3.5       Fenestration    

Windows, glazed doors, dynamic glazing, window films, and skylights have a significant impact on energy use in a home. Fenestration accounts for a large impact on heating and cooling loads of residential and high-rise residential space conditioning loads, 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 building’s energy use, but can affect the load operation of the HVAC system and the comfort of occupants.

3.5.1    Fenestration Types

When choosing a new or replacement window, it’s always best to look for a National Fenestration Rating Council (NFRC) rated label sticker on the window. The Energy Performance Ratings label is designed to help consumers identify a rating, or a measurement scale that is reflective of a window's energy performance. This will help the consumer or designer to compare the energy efficiency of window and glazed door products, per different brands and manufacturers as well.

The following NFRC label sticker provides information about the energy performance rating by listing identifiers; U-factors, Solar Heat Gain Coefficient (SHGC), Visible Transmittance (VT), and Air Leakage (AL) which helps provide accurate information for the consumer or designer. The label references the following information:

1.   U-factor measures the rate of heat loss through a product. Therefore, the lower the U-factor, the lower the amount of heat loss.  In cold climates where heating bills are a concern, choosing products with lower U-factors will reduce the amount of heat that escapes from inside the house.

2.   The Solar Heat Gain Coefficient (SHGC) measures the percentage of heat in radiant heat that passes through a fenestration product. Therefore, the lower the SHGC, the less amount of solar heat gain. In hot climates where air conditioning bills are a concern, choosing products with a lower SHGC will reduce the amount of heat that comes in from the outside.

3.   Visible Transmittance (VT) measures the percent amount of light that comes through a fenestration product. The higher the VT rating, the more light is allowed through a window or glazed door. Skylight’s significantly allows more lighting and can be as efficient as vertical windows.

4.   Air Leakage (AL) is a measurement of heat loss and gain by infiltration through cracks in the window assembly and it affects the occupant comfort. The lower the AL, the less air will pass through cracks in the window assembly. 

There are three primary categories of fenestration:

A.   WINDOWS

A window is fenestration including skylights that is an assembled unit consisting of a frame and sash component holding one or more pieces of glazing. New advances in framing material such as composites, fiberglass and vinyl help improve the energy efficiency of all fenestration products. New technology has advanced the glass industry to include reflective coatings such as silver, gold, bronze, low-e, low-e², or low-e³ which can be applied to clear and tinted glass. 

The following is a list of sub-categories of fenestration;

A.   Manufactured Fenestration is a fenestration product constructed of materials which 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 Section 10-111; or as a site-built fenestration product when not provided with temporary and permanent labels as described in Section 10-111.

B.   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 (i.e., glazing, framing and weather stripping). 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).

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

D.   system that has the ability to reversibly change its performance properties, including U-factor, Solar Heat Gain Coefficient (SHGC), and Visible Transmittance (VT) between well-defined end points.  These may Dynamic Glazing is a glazing include, but are not limited to chromogenic glazing systems and integrated shading systems.  Dynamic Glazing systems may include internally mounted or externally mounted shading devices that attach to the window framing/glazing that may or may not be removable, but only if they are part of the original window, door or skylight assembly and the assembly is labeled as such.

E.   Windows Films Window Films were originally developed in the early 1950’s, and are mostly made of polyester substrate that is durable, tough and highly flexible. It absorbs little moisture and has both high arid and low temperature resistances. Polyester film offers crystal clarity and can be pre-treated to accept different types of coatings for energy control and long term performance. Window films are made with a special scratch resistant coating on one side and with a mounting adhesive layer on the other side. The adhesive is normally applied to the interior surface (room side) of the glass, unless it is a film specifically designed for the exterior window surface. 

B.   GLAZED DOORS

Glazed door is an exterior door having a glazed area of 50 percent or more of the area of the door. These doors are typically installed in exterior walls that separate conditioned space from exterior ambient or unconditioned space. When the door is less than 50 percent it will no longer be considered a glazed door but is a door.  The glass area will still have to be counted towards the overall glass area of the conditioned space.

C.   SKYLIGHTS

Skylights are an exceptional source of daylight and passive solar heating, illuminating rooms with direct and indirect sunlight.  In 'addition, when used appropriately, daylighting can increase the quality of room light and reduce dependence upon electrical lighting.  On the other hand, skylights 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 window designer optimizes the whole envelope glazing arrangement for good daylight and thermal control, significant heating and cooling energy savings can be realized, especially when skylights with the same technology as efficient vertical windows are used.

