3.4 Opaque Envelope

This section of the building envelope chapter addresses the requirements for air leakage, roof products, radiant barriers, and vapor retarders in the building envelope. Fenestration, windows, glazed doors, and opaque doors are addressed in Section 3.3. Insulation is addressed in Section 3.5.

Table 3-5: Relevant Sections in the Energy Standards

Newly Constructed and Additions

> 1,000 ft2




Air Leakage




Roofing and Radiant Barriers

§10-113, §110.8(i) - §110.8(j)

§150.1(c)2, §150.1(c)11

Table 150.1-A

§150.1(a), §150.1(b)

Vapor Retarders




3.4.1    Opaque Envelope Definitions

Opaque elements of the building envelope significantly contribute to the related energy efficiency. Components of the building envelope include walls, floors, soffits, roofs, and ceilings. Envelope and other building components definitions are listed in §100.1(b) of the Energy Standards and the Reference Appendices JA1.

A.   The exterior partition is an opaque, translucent, or transparent solid barrier that separates conditioned space from ambient air or unconditioned space.

B.   The demising partition is a wall, fenestration, floor, or ceiling that separates conditioned space from enclosed unconditioned space.

C.   The conditioned space is an enclosed space within a building that is either directly conditioned or indirectly conditioned.

D.   Unconditioned space is enclosed space within a building that is neither directly conditioned nor indirectly conditioned.

E.   Plenum is an air compartment or chamber, including uninhabited crawl space, areas above a ceiling or below a floor, or attic spaces, to which one or more ducts are connected and that forms part of either the supply-air, return-air, or exhaust air system, other than the occupied space being conditioned.

F.   Attic is an enclosed space directly below the roof deck and above the ceiling.

G.   Sloping surfaces are considered either a wall or a roof, depending on the slope. (See Figure 3-9.) If the surface has a slope of less than 60° from horizontal, it is considered a roof; a slope of 60° or more is a wall. This definition extends to fenestration products, including windows in walls and any skylight types in roofs.


Figure 3-9: Slope of a Wall or Window (Roof or Skylight Slope Is Less Than 60°)


Source: California Energy Commission


H.   The exterior roof is an exterior partition that has a slope less than 60 degrees from horizontal, that has conditioned space below, and that is not an exterior door or skylight.

I.    The roof deck is the surface that supports the roofing material. Typically made of plywood or OSB, it is, in turn, supported by the roof framing members such as rafters or trusses.

J.   Exterior floor/soffit is a horizontal exterior partition, or a horizontal demising partition, under conditioned space.

K.   Vapor retarder or vapor barrier is a material or assembly designed to limit the amount of vapor moisture that passes through that material or assembly.

L.   Roofing products are the top layer of the roof that is exposed to the outside, which has properties including, but not limited to, solar reflectance, thermal emittance, and mass.

M.  Cool roof is a roofing material with high thermal emittance and high solar reflectance, or low thermal emittance and exceptionally high solar reflectance, as specified in Part 6, that reduces heat gain through the roof.

N.   Solar reflectance is the fraction of solar energy that is reflected by the roof surface.

O.   Thermal emittance is the fraction of thermal energy that is emitted from the roof surface.

P.   A low-sloped roof is a surface with a pitch less than 2:12 (less than 9.5 degrees from the horizon).

Q.   A steep-sloped roof is a surface with a pitch greater than or equal to 2:12 (9.5 degrees or greater from the horizontal).

R.   Air leakage (AL) is a measurement of heat loss and gain by infiltration through gaps and cracks in the envelope.


Infiltration is the unintentional replacement of conditioned air with unconditioned air through leaks or cracks in the building envelope. It is a major component of heating and cooling loads. Infiltration can occur through holes and cracks in the building envelope and around doors and fenestration framing areas.

Reducing infiltration in the building envelope can result in significant energy savings, especially in climates with severe winter and summer conditions. It also can result in improved occupant comfort, reduced moisture intrusion, and fewer air pollutants.

Exfiltration is uncontrolled outward air leakage from inside a building, including leakage through cracks, joints, and intersections, around windows and doors, and through any other exterior partition or duct penetration.

