones for buildings with four or more habitable stories.

All other fenestration has a maximum U-factor of 0.30 in Climate Zones 1 through 5 and 8 through 16 and 0.34 in Climate Zones 6 and 7. The maximum RSHGC is 0.23 for buildings in Climate Zones 2, 4, and 6 through 15. Multifamily buildings up to three habitable stories in Climate Zones 1, 3, 5, and 16 have no RSHGC requirements. There is no VT requirement for fenestration in the “all other” category.

The requirements apply to fenestration products without consideration of insect screens or interior shading devices. With some exceptions, some fenestration products may exceed the prescriptive requirement as long as the U-factor and RSHGC of windows, glazed doors, and skylights can be area weight-averaged together to meet the prescriptive requirement using the certificate of compliance document in Appendix A of this manual.

See Table 170.2-A for summarizes of climate zone-specific prescriptive requirements by fenestration type.

Exceptions to the prescriptive fenestration requirements include:

•    Glazed Doors. Each new dwelling unit may have up to 3 ft2 of glass in a door that do not meet the prescriptive U-factor and RSHGC requirements.

•    Skylights. Each new dwelling unit with roof area may have up to 16 ft2 of skylight area that does not meet the prescriptive U-factor and SHGC requirements. The exempted skylight must have a maximum 0.55 U-factor and a maximum SHGC of 0.30. See Exception 2 of §170.2(a)3Bii.

•    Chromogenic Glazing. If a multifamily building includes chromogenic type glazing that is automatically controlled, the lowest U-factor and lowest SHGC must meet the prescriptive requirements. This type of product cannot be weight averaged with nonchromogenic products as per Exception to Section 170.2(a)3Bii and Section 170.2(a)3Biii.

•    Bay Windows. Bay windows with no rating for the entire unit (where there are multiple windows that make up the bay) and with factory-installed or field-installed insulation must comply accounting for the performance characteristics of each component separately.

First story display perimeters and where overhangs are prohibited by code can have a maximum RSGHC of 0.56 and do not need to meet the RSHGC requirements in Table 170.2-A. U-factor and VT requirements of Table 170.2-A apply.

11.3.4.6    Fenestration in the Performance Approach

The performance approach offers increased flexibility as well as compliance credits for high performance fenestration. The compliance software compares whole building energy use, as calculated with the proposed window properties, area, and orientation, to whole building energy use as calculated with prescriptive U-factor and RSHGC values. The following are fenestration strategies for improved energy performance.

A.    Fenestration Area and Orientation

The performance approach accounts for fenestration area and orientation, which impact energy use. The standard design window orientations match the proposed design. While there is no compliance credit for window placement across orientations, window placement to avoid solar heat gain will result in lower cooling loads and can lower the overall energy budget in the building and therefore reduce the size of the solar PV system required to offset energy use.

For buildings with glazing areas less than or equal to 20 percent of the conditioned floor area (CFA) and less than or equal to 40 percent of the exterior wall area, the standard design fenestration for a newly constructed building is modeled with the same glazing area as the proposed building. For buildings with more than 20 percent of the CFA or more than 40 percent exterior wall area, the standard design glass area is limited to the lower of 20 percent of the CFA or 40 percent of the exterior wall area. The software reduces fenestration area proportionate to total fenestration area across each orientation in the standard design.

B.    Improved Fenestration Performance

The fenestration weighted average U-factor and RSHGC in the standard design for newly constructed buildings is defined in Table 170.2-A, dependent on window type and climate zone. High-performance fenestration that performs better than the prescriptive requirements provide credit through the performance method. The magnitude of the effect of a lower U-factor will vary by climate zone. In mild coastal climates, the benefit from reducing fenestration U-factor will be smaller than in more extreme climates. In hot climates, choosing a window with an SHGC lower than prescriptively required will reduce the cooling loads compared to the standard design. Window film and dynamic glazing are also two options for improved window performance. Section 3.3.3.2 incudes more information on these options.