3.5.2    Relevant Sections in the Standards for Fenestration     

A.   §10-111 (Administrative Standards) establishes the rules for rating and labeling fenestration products and establishes the NFRC as the supervising authority.

B.   §110.6(a)1 sets air leakage requirements for all manufactured windows, doors and skylights whether they are used in residential or nonresidential buildings.

C.   §110.6(a)2 through 4 requires that the U-factor, solar heat gain coefficient (SHGC), and visible transmittance (VT)  for manufactured fenestration products be determined using NFRC procedures or use default values.

D.   §110.6(a)5 requires that manufactured fenestration products have both a temporary and permanent label. The temporary label shall show the U-factor, SHGC and the VT and verify that the window complies with the air leakage requirements.

E.   §110.6(b) field-fabricated fenestration that do not have an NFRC rating shall use the CEC default U-factors, SHGC and optional VT values.

F.   §110.7 requires that openings around windows, skylights and doors be caulked, gasketed, weatherstripped or otherwise sealed to limit air leakage.

G.   §150.0(q) requires a mandatory U-factor of 0.58 or a maximum weighted average U-factor of 0.58 for windows and skylights separating conditioned space from unconditioned space or the outdoors. An exception allows the greater of 10 ft² or 0.5% of the conditioned floor area to exceed 0.58 U-factor.

H.   §150.1(c)3 and 4 meet the prescriptive requirements for fenestration and shading in low-rise residential buildings. These include requirements for maximum glazing area, maximum U-factor, and for some climate zones, a maximum SHGC requirement.

I.    §150.1(c)3A, in 'addition to be basic fenestration allowance of 20% of CFA, Exception 1 allows each dwelling unit to have up to 3 ft² of glazing installed in doors and up to 3 ft² of tubular daylighting device with dual-pane diffusers to have an assumed U-factor and SHGC equivalent to the Package requirements.

J.   §150.1(c)3A, in 'addition to be basic fenestration allowance of 20% of CFA, Exception 2 allows up to 16 ft² of the skylights to have up to 0.55 U-factor and up to 0.30 SHGC in each dwelling.

K.   §150.1(c)3A Exception 3 allows automatically controlled chromogenic glazing (a type of dynamic glazing) to assume the lowest U-factor and SHGC when connected to automatically controls that modulate the amount of heat flow into space in multiple steps in response to solar intensity, chromogenic glazing shall be considered separately from other fenestration, and must be not be weight averaged with other fenestration.

L.   §150.1(c)3A Exception 4 specifies that if a residential dwelling unit contains a combination of manufactured and site-built fenestration; only the site-built fenestration can be determined by using Nonresidential Reference Appendix NA6; however, all fenestration and including sit-built can also default to TABLES 110.6-Aor B.

M.  §150.1(c)3B establishes a prescriptive limit that the prescriptive maximum total fenestration area shall not exceed the percentage of conditioned floor area (CFA) indicated in TABLE 150.1-A. Total fenestration includes skylights and west-facing glazing.

N.   §150.1(c)3C states that when west-facing glazing is limited by Package A, west-facing includes skylights tilted in any direction when the pitch is less than 1:12.

O.   §150.2(a) sets the prescriptive fenestration area requirements for residential additions as well as other prescriptive requirements for new windows. Performance compliance options (existing plus addition) are also available.

P.   §150.2(b) establishes the prescriptive requirements for replacement windows in existing residences. Performance compliance options (existing plus alteration) are also available.

3.5.3    Mandatory Measures, Feature and Devices

A.   Air Leakage.  Manufactured fenestration products, including exterior doors, 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 newly installed in residential, high-residential or existing buildings. To determine leakage, the standard test procedure requires manufacturers to use is 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 Standards require limiting air leakage through weatherstripping and caulking.

"Note In the case when unrated NFRC site-built fenestration is used in a residential application there is an alternative procedure to calculate the default thermal efficiencies U-factor and SHGC values of such products. Using this alternative may not result in meeting the prescriptive values as listed in Table 150.1-A.  However, it may be used in the Performance Approach. The alternative calculation can be found in the Reference Nonresidential Appendices NA6."

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

D.   Exterior Doors. Exterior 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.   Exterior doors must comply with the requirements of §110.7, as described in “Joints and Other Openings,” e.g., they must be caulked and weatherstripped if field-fabricated.