S.   Ventilation is the intentional replacement of conditioned air with unconditioned air through open windows and skylights or mechanical systems.

3.4.2    Air Sealing and Air Leakage §110.7, §150.0    Joints and Other Openings §110.7


Figure 3-10: Air Sealing



Source: Sierra Building Science


Air leakage through joints, penetrations, cracks, holes, openings around windows, doors, walls, roofs, and floors can result in higher energy use. The following openings in the building envelope shall be caulked, gasketed, weatherstripped, or otherwise sealed:

1.  Exterior joints around window and door frames (including doors between the house and garage), between interior HVAC closets and conditioned space, between attic access and conditioned space, between wall sill plates and the floor, exterior panels, and all siding materials.

2.  Openings for plumbing, electricity, and gas lines in exterior and interior walls, ceilings, and floors.

3.  Openings in the attic floor, such as where ceiling panels meet interior walls, exterior walls, and masonry fireplaces.

4.  Openings around exhaust ducts, such as those for clothes dryers.

5.  All other such openings in the building envelope.


Source: California Energy Commission


Alternative strategies may be used to meet the mandatory caulking and sealing requirements for exterior walls.

These include, but are not limited to: 

1.  Stucco.

2.  Caulking and taping all joints between wall components (for example, between slats in wood slat walls).

3.  Building wraps.

4.  Rigid wall insulation installed continuously on the exterior of the building with all joints taped, gasketed, or otherwise sealed.    Fireplaces, Decorative Gas Appliances, and Gas Logs §150.0(e)

The Energy Standards have mandatory requirements to limit infiltration associated with fireplaces, decorative gas appliances, and gas logs. Reduced infiltration is a benefit when the fireplace is not operating (the majority of the time for most homes).

3.4.3       Roofing Products §10-113, §110.8(i), §150.1(c)11

In general, light-colored, high-reflectance surfaces reflect solar energy (visible light and invisible infrared and ultraviolet radiation) and stay cooler than darker surfaces that absorb the sun’s energy and become heated. The Energy Standards prescribe cool roof radiative properties for low-sloped and steep-sloped roofs. Low-sloped roofs receive more solar radiation than steep-sloped roofs in the summer when the sun is higher in the sky.

Roofing products installed to take compliance credit or meet the prescriptive requirements for reflectance and emittance shall be rated by the Cool Roof Rating Council (CRRC) and labeled appropriately by the roofing manufacturer for solar reflectance and thermal emittance. The solar reflectance and thermal emittance properties are rated and listed by the Cool Roof Rating Council at (www.coolroofs.org/).    Product Labels §10-113

Figure 3-12 shows a sample Cool Roof Rating Council product label. The label includes solar reflectance and thermal emittance values.

Figure 3-12: Sample CRRC Product Label and Information

Source: Cool Roof Rating Council

Solar reflectance and thermal emittance are measured from 0 to 1; the higher the value, the "cooler" the roof. There are numerous roofing materials in a wide range of colors that have adequate cool roof properties. Reducing heat gains through the roof will reduce the cooling load of the home, resulting in reduced air-conditioned energy needed to maintain occupant comfort. High-emitting roof surfaces reject absorbed heat quickly (upward and out of the building) than roof surfaces with low-emitting properties. 

Solar Reflectance (SR).  There are three solar reflectance measurements:

1.  Initial solar reflectance

2.  Three-year aged solar reflectance

3.  Accelerated aged solar reflectance

All requirements of the Energy Standards are based on the three-year aged solar reflectance. If the aged SR value is not available in the CRRC’s Rated Product Directory, then the aged value shall be derived from the CRRC aged value equation (using the initial value for solar reflectance) or an accelerated process. Until the appropriate aged-rated value for the reflectance is posted in the directory, the equation below can be used to calculate the aged rated solar reflectance or a new method of testing is used to find the accelerated solar reflectance.