C.    Fixed Permanent Shading Devices

Overhangs or side fins that are attached to the building and shading from the building itself can be accounted for in the performance approach and impact building heating and cooling loads. See Section 3.5.1.4 for more information on modeling overhangs and vertical shading fins.

11.3.5      Daylighting

Enclosed conditioned and unconditioned spaces greater than 5,000 ft² and with ceiling heights exceeding 15 feet must meet daylighting requirements as described in Section 3.3.4.2E.

11.3.6      Additions and Alterations

11.3.6.1    Additions

Additions to all multifamily building dwelling units and common use areas mustmust meet the mandatory envelope requirements for newly constructed buildings including:

•    Ceiling and roof insulation (see Section 11.1.8.20)

•    Wall insulation (See Section 11.1.9.30)

•    Floor insulation (See Section 11.3.1.6A and 11.1.9.5A)

•    Vapor retarder (See Section 11.1.9.7)

•    Fireplace, decorative gas appliances, and gas log provisions (See Section 11.1.9.8)

•    Fenestration U-factor of 0.58 (See Section 11.1.10.2)

Prescriptive requirements for additions match those for newly constructed buildings (See Sections 11.1.8 and 11.1.10) with some modifications that depend on the conditioned floor area of the addition.

For additions greater than 700 square feet (ft²):

•    Fenestration area must not exceed 175 square feet or 20 percent of the addition floor area.

•    Extensions of existing framed walls may retain the dimensions of the existing wall. In these cases, R-15 insulation must fill cavities in 2x4 stud walls and R-21 in 2x6 stud walls.

•    If siding is not removed during construction, no continuous insulation is required on existing walls. In these cases, R-15 insulation must fill cavities in 2x4 stud walls and R-21 in 2x6 stud walls.

•    The air sealing elements of QII are not required in cases where unconditioned space is being converted to conditioned space when the existing air barrier is not being removed or replaced.

•    Additions that increase the area of the roof by 2,000 square feet or less are exempt from the solar ready requirements of Section 160.8.

For additions 700 square feet or less:

•    Overall roof and ceiling assemblies are required to achieve an overall U-factor of 0.025 or less in Climate Zones 1,2,4, and 8-16 and a U-factor of 0.031 in Climate Zones 3, 5, 6, and 7. A wood framed assembly would need R-38 insulation to achieve a 0.025 U-factor and R-30 insulation for a 0.031 U-factor.

•    Radiant barrier is required in buildings up to three habitable stories in Climate Zones 2-15.

•    Extensions of existing framed walls may retain the dimensions of the existing wall. In these cases, R-15 insulation must fill cavities in 2x4 stud walls and R-21 in 2x6 stud walls.

•    Fenestration U-factor, RSHGC, and VT must meet requirements of Table 180.2-B (See Section 11.1.12.2)

•    QII is not required.

•    Additions up to 300 sq. ft. are exempt from the prescriptive roof product requirements.

11.3.6.2    Alterations

11.3.6.3    Roof Alterations

Roofs with more than 50 percent of the roof area or 2,000 square feet of roof (whichever is less) being recovered or recoated are required to have minimum aged solar reflectance and thermal emittance, or solar reflectance index (SRI), determined by slope and climate zone. Low-sloped roofs in Climate Zones 2, 4, and 6 through 15 mustmust have a minimum aged solar reflectance of 0.63 and a minimum thermal emittance of 0.75, or a minimum SRI of 75. This requirement may alternatively be met through roof deck insulation, as summarized by Climate Zone in Table 11-14. Climate Zones 1, 3, and 16 do not have cool roof requirements.

Table 11-14: Roof/Ceiling Insulation Tradeoff for Low-Sloped Aged Solar Reflectance (Table 180.2-A)

Source: California Energy Commission

Steep-sloped roofs in Climate Zones 4 and 8 through 15 require a minimum aged solar reflectance of 0.20 and a minimum thermal emittance of 0.75, or a minimum SRI of 16. Equivalence may be demonstrated through:

•    A 0.025 U-factor ceiling assembly; or

•    An attic radiant barrier, not installed directly above spaced sheathing; or

•    R-2 or greater insulation above or below the roof deck; or

•    No ducts in the attic in Climate Zones 2, 4, 9, 10, 12, or 14.