3.   Any door whose surface area has greater than 50 percent glass is considered as a glazed door and must comply with the Mandatory and applicable Prescriptive and Performance requirements of §150.0, §150.1, and §150.2. 

Alternatively, if less than 50 percent of glass the area may be exempt in accordance with one of the exceptions of §150.0, §150.1, and §150.2. 

3.5.4    U-factor and SHGC Rating Mandatory Requirements    

Requiring that U-factor and SHGC be calculated using a standardize procedure ensures that the thermal performance or efficiency data for fenestration products are accurate and the data provided by different manufacturers within each fenestration type (windows, doors, skylights, TDDs) can be easily compared to others within that type and can be independently verified.

For manufactured fenestration products, the mandatory requirements are that the U-factor and Solar Heat Gain Coefficient (SHGC) be rated by NFRC and be listed in NFRC’s Certified Product Directory (CPD). The test procedure for U-factor is NFRC 100, and for SHGC is NFRC 200 and NFRC-200, NRC-202 or ASTM E972 for translucent panels and NFRC-203 for tubular daylighting devices skylights (TDDs), and for certain type of skylights.

At the time of field inspection, the field inspector verifies the fenestration U-factor and SHGC values meets the energy compliance values by checking the NFRC label sticker on the window.

Alternatively, 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. See Sample Default Label Figure 3-2.

Note: If no labels are available on site for verification, the field inspector should cease any further installation of fenestration until proof of efficiency (label) is produced on site or filed in the field office. In cases when proof is not met then the field inspector can cease construction until the architect/ specifier can produce such labels.

The Energy Commissions default U-factors are listed in TABLE 110.6-A, and the default SHGC values are listed in TABLE 110.6-B(also in Appendix B of this compliance 'manual).

Note: While there is no minimum VT value requirement for residential compliance, the value may be shown on the temporary label for information only. A listing of NFRC certified ratings is available at www.NFRC.org.

Energy Commission (CEC) default values in TABLE 110.6-A and TABLE 110.6-B in the Standards list the worst possible values that can be assumed when fenestration is not rated by NFRC. To get credit for high performance window features such as low-e (low-emissivity) coatings and thermal break frames, the window manufacturer must have the window tested, labeled, and certified according to NFRC procedures.

A.   Site-built Fenestration Products. For low-rise residential construction, site-built products are treated the same as manufactured products: proof of U-factor and SHGC values must come from NFRC ratings or from Standards default TABLE 110.6-A and TABLE 110.6-B.

Note: When only unrated site-built fenestration is used in a residential application there is an alternative procedure to calculate the default U-factor and SHGC values. Though using this alternative may not result in meeting the prescriptive values as required by Table 150.1-A. The alternative calculation can be found in the Reference Nonresidential Appendices NA6 or it may require to use the performance approach to meet energy compliance.

B.   Field-fabricated Products §110.6(b). Field-fabricated fenestration must always use the Energy Commission default U-factors from Standards TABLE 110.6-A and SHGC values from TABLE 110.6-B. There is no minimum requirement for VT, but only used for informational purposes.

For acceptable methods of determining U-factor and SHGC are shown in Table 3-1A and Table 3-1B respectively.

Table 3-1A – Acceptable Methods for Determining U-factor

Table 3-1B – Methods for Determining Solar Heat Gain Coefficients

3.5.5    Labeling Mandatory Requirements

A.      Default Temporary Label

The manufacturer can also choose to use Energy Commission (CEC) default values from TABLE 110.6-A for U-factors and TABLE 110.6-B  for SHGC. If default values are used, the manufacturer must attach a temporary label meeting the following specific requirements (permanent etching labels are not required). 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 Building Energy Efficiency Standards for Residential and Nonresidential Buildings.

Although there is no exact format for the default temporary label, it must be clearly visible and large enough for the enforcement agency field inspectors to read easily and it must include all information required by the 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 3-2;

“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 2013 California Building Energy Efficiency Standards for Residential and Nonresidential Buildings.”

The manufacturer ensures the U-factor and SHGC default values should be large enough to be visible from 4 feet away. The manufacturer ensures the appropriate checkboxes are checked and indicated on default label.

