3.3 Fenestration (Window/Skylight/Glazed Door) and Opaque Doors

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 a home. The size, orientation, and types of fenestration products can dramatically affect the overall energy performance of a house. Glazing type, orientation, shading, and shading devices not only play a major role in the energy use of a building, but can affect the operation of the lighting system, HVAC system, and comfort of occupants.


Table 3-1: Relevant Sections in the Energy Standards





Fenestration and Opaque Doors

§10-111, §10-112, §110.6, §150.0(q), Tables 110.6-A for U-factors and Table 110.6-B

§150.1(c)3, §150.1(c)4, §150.1(c)5

Table 150.1-A and Table 150.1-B

§150.1(a), §150.1(b)

Limit Air Leakage




3.3.1    Fenestration Types    Windows and Glazed Doors

A window is a vertical fenestration product that is an assembled unit consisting of a frame and sash component holding one or more pieces of glazing. Window performance is measured with the U-factor and solar heat gain coefficient (SHGC).

Glazed doors are an exterior door having a glazed area of 25 percent or more of the area of the door. Glazed doors are treated the same as windows and must meet the U-factor and SHGC requirements for windows. Most sliding glass doors, French doors, and some entry doors with large amounts of glazing will meet the definition to be treated as glazed doors.    Opaque Doors

When the door has less than 25 percent glazing material, it is considered an opaque door and is subject to the door U-factor requirements. Doors between the garage and conditioned space that are required to have fire protection are not required to meet the U-factor requirement.    Skylights and Tubular Daylight Devices

Skylights and tubular daylight devices (TDD) are an exceptional source of daylight and passive solar heating, illuminating rooms with direct and indirect sunlight. When used appropriately, daylighting can increase the quality of light in a room and reduce dependence upon electrical lighting.

Skylights and TDDs don’t typically have the same thermal properties as vertical fenestration and can be prone to greater heat loss in winter and solar heat gain during the summer. When a building designer optimizes the whole envelope glazing arrangement for daylight and thermal control, significant heating and cooling energy savings can be realized, especially when skylights and TDDs are as efficient as other vertical windows used.

Windows are considered part of an exterior wall when the slope is 60° or more as measured from the horizontal. Where the slope of fenestration is less than 60°, the glazing indicated as a window is considered a skylight and part of the roof.    Fenestration Subcategories

A.   Manufactured fenestration is a fenestration product constructed of materials that are factory-cut or otherwise factory-formed with the specific intention of being used to fabricate a fenestration product. Knocked down or partially assembled products may be sold as a fenestration product when provided with temporary and permanent labels, as described in §10-111, or as a site-built fenestration product when not provided with temporary and permanent labels, as described in §10-111.

B.   Site-built fenestration is designed to be field-glazed or field-assembled units, using specific factory-cut or other factory-formed framing, and glazing units that are manufactured with the intention of being assembled at the construction site. These include storefront systems, curtain walls or large-track sliding glass walls, and atrium roof systems.

C.   Field-fabricated fenestration is when the windows are fabricated at the building site from elements that are not sold together as a fenestration product (that is, separate glazing, framing, and weatherstripping elements). Field-fabricated does not include site-assembled frame components that were manufactured elsewhere with the intention of being assembled on site (such as knocked-down products, sunspace kits, and curtain walls).    Fenestration Definitions

A.   Center of glass. U-factor, SHGC, and VT are measured only through glass at least 2.5 inches from the edge of the glass or dividers.

B.   Clear glass has little, if any, observable tint with an IG unit with an SHGC of 0.5 or greater.

C.   Chromogenic is a class of glazing that can change the optical properties by including active materials (e.g. electrochromic) and passive materials (e.g. photochromic and thermochromic) permanently integrated into the glazing assembly.

Electrochromatic is a class of glazing that tints on demand using a small amount of electricity.

D.   Divider (muntin). An element that physically or visually divides different lites of glass. It may be a true divided lite, between the panes, and/or applied to the exterior or interior of the glazing.

E.   Double-pane window. Double-pane (or dual-pane) glazing is made of two panes of glass (or other glazing material) separated by space (generally 1/4" [6 mm] to 3/4" [18 mm]) filled with air or other gas. Two panes of glazing laminated together do not constitute double-pane glazing

F.   Dynamic glazing. Glazing systems that have the ability to reversibly change the performance properties, including U-factor, solar heat gain coefficient (SHGC), and/or visible transmittance (VT) between well-defined end points. Includes active materials (for example, electrochromic) and passive materials (for example, photochromic and thermochromic) permanently integrated into the glazing assembly.

With appropriate controls, electrochromic glass can be darkened or lightened to adjust the levels of daylight and solar heat gain. These products have the ability to reversibly change the SHGC and VT between well-defined endpoints.

Integrated shading systems is a class of fenestration products including an active layer (for example, shades, louvers, blinds, or other materials) permanently integrated between two or more glazing layers and that has the ability to reversibly change performance properties, including U-factor, SHGC, and/or VT between well-defined end points.

G.   Fixed. The fenestration product cannot be opened.

H.   Gap width. The distance between glazing in multiglazed systems (e.g., double or triple glazing). This dimension is measured from inside surface to inside surface. Some manufacturers may report "overall" IG unit thickness, which is measured from outside surface to outside surface.

I.    Grille. See Divider.

J.   Insulating glass unit (IG unit or IG). An IG unit includes the glazing, coatings, tinting, spacer(s), films (if any), gas infills, and edge caulking.

K.   Light or lite. A layer of glazing material, especially in a multilayered IG unit. Referred to as panes in §110.6 when the lites are separated by a spacer from inside to outside of the fenestration.