Calculating Aged Solar Reflectance From Initial Reflectance

Equation 3-1:   Aged Reflectancecalculated=(0.2+ β[ρinitial – 0.2])


ρinitial = Initial Reflectance listed in the CRRC Rated Product Directory

β = soiling resistance which is listed in Table 3-6


Table 3-6: Values of Soiling Resistance β by Product Type



Field-applied coating




Thermal Emittance (TE). The Energy Standards do not distinguish between initial and aged thermal emittance, meaning either value can be used to demonstrate compliance with the Energy Standards.


What is Solar Reflectance Index (SRI)?

An alternative to the aged solar reflectance and thermal emittance required values is to use the Solar Reflectance Index (SRI) to show compliance. A calculator has been produced to calculate the SRI by inputting the three-year aged solar reflectance and thermal emittance of the desired roofing material.

The calculator can be found at http://www.energy.ca.gov/title24/2019standards.

By using the SRI alternative, a cool roof may comply with a lower emittance, as long as the aged reflectance is higher, and vice versa.


Example 3-14: ENERGY STAR® Roofing Products


Question: I am a salesperson who represents several roofing products. Many of them are on the ENERGY STAR® list published by the U.S. Environmental Protection Agency (EPA) for cool roofing materials. Is this sufficient to meet the Energy Standards?


Answer: No. ENERGY STAR has different requirements than the Energy Standards for reflectance and no requirements for emittance. Per §10-113, the Cool Roof Rating Council (www.coolroofs.org) is the only entity recognized by the California Energy Commission to determine what qualifies as a cool roof.


Example 3-15: Certifying Products With the Cool Roof Rating Council (CRRC)


Question: How does a product get CRRC cool roof certification?

Answer: CRRC publishes its certification procedures in the CRRC-1 Program Manual, available for free at www.coolroofs.org or by calling CRRC at (866) 465-2523 (toll free within the USA) or (510)-485-7176.  Anyone new to the certification process and wishing to have one or more products certified should contact CRRC by phone or by email at info@coolroofs.org. Working with CRRC is strongly recommended; staff walks interested parties through the procedures.


Example 3-16: Reflectance vs. Emittance


Question: I understand reflectance, but what is emittance?


Answer: Material that reflects the sun’s energy will still absorb some of that energy as heat; there are no perfectly reflecting materials being used for roofing. The absorbed heat is given off (emitted) to the environment in varying amounts depending on the materials and surface types. This emittance is given a value between 0 and 1, and this value represents a comparison (ratio) between what a given material or surface emits and what a perfect blackbody emitter would emit at the same temperature.

A higher emittance value means more energy is released from the material or surface; scientists refer to this emitted energy as thermal radiation. Emittance is a measure of the relative efficiency with which a material, surface, or body can cool itself by radiation. Lower-emitting materials become relatively hotter due to holding in heat. Roof materials with low emittance hold onto more solar energy as heat, and that held heat can be given off downward into the building. More heat in the building increases the need for air conditioning for comfort. A cool roof system that reflects solar radiation (has high reflectance) and emits thermal radiation well (has high emittance) will result in a cooler roof and a cooler building with lower air-conditioning costs.    Mandatory Requirements

Field-Applied Liquid Coatings §110.8(i)4

There are several liquid products, including elastomeric coatings and white acrylic coatings, that qualify for field-applied liquid coatings. The Energy Standards specify minimum performance and durability requirements for field-applied liquid coatings. These requirements do not apply to industrial coatings that are factory-applied, such as metal roof panels. The requirements address elongation, tensile strength, permeance (rate of water vapor transmission), and accelerated weathering. The requirements depend on the type of coating and are described here in greater detail. Liquid roof coatings applied to low-sloped roofs in the field as the top surface of a roof covering shall comply with the following mandatory requirements and descriptions.

Aluminum-Pigmented Asphalt Roof Coatings. Aluminum-pigmented coatings are silver-colored coatings that are commonly applied to modified bitumen and other roofing products. The coating has aluminum pigments that float to the surface of the coating while it is setting, providing a shiny and reflective surface. Because of the shiny surface and the physical properties of aluminum, these coatings have a thermal emittance below 0.75, which is the minimum rating for prescriptive compliance.