3.5.6    Certified Temporary and Permanent Labels

A.   Certified Manufactured Fenestration Products
The Standards require that manufactured fenestration have both temporary and permanent labels. The temporary label shows the U-factor and SHGC, on for each rated window. The label must also show that the window meets the air infiltration criteria. The temporary label must not be removed before inspection by the enforcement agency.

B.   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 also can be inscribed on the spacer, etched on the glass, engraved on the frame, or otherwise located so as not to affect aesthetics.

C. Field-Fabricated Fenestration A label is not required for field-fabricated fenestration products, but the CEC default values in TABLE 110.6-A and TABLE 110.6-B from the Standards must be used and documented on the Fenestration Certificate NRCC-ENV-05-E (formerly FC-1) form.

3.5.6 

3.5.7    Fenestration U-factor

With the 2013 update, the mandatory maximum U-factor is set by §150.0(q) for fenestration including skylights to be at maximum U-factor of 0.58. While there is an allowance for area-weighted averaging, this will limit the use of single pane products. Up to 10 ft² or 0.5% of conditioned floor area (whichever is greater) is exempt from the maximum U-factor requirement.

Table 3-3 – Maximum U-factors, SHGC and Fenestration Area by Climate Zone in Packages A

Figure 3-4 – Package A SHGC Criteria by Climate Zone

3.5.8    Prescriptive Requirements    

Prescriptive requirements described in this chapter typically refer to Package A or Table 150.1-A of the Standards. The maximum U-factor required by prescriptive Package A for all climate zones is 0.32 and the maximum Solar Heat Gain Coefficient (SHGC) is 0.25 or lower for dwellings in climate zones 2, 4, and 6-16. Homes constructed in climate zones 1, 3, and 5 have no maximum 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 WS-2R form in Appendix A of this 'manual.

3.5.9    Fenestration Prescriptive Exceptions    

A.   Doors and Tubular Daylighting Device

In each dwelling unit, up to 3 ft² of the glazing area installed in doors and 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 area is included in the maximum of 20 percent fenestration area.  However, the U-factor shall not exceed a maximum is 0.58. See §150.0(q) and Exception 1 of §150.1(c)3A.

B.   Skylights

Each new dwelling unit may have up to 16 ft² of skylight area; the area is included in the maximum of 20 percent fenestration area and meets 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, U-factors and SHGCs for skylights can be significantly higher than they are for windows so long as their area weight-averaged U-factor and SHGC do not exceed the 0.55 U-factor and is not greater than the 0.30 SHGC when large amounts of individual skylights are used for  prescriptive compliance. Alternatively, the performance approach should be used for meeting energy compliance.

C.   Dynamic Glazing

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

D.   Site-Built Fenestration

When residential dwelling unit contains combination of manufactured and site-built fenestration; only site-built fenestration values can be determined by using Nonresidential Reference Appendix NA6; however, all fenestration and including sit-built can default to TABLES 110.6-A or B.

E.   Window Maximum Area

The prescriptive requirements limit total glass area to a maximum of 20 percent of the conditioned floor area in all climate zones, however there are exceptions to the prescriptive requirements for alterations in §150.2(b)1A which allow additional glass area beyond the 20 percent limitation, including west-facing glass.

Figure 3-5 – Package A, Prescriptive West-Facing Window Area Limits by Climate Zone

F.   Shading

While a low emissivity (low-e) coating on the glass is one of the most common ways to reduce solar gain in combination with insulated window frame, there are other options to help increase shading:

•      Use of permanent installed exterior shade screens;

•      Louvers on the outside of the window are typically used on windows facing south. See Table 3-4 for different types of Exterior Shades and Solar Heat Gain Coefficients;

Properly sized overhang - See Fixed Permanent Shading Devices discussed later in this chapter below.

G.   Dynamic Glazing:

Dynamic Glazing products are either Integrated Shading Systems or Electro-Chromatic type devices and are considered a fenestration product.  Integrated shading systems include blinds positioned between glass panes that can be opened and closed manually or using automatic controls. The labels for internal shading systems will reflect the endpoints of the product’s performance for U-factor and SHGC.  See Figure 3-6.

Figure 3-6 – Example of Dynamic Glazing Type - Integrated Shading System
Source: NFRC Dynamic Glazing Products Fact Sheet

Its unique rating “Variable Arrow” identifier help consumers/specifiers understand the “dynamics” of the product and allow comparison with other similar dynamic fenestration products. The following label references are;

1.   The Variable Arrow – If the fenestration product can operate at intermediate states, a dual directional arrow, (↔), with the word “Variable” will appear on the label. Some dynamic glazings are able to adjust to intermediate states allowing for a performance level between the endpoints. 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 what the default or de-energized performance level.