L.   Low-e coatings. Low-emissivity coatings are special coatings applied to the second, third, or fourth surfaces in double-glazed windows or skylights. As the name implies, the surface has a low emittance, meaning that radiation from that surface to the surface it “looks at” is reduced. Since radiation transfer from the hot side to the cool side of the window is a major component of heat transfer in glazing, low-e coatings are very effective in reducing the U-factor. They do nothing, however, to reduce losses through the frame.

Low-e coatings can be engineered to have different levels of solar heat gain. Generally, there are two kinds of low-e coatings:

1.   Low-solar-gain low-e coatings are formulated to reduce air-conditioning loads. Fenestration products with low-solar-gain low-e coatings typically have an SHGC of 0.40 or less. Low-solar-gain low-e coatings are sometimes called spectrally selective coatings because they filter much of the infrared and ultraviolet portions of the sun’s radiation while allowing visible light to pass through.

2.   High-solar-gain low-e coatings, by contrast, are formulated to maximize solar gains. Such coatings would be preferable in passive solar applications or where there is little air conditioning.

Another advantage of low-e coatings, especially low-solar-gain low-e coatings, is that when they filter the sun’s energy, they generally remove between 80 percent and 85 percent of the ultraviolet light that would otherwise pass through the window and damage fabrics and other interior furnishings. This is a major advantage for homeowners and can be a selling point for builders.

M.  Mullion. A frame member that is used to join two windows into one fenestration unit.

N.   Muntin. See Dividers.

O.   Nonmetal frame. Includes vinyl, wood, fiberglass, and other low-conductance materials. Vinyl is a polyvinyl chloride (PVC) compound used for frame and divider elements with a significantly lower conductivity than metal and a similar conductivity to wood. Fiberglass has similar thermal characteristics. Nonmetal frames may have metal strengthening bars entirely inside the frame extrusions or metal-cladding only on the surface.

P.   Operable. The fenestration product can be opened for ventilation.

Q.   Solar heat gain coefficient (SHGC). A measure of the relative amount of heat gain from sunlight that passes through a fenestration product. SHGC is a number between zero and one that represents the ratio of solar heat that passes through the fenestration product to the total solar heat that is incident on the outside of the window. A low SHGC number (closer to 0) means that the fenestration product keeps out most solar heat. A higher SHGC number (closer to 1) means that the fenestration product lets in most of the solar heat.

SHGC or SHGCt is the SHGC for the total fenestration product and is the value used for compliance with the standards.

R.   Spacer or gap space. A material that separates multiple panes of glass in an insulating glass unit.

S.   Thermal break frame. Includes metal frames that are not solid metal from the inside to the outside but are separated in the middle by a material with a significantly lower conductivity.

T.   Tinted. Glazing products formulated to have the appearance of color that alters the solar heat gain and visible transmittance. Common colors include gray, bronze, green, and blue. Some coatings can also appear tinted.

U.   U-factor. A measure of how much heat can pass through a construction assembly or a fenestration product. The lower the U-factor, the more energy efficient the product is. The units for U-factor are British thermal units (Btu) of heat loss each hour per square foot (ft²) of window area per degree Fahrenheit (°F) of temperature difference (Btu/hr-ft²-°F). U-factor is the inverse of R-value.

The U-factor considers the entire product, including losses through the center of glass, at the edge of glass where a metal spacer typically separates the double-glazing panes, losses through the frame, and through the mullions. For metal-framed fenestration products, the frame losses can be significant.

V.   Visible transmittance (VT) is the ratio of visible light transmitted through the fenestration. The higher the VT rating, the more light is allowed through a window.

W.  Window films are composed of a polyester substrate to which a special scratch-resistant coating is applied on one side, with a mounting adhesive layer and protective release liner applied to the other side.

3.3.2    Mandatory Requirements §10-111, §10-112, §110.6    Fenestration Products and Labeling §10-111; §110.6(a)5

The National Fenestration Rating Council (NFRC) is the entity recognized by the California Energy Commission to supervise the rating and labeling of fenestration products. NFRC maintains the Certified Product Directory, containing NFRC certified U-factors, SHGC and VT values for thousands of fenestration products, on its website at http://www.nfrc.org. 

Fenestration product performance data used in compliance calculations must be provided through the NFRC rating program and must be labeled by the manufacturer with the rated U-factor, SHGC, and VT in accordance with §10-111 procedures.

Estimating the rate of heat transfer through a fenestration product is complicated by the variety of frame configurations for operable windows, the different combinations of materials used for sashes and frames, and the difference in sizes available in various applications. The NFRC rating system makes the differences uniform, so that an entire fenestration product line is assumed to have only one typical size. The NFRC-rated U-factor may be obtained from the directory of certified fenestration products, directly from a manufacturer's listing in product literature, or from the product label.

U-factor and solar heat gain (SHGC) are factors that affect the energy performance of a window. There is no minimum requirement for visual transmittance (VT) for low-rise residential buildings but is used for informational purposes. Product labels that clearly state these energy performance ratings help consumers compare the energy efficiency of window and glazed door products of different brands and manufacturers.