Roof area covered by building integrated photovoltaic panels or building integrated solar thermal panels is not required to meet the minimum requirements for aged solar reflectance and thermal emittance, or SRI. Roof constructions with a weight of at least 25lb/ft² are also exempt from the aged solar reflectance and thermal emittance or SRI requirement.

In Climate Zones 1,2,4, and 8 through 16, low-sloped roofs mustmust additionally be insulated to R-14 continuous insulation or 0.039 U-factor. Roofs with new R-10 insulation above deck are exempt from this requirement.

Vented attics in Climate Zones 1-4 and 8-16 are required to have insulation installed to a weighted U-factor or 0.020, or R-49 ceiling insulation. Buildings with existing R-19 or greater insulation at the ceiling level in Climate Zones 1, 3, 4, and 9 are exempt from this requirement.

Vented attics in Climate Zones 2 and 11-16 are required to air seal accessible areas of the ceiling plane between the attic and conditioned space per §110.7|topic=SECTION 110.7 – MANDATORY REQUIREMENTS TO LIMIT AIR LEAKAGE. Dwelling units with existing R-19 or greater insulation at the ceiling level are exempt from this requirement. Dwelling units with atmospherically vented space or water heating appliances within the pressure boundary of the dwelling unit are also exempt.

In vented attics in Climate Zones 1-4 and 8-16, recessed downlight luminaires in the ceiling mustmust be covered with insulation to the same depth as the rest of the ceiling. Luminaires not rated for insulation contact must be replaced or fitted with a fire-proof cover that allows for insulation to be installed directly over the cover. Dwelling units with existing R-19 or greater insulation at the ceiling level are exempt from this requirement in Climate Zones 1-4 and 8-10.

Attic ventilation must comply with California Building Code (CBC) requirements.

Exemptions for the roof insulation requirements for ventilated attics include:

•    Dwelling units with at least R-38 existing insulation installed at the ceiling level

•    Dwelling units where the alteration would directly cause the disturbance of asbestos

•    Dwelling units with knob and tube wiring located in the attic

•    Where the accessible space in the attic is not large enough to accommodate the required R-value, the entire accessible space mustmust be filled with insulation

•    Where the attic space above the altered dwelling unit is shared with other dwelling units and the requirements are not triggered for the other dwelling units.

11.3.6.4    Wall Alterations

Walls separating conditioned space from unconditioned space, with the exception of mass walls, must be insulated to a mandatory minimum R-value between framing members or area-weighted U-factor, dependent on the assembly type:

•    Metal building walls: R-13 insulation or 0.113 assembly U-factor

•    Metal framed walls: R-13 insulation or 0.217 assembly U-factor

•    Wood framed and other walls: R-11 insulation or 0.110 assembly U-factor

•    Spandrel panel and curtain walls: R-4 insulation or 0.280 assembly U-factor

11.3.6.5    Floor Alterations

Floors separating conditioned space from unconditioned space must be insulated to a mandatory minimum R-value or area-weighted U-factor, dependent on the assembly type:

•    Raised framed floors: R-11 insulation or 0.071 U-factor

•    Raised mass floors: R-6 insulation or 0.111 U-factor

11.3.6.6    Fenestration Alterations

The area-weighted U-factor of all fenestration, including skylights, may not exceed the mandatory maximum of 0.58.

Alterations that replace existing fenestration of the same total area can meet prescriptive requirements by meeting the maximum U-factor, RSHGC, ad VT requirements of Table 180.2-B for each window replaced or an area weighted U-factor and RSHGC across all replaced windows from Table 170.2-A. Where 150 square feet or less of the building's vertical fenestration is replaced, the building is exempt from the RSHGC and VT requirements.

Alterations that add fenestration are required to meet the total fenestration area requirements and the U-factor, RSHGC, and VT requirements of §170.2(a)3 and Table 170.2-A. Alterations that add vertical fenestration area of up to 50 ft² to the building are exempt from this requirement. Alterations that add skylight area up to 16 ft² to the building are exempt from fenestration area and Table 170.2-A requirements but may meet not exceed a U-factor of 0.55 or an RSHGC of 0.30.