Figure 3-7 – Dynamic Glazing NFRC Label Stickers

Source: NFRC Dynamic Glazing Products Fact Sheet

H.   Chromatic Glazing

One type of dynamic glazing product uses a Chromatic type of glass that has the ability to change its performance properties, allowing the occupant to control manually or automatically their environment by tinting or darkening a window with the flip of a switch. Some windows and doors can change their performance automatically in response to a control or environmental signals. These high-performance windows provide a variety of benefits; including reduced energy costs due to controlled daylighting and unwanted heat gain or heat loss. While still a relatively new technology, they are expected to grow substantially in the coming years.  A view of Chromatic glazing in the open (off) and closed (on) position is shown in Figure 3-8 below.

Figure 3-8 – Chromatic Glazing
Source: Sage Electrochromics

3.5.10  DYNAMIC GLAZING COMPLIANCE    

A.   Integral Shading Device

To use the high performance values the following must be met:

1.   Must have a an NFRC Certified Label sticker; or

2.   When no NFRC is available then the default values from Table 110.6-A and 110.6-B must be used.

B.   Chromogenic Glazing

1.   Must have a an NFRC Certified Label sticker; and

2.   Automatic controls must be installed to receive best rated performance value.

3.   If no NFRC label but with automatic controls then default to Table 150.1-A maximum U-factor of 0.32 and Maximum SHGC of 0.25;  or

4.   If with an NFRC label, but no automatic controls then default to Table 150.1-A maximum U-factor of 0.32 and Maximum SHGC of 0.25; or

5.   If no NFRC and no automatic controls then the default values from Table 110.6-A and 110.6-B must be used.

C.   Window Films

Window films are Polyester film that offer crystal clarity and can be pre-treated to accept different types of coatings. There are three basic categories of window films:

1.   Clear (Non-Reflective);

2.   Tinted or Dyed (Non-Reflective); and

3.   Metalized (Reflective), which can be metalized through vacuum coating, sputtering, or reactive deposition or reactive deposition and may be clear or colored.

4.   Clear films are used as safety or security films and to reduce ultraviolet (UV) light which contributes greatly to fading; however, they are not normally used for solar control or energy savings.

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

6.   Metalized (reflective) films are the preferred film in most energy savings applications, since they reduce transmission primarily through reflectance, and are manufactured to selectively reflect heat more than visible light through various combinations of metals.

See Figure 3-9 below. NFRC Attachment Ratings Label which helps to identify the energy performance of Window Films. 

Figure 3-9 – Window Film Energy Performance Label

Source: NFRC Applied Film Products Fact Sheet

D.   Performance Window Film Compliance

To receive window film credit the following must be met:

•      The Performance Approach must be used to meet energy compliance;

•      NFRC Window Film Energy Performance Label is required for each different film applied; otherwise use the default TABLE 110.6-A and 110.6-B values must be used;

•    Windows films must have at least a 10 year warranty

E.   Glazed Doors

The following rules apply to doors with glass:

Any door that is more than one-half glass is considered a glazed door and must comply with the mandatory 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 Package A 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 is made up of less than 50 percent, the opaque part of the door is ignored in the prescriptive approach, but in the performance method it is assumed a default U-factor of 0.50.  The glass area of the door is calculated as the sum of all glass surfaces plus 2 inches on all sides of the glass to account for a frame.

3.5.11  Compliance Alternatives    

While the prescriptive requirements and mandatory measures establish a minimum level of performance, the opportunities to exceed the requirements of the standards are considerable. Some of these compliance options are discussed in this section while others are 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 with the prescriptive requirements.

A.   Fenestration Area

Beginning with the 2005 update to the Standards, no credit is offered through the performance approach for reducing fenestration area below the maximum allowed 20 percent of the conditioned floor area (CFA).

Data show that the average window area in single family homes is about 17.3 percent of the CFA. In multifamily buildings, the average window area is about 14.5 percent of the conditioned floor area. While these are averages, the variations are considerable as shown in Figure 3-10.