There are two types of labels that may be used to meet the requirements in the Energy Standards: an NFRC-certified product label or a default label. Manufactured products will need to have both an NFRC temporary label listing certified performance values and a permanent label with information that can be used to trace the product certification file and show that the manufacturer has certified the product per one of the testing methods described in Table 3-2. See the “Certified Product Labels” section for more information. Default U-factors and SHGC are used when the manufacturer has not certified the product through the NFRC and for site-built fenestration. The temporary default label shall meet the requirements per §10-111. See the “Default Label” section for more information.    Certified Product Labels: Temporary and Permanent

1.   Temporary Label for NFRC Certified Manufactured Fenestration Products
The Energy Standards require that manufactured fenestration have both temporary and permanent labels. The temporary label shows the U-factor and SHGC for each rated window unit. The label must also show that the product meets the air infiltration criteria of §110.6(a). The temporary label must not be removed before inspection by the enforcement agency.


Figure 3-2: Sample Temporary NFRC Label


Source: National Fenestration Rating Council

2.   National Fenestration Rating Council (NFRC) Permanent Label
The permanent label must, at a minimum, identify the certifying organization and have an ID number or code to allow tracking back to the original information on file with the certifying organization, NFRC. The permanent label can also be inscribed on the spacer, etched on the glass, engraved on the frame, or otherwise located so as not to affect aesthetics.    Default Label: Temporary

The manufacturer can choose to use Energy Standards default values from Table 110.6-A for U-factors and Table 110.6-B for SHGC. The product shall meet the air infiltration requirements of §110.6(a)1, U-factor criteria of §110.6(a)2, and SHGC criteria of §110.6(a)3 in the Energy Standards. The manufacturer must attach a temporary label meeting the following specific requirements. (Permanent etching labels are not required.)

There is no template for the default temporary label. It must be clearly visible and large enough for the enforcement agency field inspectors to read easily. It must include all information required by the Energy Standards. The minimum suggested label size is 4 in. x 4 in., and the label must have the following words at the bottom of the label as noted in Figure 3-3:

“Product meets the air infiltration requirements of §110.6(a)1, U-factor criteria of §110.6(a)2, SHGC criteria of §110.6(a)3 and VT criteria of §110.6(a)4 of the 2019 California Building Energy Efficiency Standards for Residential and Nonresidential Buildings.”

The manufacturer ensures the U-factor and SHGC default values are large enough to be readable from four feet away. The manufacturer ensures the appropriate boxes are checked and indicated on the default label.


Figure 3-3: Sample of Default Temporary Label

2019 California Energy Commission Default Label

XYZ Manufacturing Co.

Key Features:

o Doors

o Double-Pane

o Skylight

o Glass Block




Frame Type

Product Type:

Product Glazing Type:

o Metal

o Operable

o Clear

o Non-Metal

o Fixed

o Tinted

o Metal, Thermal Break

o Greenhouse/Garden    Window

o Single-Pane

o Air space 7/16 in. or      greater

o With built-in curb

o Meets Thermal-Break Default Criteria


To calculate VT see NA6

California Energy Commission

Default U-factor =

California Energy Commission

Default SHGC =

California Energy Commission

Calculated VT =

Product meets the air infiltration requirements of §110.6(a)1, U-factor criteria of §110.6(a)2, SHGC criteria of §110.6(a)3 and VT criteria of §110.6(a)4 of the 2019 Building Energy Efficiency Standards  for Residential and Nonresidential Buildings.

Source: California Energy Commission


At the field inspection, the field inspector verifies that the fenestration U-factor and SHGC values meet the energy compliance values by checking the label sticker on the product. If no labels are available on site for verification, the field inspector should not allow any further installation of fenestration until proof of efficiency (label) is produced. In cases when proof is not met, the field inspector should not allow construction until the designer or builder can produce such labels.

Manufactured Products. Product must be rated by the National Fenestration Rating Council (NFRC) and be listed in NFRC’s Certified Product Directory (CPD). The test procedure for U-factor is NFRC 100, and for SHGC and VT is NFRC 200 and NFRC 202, or ASTM E972 for translucent panels, and NFRC 203 for tubular daylighting devices (TDDs) and for certain types of other skylights.

Energy Commission Default Tables 110.6-A and 110.6-B in the Energy Standards list the worst-case values that must be assumed in most cases when fenestration is not rated by NFRC. For example, a single-pane, operable, metal-framed fenestration product has a default U-factor of 1.28. To get credit for high-performance window features such as low-emissivity (low-e) coatings and thermal break frames, the window manufacturer must have the window tested, labeled, and certified according to NFRC procedures. When the Energy Standards default values are used, they must be documented on a temporary default label (Figure 3-3).

Site-Built Products. For special cases in low-rise residential construction in which site-built products are installed, the site-built products shall be treated the same as manufactured products. U-factor and SHGC values must come from NFRC ratings or from the default Table 110.6-A and 110.6-B of the Energy Standards. Alternatively, calculation procedures in Reference Appendix NA6 for nonrated site-built fenestration may be used if the area of the site-built fenestration in a dwelling is less than 250 ft2 or 5 percent of the conditioned floor area, whichever is larger.

Field-Fabricated Products. Field-fabricated fenestration must always use the Energy Commission default U-factors from Table 110.6-A and SHGC values from Table 110.6-B of the Energy Standards.


Example 3-1: Labels When Using CEC Default Values

Question: When windows are labeled with a default value, are there any special requirements that apply to the label?

Answer: All windows must meet the mandatory requirements in §110.6 and §110.7, unless exempted.  These criteria apply to fenestration products labeled with default values:

The administrative regulations (§10-111) require that the words “CEC Default U-factor” and “CEC Default SHGC” appear on the temporary label before the U-factor or SHGC (not in a footnote).