See Section 11.1.10.3 for Table 170.2-A requirements. See Table 180.2-B for Altered Fenestration Maximum U-Factor and Maximum SHGC.

11.3.6.7    Door Alterations

Alterations that add exterior door area mustmust meet the U-factor requirement of §170.2(a)4 (See Section 11.1.9.6).

11.3.7      Code in Practice

11.3.7.1    Garden Style Multifamily Case Study

The Garden Style Multifamily Case Study considers a new two-story garden style multifamily building in Burbank, California (Climate Zone (CZ) 9). This is a sample project created for training purposes, and it consists of 7,216 ft² of conditioned floor area with eight dwelling units and no common use areas. The case study tables in this chapter compare the proposed building envelope features to Mandatory and Prescriptive Energy Code requirements and evaluate possible compliance options.

Figure 11: Garden Style Multifamily: South (Front) and West (Left) Elevations

Figure 12: Garden Style Multifamily: North (Rear) and East (Right) Elevations

Figure 14: Garden Style Multifamily: 1st Floor, 1-Bedroom Apartment

Table 11-15: Garden Style Multifamily Case Study Compared to Mandatory and
Prescriptive Envelope Requirements (Climate Zone 9)
Total Conditioned Floor Area and Fenestration

Table 11-16: Roof, Wall, and Floor, plus Verifications Case Studies

Roof and Ceiling: Insulation, Radiant Barrier and Roofing

Wall Insulation

Floor Insulation

Source: California Energy Commission

Note that the 2022 Energy Code has a new prescriptive calculation method for total allowed fenestration area. Instead of requiring either a percentage of the conditioned floor area or a percentage of the gross wall area, the 2022 Energy Code limits multifamily buildings to the smaller of 20 percent of the conditioned floor area and 40 percent of the gross exterior wall area. In this example, 20 percent of the conditioned floor area equals 1,443 ft² and 40 percent of the exterior wall area equals 1,959 ft², so the Prescriptive total fenestration area cannot be more than 1,443 ft². The proposed total fenestration area is only 700 ft², so it meets the Prescriptive requirement.

The building envelope meets all mandatory requirements and some prescriptive requirements except for the exterior wall insulation and the roof design in combination with the duct location.

The exterior framed walls for this example building need a U-factor less than or equal to 0.051 to comply with the prescriptive approach, but the proposed design has framed wall U-factor equal to 0.065. Per Reference Appendices. Joint Appendix JA4 Table 4.3.1(a) one option for Prescriptive compliance would be to add R-4 continuous insulation to the planned wall assembly for a U-factor of 0.049.

The proposed design has ducts in a vented attic with R-30 ceiling insulation, but no roof insulation. Prescriptive Option B allows ducts in the attic, but that option also requires ceiling insulation, below-deck roof insulation, and an air space between the roofing material and the roof sheathing. Prescriptive Option C allows just ceiling insulation, but only if the ducts and the air handling units are all in conditioned space. The design team could make changes to the roof design or duct location to comply prescriptively, but they may not want to.

If the design team chooses to keep the original wall insulation and proposed roof construction combined with duct location, then the project will need to show compliance using the Performance Approach.

Figure 14: R-21 Framed Wall and R-30 Attic Roof Details

11.3.7.2    Mid-Rise Multifamily Case Study

The Mid-Rise Multifamily Case Study covers a new five-story multifamily building in Sacramento, California (Climate Zone (CZ) 12). This is a sample project created for training purposes, and it includes 112,044 square feet (ft²) of conditioned floor area with 88 dwelling units, shared residential corridors, laundry rooms, fitness center and lounge, plus ground floor retail. The case study tables in this chapter compare the proposed building envelope features to Mandatory and Prescriptive Energy Code requirements and evaluate possible compliance options.