This class of field-applied liquid coatings shall be applied across the entire surface of the roof and meet the dry mil thickness or coverage recommended by the manufacturer, depending on the substrate on which the coating will be applied. The aluminum-pigmented asphalt roof coatings shall be manufactured in accordance with ASTM D2824. Standard specification is also required for aluminum-pigmented asphalt roof coatings, nonfibered, asbestos-fibered, and fibered without asbestos that are suitable for application to roofing or masonry surfaces by brush or spray, and installed in accordance with ASTM D3805, Standard Guide for Application of Aluminum-Pigmented Asphalt Roof Coatings.

Cement-Based Roof Coatings. This class of coatings consists of a layer of cement that may be applied to almost any type of roofing. Cement-based coatings shall be applied across the entire roof surface to meet the dry mil thickness or coverage recommended by the manufacturer. Cement-based coatings shall be manufactured to contain no less than 20 percent Portland cement and meet the requirements of ASTM D822, ASTM C1583, and ASTM D5870.

Other Field-Applied Liquid Coatings. Other field-applied liquid coatings include elastomeric and acrylic-based coatings. These coatings must be applied across the entire roof surface to meet the dry mil thickness or coverage recommended by the manufacturer, depending on the substrate on which the coating will be applied. The field-applied liquid coatings must be tested to meet several performance and durability requirements as specified in Table 110.8-C of the Energy Standards or the minimum performance requirements of ASTM C836, D3468, or D6694, whichever are appropriate to the coating material.    Prescriptive Requirements §150.1(c)11

Steep-sloped and low-sloped energy-efficient cool roofs are prescriptively required in some climate zones. The prescriptive requirement is based on an aged solar reflectance and thermal emittance tested value from the Cool Roof Rating Council (CRRC). If a cool roof is being installed to comply with the Energy Standards, it must meet mandatory product and labeling requirements.


Table 3-7: Prescriptive Cool Roof Requirements

Prescriptive Cool Roof Requirements

Solar Reflectance and Thermal Emittance Values


Roof Type

Climate Zone

Minimum Three-Year Solar Reflectance

Minimum Thermal Emittance

Minimum SRI


10 through 15





13 and 15





There are two exceptions to meeting these prescriptive requirements:

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


2.  Roof constructions that have a weight of at least 25 lb/ft².

The project could choose to pursue the performance approach and trade off the prescriptive cool roof requirements. See Section 3.6 and Chapter 8 for more on the performance approach.    Compliance and Enforcement 

The plans examiner should ensure that the solar reflectance and thermal emittance values documented on the CF1R-ENV-04 are specified on the building plans at the time of permit application.

The inspector can verify that the values on the CRRC label for the installed roof product meet or exceed the solar reflectance and thermal emittance values on the CF1R compliance document.


If a manufacturer does not obtain a 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 SR and 0.75 TE

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

3.4.4    Radiant Barriers §110.8(j), §150.1(c)2    Mandatory Requirements §110.8(j)


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 http://www.bearhfti.ca.gov/industry/thermal_insulation.shtml.    Prescriptive Requirements §150.1(c)2, RA4.2.1

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 only require a radiant barrier in Climate Zones 2, 3, and 5 through 7. The radiant barrier is a reflective material that reduces radiant heat transfer into the attic caused by solar heat gain in the roof.

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 Residential Reference Appendices 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 3-13 for drawings of radiant barrier installation methods.

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


Figure 3-13: Methods of Installation for Radiant Barriers

Source: California Energy Commission


Radiant Barriers in the 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. See more in Section 3.6 and Chapter 8.

3.4.5    Vapor Retarder §150.0(g) and RA4.5.1

When is a vapor retarder required?

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 climates 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.    Product Requirements

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

There are many product types having tested vapor retarder performance. Some common examples include the following:

1.  Foil and other facings on gypsum board can provide moisture resistance, and product literature should always be checked to ensure conformance to ASTM E96. 

2.  The kraft paper used as 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. See Figure 3-14.

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 3-14: Typical Kraft-Faced Vapor Retarder Facing

Description: 3ber_vapor-barr-kraft-ppr_r1