The U-factor and SHGC for the specific product must be listed. If multiple values are listed on the label, the manufacturer must identify the appropriate value for the labeled product. Marking the correct value must be done in one of the following ways:

1. Circle the correct U-factor and SHGC (permanent ink).

2. Black out all values except the correct U-factor and SHGC (permanent ink).

3. Make a hole punch next to the appropriate values.

3.3.3    U-Factor and SHGC Ratings §110.6(a), Table 110.6-A, Table 110.6-B

Determining U-Factor and SHGC. The Energy Standards require that U-factor and solar heat gain coefficient (SHGC) be calculated using standardized procedures to ensure that the thermal performance or efficiency data for fenestration products is accurate. The data provided by different manufacturers within each fenestration type (windows, doors, skylights, TDDs) can easily be compared to others within that type and can be verified independently.

Acceptable methods of determining U-factor and SHGC are shown in Table 3-2.


Table 3-2: Methods for Determining U-Factor and SHGC

Determination Method

Manufactured Windows and Doors

Manufactured Skylights

Site-Built Fenestration (Vertical &

Field-Fabricated Fenestration


NFRC-100 (U-Factor)







Standards Default

Table 110.6-A (U-Factor)

Table 110.6-B (SHGC)






NFRC’s Component Modeling Approach (CMA)1












1.  The NFRC CMA method is limited to nonresidential and is not currently approved for residential use.

2.  The Alternative Default U-factors and SHGCs from Reference Appendix NA6 may be used only for total site-built vertical fenestration plus skylights up to 250 ft2 or 5% of the conditioned floor area, whichever is larger. Residential area allowances are defined in NA6.1(b).



When the alternative procedure from NA6 for unrated site-built fenestration is used in a residential application, it may not meet the prescriptive values as required by Table 150.1-A, even if area-weighted averaging is implemented. In this case, it would be necessary to use the performance approach to meet energy complianc


Example 3-2: Multiple Window Types in a Project

Question: My new home will have a combination of window types, including fixed, operable, wood, metal, and so forth, some of which are field-fabricated. What are the options for showing compliance with the standards?

Answer: All windows must meet the mandatory requirements of §110.6 and §110.7 and the mandatory maximum area-weighted average U-factor of 0.58 from §150.0(q), unless exempted. For field-fabricated windows, you must select U-factors and SHGC values from the default tables (Table 110.6-A and Table 110.6-B of the Energy Standards). Windows that are not field-fabricated must be labeled with NFRC-certified or default efficiencies. Few fenestration products in the default tables meet the mandatory maximum U-factor of 0.58 on their own. 

If the area-weighted average U-factors or SHGC values do not comply with the prescriptive requirements, the performance method must be used. To simplify data entry into the compliance software, you may choose the U-factor from Table 110.6-A of the Energy Standards that is the highest of any of the windows planned to be installed and use this for all windows for compliance. However, you must use the appropriate SHGC from Table 110.6-B for each window type being installed.


Example 3-3: Glass Block

Question 1: Which U-factor is used for an operable metal-framed glass block?

Answer 1: For glass block, use the U-factor from Table 110.6-A of the Energy Standards for the frame type in which the glass blocks are installed and for the fenestration product type. The U-factor for operable metal-framed glass block from Table 110.6-A is 0.87.

Question 2: Which SHGC is used for clear glass block, and can it be used for tinted glass block?

Answer 2: Use the default SHGC values from Table 110.6-B, depending upon whether the glass block has a metal or nonmetal frame and whether it is operable or fixed. The default SHGC table does not include tinted glass block, so use the clear glass block SHGC as the default for both clear and tinted glass block.

Question 3: Does it need a label? 

Answer 3: Glass block is considered a field-fabricated product and may be installed only if compliance is demonstrated on the compliance documents.


Example 3-4: Sunrooms

Question: Is there a default U-factor for the glass in sunrooms?

Answer: If the sunroom is part of the conditioned floor area, then yes. For the horizontal or sloped portions of the sunroom glazing, use the U-factor for skylights. For the vertical portions, use the U-factors for fixed windows, operable windows, or doors, as appropriate. As a simple alternative, the manufacturer may label the entire sunroom with the highest U-factor of any of the fenestration types within the assembly.


Example 3-5: Glazed Doors

Question 1: How are exterior glazed doors treated in compliance documentation for U-factor and SHGC?

Answer 1: All doors with glass area greater than or equal to 25 percent of the door area, which includes French doors, are defined as fenestration products and are covered by the NFRC Rating and Certification Program. The U-factor and SHGC for doors with 25 percent or more glass area may be determined in one of two ways:

1. Use the NFRC rated and labeled values.

2. Refer to Table 110.6-A and 110.6-B of the Energy Standards. The values are based upon glazing and framing type.

In special cases where site-built fenestration is being installed in a residential application, the site-built windows and glazed doors can use an alternative method to calculate the U-factor and the SHGC by using the manufacturer’s center-of-glass values (COG). The COG values are calculated in accordance with Reference Appendix NA6. To use this calculation, the maximum allowed site-built fenestration is 250 ft2 or 5% of the conditioned floor area, whichever is larger.

Question 2: How can I determine a U-factor and SHGC for doors when less than 25 percent of the door area is glass?

Answer 2: Doors with less than 25 percent glass area are treated as opaque exterior doors. For prescriptive or performance approaches, only the U-factor is used for this product type. Use one of the following options for U-factor of the door:

1. The NFRC label if one is available

2. The default values from Table JA4.5.1 of the Reference Appendices


Example 3-6: Tubular Daylighting Device With Single-Pane Diffuser

Question: A tubular daylighting device will be used to get daylight into a house. The skylight has a clear plastic dome exterior to the roof, a single-pane ¼-inch (6 mm)-thick acrylic diffuser mounted at the ceiling, and a metal tube connecting the two. How are U-factor and SHGC determined for the performance approach to comply with the Energy Standards, if Uc is 1.20 and SHGCc is 0.85?