Figure 15: Mid-Rise Multifamily: North and West View

Figure 16: Mid-Rise Multifamily: South and East View

Table 11-17: Mid-Rise Multifamily Case Study Compared to Mandatory and Prescriptive Envelope Requirements (Climate Zone 12)

Total Conditioned Floor Area and Fenestration

Source: California Energy Commission

Figure 17: Section 100.0(f) Exception 1 for Mixed Occupancy

Table 11-18: Fenestration Case Studies Types and Locations

1st Floor: Mixed Occupancy: Retail (Nonresidential) and Multifamily Common Use

Storefront Fixed, Swinging Doors: NFRC-Rated dual pane low-e glass, thermal break metal frame

2nd-5th Floors: Multifamily Dwelling Units and Multifamily Common Use

Horizontal Sliders, Sliding Glass Doors, Fixed Sidelites: Manufactured NFRC-rated, Architectural Window (AW) Performance Grade, dual pane, low-e glass, vinyl frame

Source: California Energy Commission

Table 11-19: Roof, Wall, and Floor, plus Verifications Case Studies
Roof and Ceiling: Insulation, Radiant Barrier and Roofing

Wall Insulation (Note: Mandatory maximum U-factors must be met for Performance compliance options.)

Floor Insulation

Figure 18: Mid-Rise Multifamily: 5th Floor, 2-Bedroom Apartment, Plan View with North and East Elevations

This case study is a mixed occupancy building with 85.6 percent multifamily dwelling units and common use areas and 14.4 percent nonresidential retail spaces. According to Energy Code Section 100.0(f) Exception 1, if one occupancy in a mixed use building is at least 80 percent of total conditioned floor area, the whole building has the option of complying with the Prescriptive requirements of the dominant occupancy. Note that each separate occupancy type still has to comply with its own lighting requirements and mandatory requirements.

For this case study, the whole building envelope could either meet multifamily prescriptive requirements, or the nonresidential and multifamily areas could comply separately. Based on the results shown in the comparison table, it probably makes sense to show compliance separately for the retail and multifamily areas in this case study. All of the case study envelope features at least meet Mandatory U-value requirements, except for the uninsulated concrete walls on the west side of the first floor and at the stairwells.

There is no alternative to meeting Mandatory requirements, even for performance method compliance. Those concrete walls will have to have a maximum U-factor of 0.690 instead of the proposed U-factor of 0.740 for the project overall to comply at all.

The table also shows several design features that meet mandatory requirements, but do not comply prescriptively. If even one measure misses the prescriptive requirements, the overall project fails prescriptive compliance. In that situation, the project owners and design team would need to make changes to the design to show prescriptive compliance or else work with an energy analyst to evaluate the building using the performance approach to find trade-offs between different building features. Note that the Performance Approach usually works best when modeling the building envelope together with other building components such as the mechanical and water heating systems, since that may allow more opportunities for trade-offs.

Figure 19: NFRC Label (Units) AW Rating & NFRC certificate (Storefront)

Source: California Statewide CASE team

Figure 20: 1st : 8" Concrete Wall (2022 Ref. App. Fig. 4.3.6)

Figure 21: Metal Framed Wall

Figure 22: 1 Hour Fire-Rated R-21 Wood Framed Wall

Figure 23: 5th: Wood Frame Rafter Roof (2022 Ref. App. Fig. 4.2.2)

Figure 24: 2nd and 4th: Deck Roofs (2022 Ref. App. Fig. 4.2.2)

Figure 25: 4th: Raised Floor (2022 Ref. App. Fig. 4.4.2)

On a different note, this case study highlights that there are separate Prescriptive multifamily fenestration U-factor, RSHGC and visible transmittance (VT) requirements for products certified to meet the North American Fenestration Standard/Specification (NAFS) for an Architectural Windows (AW). AW performance grade windows are designed to withstand high wind loads or other physical loads, and for this study the design team determined that they were needed for all of the dwelling units to address a very windy site location. AW performance grade fenestration is generally seen in high-rise and mid-rise buildings. U-factor, RSHGC and VT values for AW performance grade fenestration still need to be determined through NFRC rating or other methods defined in Energy Code Section 110.6.