Description: 3ber_tubular-skylights_r1

Answer: There are three methods available for determining the U-factor for tubular daylighting devices (TDD):

1. Use the NFRC label if the product has been tested and certified under NFRC procedures. This requires a label that states: “Manufacturer stipulates that this rating was determined in accordance with applicable NFRC procedures NFRC 100,” followed by the U-factor.

2. Use the default U-factor from Table 110.6-A of the Energy Standards. This tubular product would be considered a metal frame, fixed, single-pane skylight resulting in a U-factor of 1.19, which must appear on a label preceded by the words “CEC Default U-factor.” (A tubular daylighting device would have to have two panes of glazing with an air space of less than 2 inches [50 mm] between them at the plane of the ceiling insulation for it to be considered double-pane.)

3. Determine the U-factor from Reference Appendix NA6, Equation NA6-1. The U-factor for this tubular daylighting device would be based on metal with no curb (Table NA6-5). The U-factor for this skylight, using Equation NA6-1, is 1.25, where Ut = (0.195 + (0.882 x 1.20)). This must appear on a label stated as “CEC Default U-factor 1.25.”

There also are three methods available for determining SHGC for tubular daylighting devices (TDD): 

1. Use the NFRC label if the skylight has been tested and certified under NFRC procedures and requires a label that states: “Manufacturer stipulates that this rating was determined in accordance with applicable NFRC procedures.”

2. Use the default table SHGC in Table 110.6-B of the Energy Standards. This tubular daylight device would be considered a metal-frame, fixed, clear, single-pane skylight resulting in an SHGC of 0.83, which must appear on a label stated as “CEC Default SHGC 0.83.”

3. Determine the SHGC from Reference Appendix NA6, Equation NA6-2. The SHGC for this skylight using Equation NA6-2 is 0.81, where SHGCt = (0.08 + (0.86 x 0.85)). This must appear on a label stated as “CEC Default SHGC 0.81.”


Example 3-7: Tubular Daylighting Device With Dual-Pane Diffuser

Question: How are the U-factor and the SHGC determined if the tubular daylighting device in the previous example has a dual-pane diffuser (instead of single-pane) mounted at the ceiling?

Answer: The procedure would be exactly the same as Example 3-6, except that the double-pane U-factor and SHGC values from Tables 110.6-A and 110.6-B of the Energy Standards would be used instead of single-pane values. Up to 3 ft2 of tubular daylighting device with a dual-pane diffuser is assumed to have the prescriptive U-factor and SHGC from Table 150.1-A or Table 150.1-B for compliance calculations (Exception 1 to §150.1[c]3A).

3.3.4    Air Leakage §110.6(a)1, §110.7

Air leakage (AL) is a measurement of heat loss and gain by infiltration through cracks in the window assembly, which can affect occupant comfort. The lower the AL, the lower the amount of air that will pass through cracks in the window assembly. 

A.   Manufactured Products. Must be tested and certified to leak no more than 0.3 cubic feet per minute (cfm) per ft² of the window area. This mandatory measure applies to all manufactured windows that are installed in newly constructed residential (including high-rise) buildings or newly installed in existing buildings. To determine leakage, the standard test procedure requires manufacturers to use either NFRC 400 or ASTM E283 at a pressure differential of 75 Pascal (or 1.57 pounds/ft2).

B.   Site-Built Products. There are no specific air leakage requirements for site-built fenestration products, but the Energy Standards require limiting air leakage by weatherstripping and caulking.

C.   Field-Fabricated Products. No air leakage testing is required for field-fabricated fenestration products; however, the Energy Standards still require limiting air leakage by weatherstripping and caulking.

D.   Exterior Doors. Exterior doors, which includes pet doors, must meet the following requirements:

1.  Manufactured exterior doors must be certified as meeting an air leakage rate of 0.3 cfm/ft² of door area at a pressure differential of 75 Pascal, which is the same as windows.

2.  Field-fabricated exterior doors must comply with the requirements of §110.6, as described by “Other Openings.” For example, these must be caulked and weatherstripped.

3.  Any door with a surface area greater than or equal to 25 percent glass is considered a glazed door and must comply with the mandatory and applicable prescriptive and performance requirements of §150.0, §150.1(b), and §§150.2.

4.  For any door with a surface area less than 25 percent glass, the area may be exempt in accordance with one of the exceptions of §150.0, §150.1(b), and §150.2.


Example 3-8: Which Fenestration Products Must Be Tested and Certified for Air Leakage?

Question: As a manufacturer of fenestration products, I place a temporary label with the air infiltration rates on my products. Can you clarify which products must be tested and certified?

Answer: Each product line must be tested and certified for air infiltration rates. Features such as weather seal, frame design, operator type, and direction of operation affect air leakage. Every product must have a temporary label certifying that the air infiltration requirements are met. This temporary label may be combined with the temporary U-factor, SHGC, and VT label.


Example 3-9: Infiltration Requirements for Custom Windows

Question: Is a custom window “field-fabricated” for meeting air infiltration requirements?

Answer: No. Most custom windows are manufactured and delivered to the site either completely assembled or “knocked down,” which means they are a manufactured product. A window is considered field-fabricated when the windows are assembled at the building site from the various elements that are not sold together as a fenestration product (such as glazing, framing, and weatherstripping). Field-fabricated does not include site-assembled frame components that were manufactured elsewhere with the intention of being assembled on site (such as knocked-down products, sunspace kits, and curtain walls).

Example 3-10: Pet Doors to the Exterior

Question: How is a pet door installed in an exterior wall accounted for in a newly constructed residential building design?

Answer: Pet doors must meet all exterior door requirements. U-factor must be determined by an NFRC accredited testing lab using NFRC 100 U-factor requirements; otherwise, nonrated pet doors will assume no more than the maximum U-factor of 0.99 based on a nonmetal single-pane door U-factor. (See Table 110.6-A of the Energy Standards.) The rated pet door shall not exceed 0.3 cfm/ft² air leakage when tested using ASTM E283. The performance compliance approach must be used when a pet door is installed.

3.3.5    Prescriptive Requirements §150.1(c)3, §150.1(c)4, §150.1(c)5, Table 150.1-A and Table 150.1-B


Prescriptive requirements described in this chapter typically refer to Table 150.1-A or 150.1-B. The maximum fenestration U-factor required prescriptively for all climate zones is 0.30, and the maximum SHGC is 0.23 for residences in Climate Zones 2, 4, and 6 through 15. Homes constructed in Climate Zones 1, 3, 5, and 16 have no SHGC requirements.

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 SHGC of windows, glazed doors, and skylights can be area weight-averaged together to meet the prescriptive requirement using the CF1R-ENV-02-E compliance document in Appendix A of this manual.

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 considered a glazed door and is treated like a fenestration product (Section 3.5.8).

Opaque doors are prescriptively required to have an area-weighted average U-factor no greater than U-0.20, per Table 150.1-A and Table 150.1-B. Swinging doors between the garage and conditioned space that are required to have fire protection are exempt from the prescriptive requirement. The U-factor must be rated in accordance with NFRC 100, or the applicable default U-factor defined in Reference Appendix 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 (Figure 3-3).


Table 3-3: Maximum U-Factors, SHGC, and Fenestration Area by Climate Zone
in the Prescriptive Package

Climate Zone

1, 3, 5, 16


Maximum Fenestration U-Factor



Maximum Fenestration SHGC



Maximum Fenestration Area



Maximum West-Facing Fenestration Area



Maximum Opaque Door U-Factor



Figure 3-4: Prescriptive Package, SHGC, and West-Facing Area Criteria by Climate Zone    Fenestration and Opaque Door Prescriptive and Mandatory Exceptions

A.   Glazed Doors

Any door that is more than 25 percent or greater glass is considered a glazed door and must comply with the mandatory measures and other requirements applicable to a fenestration product. Up to 3 ft2 of glass in a door is exempt from the U-factor and SHGC requirements (or can be considered equivalent to the prescriptive package values). The U-factor and SHGC shall be based on either the NFRC values for the entire door, including glass area, or use default values in Table 110.6-A for the U-factor and Table 110.6-B for the SGHC. If the door has less than 25 percent glazing, the opaque part of the door is ignored in the prescriptive approach.

B.   Tubular Daylighting Device (TDD)
In each dwelling unit, up to 3 ft2 of tubular daylighting devices area with dual-pane diffusers at the ceiling are exempt from the prescriptive U-factor and SHGC requirements, where the TDD area is included in the maximum of 20 percent fenestration area. However, the U-factor shall not exceed a maximum of 0.58. See §150.0(q) and Exception 1 of §150.1(c)3A.

C.   Opaque Doors

Opaque doors between the garage and conditioned space that are required to have fire protection are not required to meet the prescriptive U-factor requirement of 0.20. See Exception to §150.1(c)5.

D.   Skylights

Each new dwelling unit may have up to 16 ft2 of skylight area. The total area of skylights is included in the maximum of 20 percent fenestration area and must meet a maximum 0.55 U-factor and a maximum SHGC of 0.30. See Exception 2 of §150.1(c)3A.

Aside from the specific exceptions to the fenestration prescriptive requirements, the area weight-averaged U-factor and SHGC must not exceed the 0.55 U-factor and cannot be greater than the 0.30 SHGC when large numbers of skylights are used for prescriptive compliance. Alternatively, the performance approach may be used to meet energy compliance.

E.   Dynamic Glazing
If a dwelling unit includes a type of dynamic glazing that is electrochromatic, chromogenic, or an integrated shading device and the glazing is automatically controlled, use the lowest U-factor and lowest SHGC to determine compliance with prescriptive package fenestration requirements. Since this type of product has compliance ratings that vary, it cannot be weight averaged with nonchromogenic products as per Exception 3 of §150.1(c)3A.

F.   Site-Built Fenestration
When a dwelling unit contains a combination of manufactured and site-built fenestration, only the site-built fenestration values can be determined by using Reference Appendix NA6. All fenestration, including site-built, can default to Table 110.6-A and Table 110.6-B.

G.   Maximum Area
The prescriptive requirements limit total glass area to a maximum of 20 percent of the conditioned floor area in all climate zones.

Note: There are exceptions to the prescriptive requirements for alterations in §150.2(b)1A that allow additional glass area beyond the 20 percent limitation, including west-facing glass. See Chapter 9 for more information on alterations.

H.   Greenhouse Windows/Garden Windows

Compared to other fenestration products, the NFRC-rated U-factor for greenhouse windows are comparatively high. Section §150.0(q) includes an exception from the U-factor requirement for dual-glazed greenhouse or garden windows that total up to 30 ft² of fenestration area.    Prescriptive Credit for Exterior Shading Devices §150.1(c)4

The prescriptive requirements require fenestration products with a SHGC of 0.23 or lower in Climate Zones 2, 4, and 6 through 15. However, a fenestration product with an SHGC greater than 0.23 may be used with the prescriptive requirements if a qualifying exterior shading device is used and the combined area-weighted average complies with the prescriptive requirements. Exterior shading devices and associated SHGC values are shown in Table 3-4. These include woven sunscreens as well as perforated metal sunscreens. As shown in the table, these devices transmit between 13 percent and 30 percent of the sun that strikes them.


Table 3-4: Exterior Shades and Solar Heat Gain Coefficients

Exterior Shading Device


Standard Bug (insect) Screen (default for windows)


Exterior Sunscreens With Weave 53 x 16/inch    


Louvered Sunscreens w/Louvers as Wide as Window Openings


Low-Sun-Angle Louvered Sunscreen


Vertical Roller Shades or Retractable/Drop Arm/ Combination/Marquisolette and Operable Awnings


Roll Down Blinds or Slats


None (for skylights only)


* Reference glass values assume single-pane clear glass and metal framing 1/8-inch double-strength (DSS) glass. Use CF1R-ENV-03 worksheet for calculation.


When exterior overhangs are used, the SHGC requirements of the prescriptive package may be met if the calculated combination of the overhang and fenestration SHGC efficiency is equal or lower than 0.23.

For credit, exterior shading devices must be permanently attached as opposed to being attached using clips, hooks, latches, snaps, or ties. Exterior shading devices on windows or skylights that are prohibited by life-safety codes from being permanently attached for emergency egress reasons are exempt from this requirement.


Compliance document CF1R-ENV-03 is used to calculate the combined SHGC of windows and exterior shading devices. When exterior shades are required for compliance, they must be listed on the CF1R and be documented on the plans.


The SHGC of the window in combination with an exterior device is given by the following:

Equation 3-1

SHGCcombined = (0.2875 x SHGCmax + 0.75) x SHGCmin

All operable windows and skylights are assumed to have an insect screen as the default condition against which other window and exterior shading device combinations are compared. The standard case is a window with an SHGC of 0.23 and an insect screen with an SHGC of 0.76. For this default case, the SHGC of the window is the SHGCmin, and the SHGC of the exterior sunscreen is SHGCmax. Working through the math on the CF1R-ENV-03 form, SHGCcombined is 0.23. This means that any combination of window SHGC and exterior SHGC that results in a SHGCcombined of 0.23 or less complies with the prescriptive requirements.

Most of the shading devices (other than the default insect screen) have an SHGC of 0.30 or lower. Combining this with the SHGC of any window may result in a combined SHGC that is equal to or lower than the prescriptive criterion of 0.23. This method of combining the SHGC of the window with the SHGC of the exterior shading device can also be used in the whole-building performance approach.

3.3.6    Fenestration in the Performance Approach §150.1(b)

While the prescriptive requirements and mandatory measures establish a minimum level of building energy performance, opportunities to exceed the requirements of the Energy Standards are considerable. More information is included in the Performance Compliance section (Chapter 8).


Options that are recognized for credit through the performance method are called compliance options. Most require using the performance approach, but a few exterior shading devices and south-facing overhangs may be used to comply when using the prescriptive approach.    Fenestration Area and Orientation

The performance approach includes consideration of the fenestration area and orientation, which can have a big effect on energy use. Compliance is determined by comparing the proposed fenestration to the standard design fenestration.

For buildings with glazing areas less than or equal to 20 percent of the conditioned floor area (CFA), the standard design fenestration for new construction is modeled with the same glazing area as the proposed home with one-quarter of the window area on the north, east, south, and west orientations. For buildings with more than 20 percent of the CFA, the standard design is limited to 20 percent glass area.

Because of the effects of orientation and the fenestration product performance levels and other building features like overhangs, judging the particular area, orientation, and performance level is a compliance credit or penalty and can be difficult to determine without performance approach calculations.    Improved Fenestration Performance

The fenestration weighted average U-factor in the standard design for newly constructed buildings is 0.30 in all climate zones, as indicated in the single-family and multifamily prescriptive packages. Choosing high-performance fenestration that performs better than the prescriptive requirements level can earn significant credit through the performance method. For example, in air-conditioning climates, choosing a window with an SHGC lower than 0.23 will reduce the cooling loads compared to the standard design.

The magnitude of the effect will vary by climate zone. In mild coastal climates, the benefit from reducing fenestration U-factor will be smaller than in cold, mountain climates. Several factors affect window performance. For fenestration with NFRC ratings, the following performance features are accounted for in the U-factor and SHGC ratings:

1.   Frame materials, design, and configuration (including cross-sectional characteristics). Fenestration can be framed in many materials. The most common include wood, aluminum, vinyl, fiberglass, 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.

2.   Number of panes of glazing, low-emissivity 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 coating and argon gas fill with an improved spacer. The choice of low-emissivity 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. There are many ways to improve performance beyond the prescriptive levels. Adding glazing layers such as triple glazing and low-emissivity coatings such as those facing the conditioned space are two likely improvements.

3.   Dynamic glazing with appropriate controls may also offer opportunities for improving performance.    Fixed Permanent Shading Devices

Shading of windows is also an important compliance option. Overhangs or sidefins that are attached to the building or shading from the building itself are compliance options for which credit is offered through the performance approach. However, no credit is offered for shading from trees, adjacent buildings, or terrain.

The ideal overhang is one that provides shade during the months when the building is likely to be in cooling mode and allows direct solar gains in the heating months. During the summer, the sun is high as it passes over the south side, while in the winter it is low, enabling solar radiation to pass beneath the overhang. Windows that face south can be effectively shaded by overhangs positioned above the window. Due to the potential effectiveness of south-facing overhangs, a prescriptive compliance option is offered. See Section for details.

Shading is more challenging on the east and west sides of the house. When the sun strikes these façades, it is fairly low in the sky, making overhangs ineffective. Vertical fins can be effective, but they degrade the quality of the view from the window and limit the natural light that can enter. In cooling-dominated climates, the best approach is to minimize windows that face east and west. Landscaping features can be considered to increase comfort and energy performance of the building but cannot be used for compliance credit.    Interior Shading Devices

Figure 3-5: Diagram of Integrated Shading System

Source: NFRC Dynamic Glazing Productes Fact Sheet

There is no credit for interior aftermarket shading devices, although they can be effective in reducing solar gains and should

be considered by homeowners. These added interior shades are in the category of home furnishings and not a feature of the house that is provided by the builder or fenestration manufacturer. Draperies, interior blinds, interior shades, and other interior devices are not credited toward energy compliance. A default standard bug screen is still considered in performance calculations, so that estimates of energy use are more realistic and tradeoffs against other measures are more equitable.    Dynamic Glazing

Dynamic glazing products are either integrated shading systems or electrochromatic devices and are considered a fenestration product.

Integrated Shading Systems. These systems include blinds positioned between glass panes that can be opened and closed using automatic controls.

The labels for integrated shading systems will reflect the endpoints of the product performance for U-factor and SHGC (Figure 3-6). The unique rating “variable arrow” identifier helps consumers understand the “dynamics” of the product and allows comparison with other similar dynamic fenestration products.

If the fenestration product can operate at intermediate states, a dual directional arrow (↔) with the word “Variable” will appear on the label. Some dynamic glazing is able to adjust to intermediate states, allowing for a performance level between the endpoints.


In Figure 3-6, the low value rating is displayed to the left (in the closed or darker position), and the high value rating is displayed to the right (in the open or lighter position). This lets the consumer know at a glance the best and worst case performance of the product and the default performance level. To use the high-performance values for integrated shading systems, the product must have an NFRC Certified Label sticker. Otherwise, the default values from Tables 110.6-A and Table 110.6-B must be used.

Chromatic Glazing. One type of dynamic glazing product uses a chromatic type of glass that has the ability to change the performance properties, allowing occupants to control their environment manually or automatically by tinting or darkening a glass with the flip of a switch. Some fenestration products can change performance automatically with the use of an automatic control or environmental signals. These high-performance windows can reduce energy costs due to controlled daylighting and unwanted heat gain or heat loss.


Figure 3-7: Chromatic Glazing

Source: Sage Electrochromics

A view of chromatic glazing in the open (off) and closed (on) position is shown in Figure 3-7. Best-rated performance values may be used for compliance with an NFRC Certified Label sticker and when automatic controls are installed.

If the window includes either an NFRC label or automatic controls, but not both, then default to Table 150.1-A maximum U-factor of 0.30 and maximum SHGC of 0.23.

If neither an NFRC label nor automatic controls are included, then the default values from Tables 110.6-A and  110.6-B of the Energy Standards must be used.    Window Films §150.1(b)

Window films are polyester films that offer high clarity and can be pretreated to accept different types of coatings. There are three basic categories of window films:

Clear (nonreflective) films are used as security film to reduce ultraviolet (UV) light, which contributes greatly to fading. They are not commonly used for solar control or energy savings.

Tinted or dyed (nonreflective) films reduce both heat and light transmission, mostly through increased absorbance, and can be used in applications where the desired primary benefit is glare control, with energy savings being secondary.

Metalized (reflective) film can be metalized through vacuum coating, sputtering, or reactive deposition and may be clear or colored. Metalized films are preferred for energy savings applications because they reduce transmission primarily through reflectance and are manufactured to reflect heat more than visible light through various combinations of metals.

To receive window film compliance credit, the following must be met:

      The performance approach must be used to meet energy compliance.

      NFRC Window Film Energy Performance Label (Figure 3-8) is required for each different film applied. If there is no NFRC label, the default values from Tables 110.6-A and Table 110.6-B of the Energy Standards must be used.

      Window films must have at least a 15-year manufacturer warranty.

Figure 3-8 shows an example of a NFRC Attachment Ratings Label, which helps identify the energy performance of window films.    Bay Windows §150.1(b)

Bay windows are a special compliance case. Bay windows may have a unit NFRC rating (that is, the rating covers both the window and all opaque areas of the bay window), an NFRC rating for the window only, or no NFRC rating. Nonrated bay windows may or may not have factory-installed insulation.

A.   NFRC Rated
For bay windows that come with an NFRC rating for the entire unit, compliance is determined based on the rough opening area of the entire unit, applying the NFRC U-factor and SHGC. If the unit U-factor and SHGC do not meet the package requirements or area-weighted average, the project must show compliance using the performance approach.

B.   Nonrated
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.

      Opaque portions of bay windows including roofs and floors must be insulated to meet the wall insulation requirements for prescriptive compliance. The opaque portion must either meet the minimum insulation requirements of the prescriptive package for the applicable climate zone or be included in a weighted average U-factor calculation of an overall opaque assembly that does meet the prescriptive requirements.

      For the windows, the U-factor and SHGC values may be determined either from an NFRC rating or by using default values in Tables 110.6-A and 110.6-B of the Energy Standards. If the window U-factor and SHGC meet the package requirements, the bay window complies prescriptively (if overall building fenestration area meets prescriptive compliance requirements).

      If the bay window does not meet prescriptive requirements, the project must show compliance using the performance approach.