Figure 3-10 – Glass Area in Single Family and Multifamily Residence
(Source: Residential New Construction Database)

The Energy Commission made fenestration area less than or equal to 20 percent a neutral variable in the performance approach with the 2005 update and there is no change in this regard in the 2013 update. The Commission recognizes that area and orientation can have a big impact on energy use, but because these are so variable in buildings, the Commission does not want the energy efficiency of other building components to be eroded in buildings that have small fenestration areas. While there is no credit for fenestration area less than 20 percent of CFA, there is a penalty for buildings that have a window area that exceeds 20 percent of CFA. Such buildings are permitted only with the performance approach, where the standard design has a fenestration area equal to the proposed design, up to 20 percent of the conditioned floor area, and the glass area in the standard design is uniformly distributed among cardinal orientations. The proposed design has the exact proposed glass area and orientation.

B.   Orientation

Window and skylight orientation has a huge impact on both energy use and peak electric demand. Orientation is a compliance option that is recognized in the performance approach, since the standard design has windows uniformly distributed on the north, south, east, and west sides of the building.

C.   Improved Fenestration Performance

With the 2013 update, the weighted average U-factor has been reduced to 0.32 in all climate zones as indicated in Package A. This means there is less credit available for installing high performance fenestration that could be traded off or be used to avoid other measures, such as duct sealing and verification. However, choosing high performance fenestration which performs better than the prescriptive requirements can still earn some credit through the performance method. In air conditioning climates, choosing a window with an SHGC lower than 0.25 will reduce the cooling loads compared to the standard design.

The magnitude of the impact 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 is usually framed in wood, aluminum, vinyl, or composites of these. Frame materials such as wood and vinyl are better insulators than metal. Some aluminum-framed units have thermal breaks that reduce the conductive heat transfer through the framing element as compared with similar units that have no such conductive thermal barriers.

2.   Number of panes of glazing, coatings, and fill gases. Double-glazing, dynamic glazing with controls offers opportunities for improving performance beyond the dimension of the air space between panes. For example, special materials that reduce emissivity of the surfaces facing the air space, including low-e or other coatings and chromogenic glazing, improve the thermal performance of fenestration products. Fill gases other than dry air such as, carbon dioxide, argon, or krypton and chromogenic glazing – also improve thermal performance.

D.   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.

Windows that face south can be effectively shaded by overhangs positioned above the window. The ideal overhang is one that provides shade during the months when the building is likely to be in an air conditioning mode and allows direct solar gains in the heating months. This can be achieved because 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. Due to the potential effectiveness of south-facing overhangs, a prescriptive compliance option is offered. See the following section for details.

Shading is much more difficult 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 climates, the best approach is to minimize windows that face east and west. Landscaping features can be considered to increase comfort but cannot be used for compliance credit.

E. Reserved

F.  Exterior Shading Devices

The prescriptive Standards require fenestration products with an SHGC of 0.25 or lower in climate zones 2, 4 and 6 through 16. However, a fenestration product with an SHGC greater than 0.25 may be used with the prescriptive requirements if a qualifying exterior shading device is used. Exterior shading devices and their 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.

When exterior overhangs are used, the SHGC requirements of prescriptive
Package- A may be met if the calculated combination of the overhang and fenestration SHGC efficiency is equal or lower than 0.25.   

For compliance credit, exterior shading devices must be permanently attached as opposed to 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 with WS-03R form is to calculate the combined SHGC of windows and exterior shading devices. When exterior shades are required for compliance, they must also be listed on the CF1R form and documented on the plans.

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

Equation 3-:

 SHGC_combined = (0.2875 x SHGC_max + 0.75) x SHGC_min

All operable windows and skylights are assumed to have an insect screen and this is the default condition against which other window/exterior shading device combinations are compared. The standard case is a window with an SHGC of 0.25 and an insect screen with an SHGC of 0.76. For this default case, the SHGC of the window is the SHGC_min, and the SHGC of the exterior sunscreen is SHGC_max. Working through the math on the WS-03R form, SHGC_combined is 0.25. This means that any combination of window SHGC and exterior SHGC that results in a SHGC_combined of 0.25 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 which is equal or lower than the prescriptive criterion of 0.25. This method of combining the SHGC of the window with the SHGC of the exterior shading device is also used with the whole building performance approach.

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

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

G.    Interior Shading

There is no credit for interior aftermarket shading devices, although they can be effective in reducing solar gains and should be considered by homeowners. The Energy Commission considers these added interior shades 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; however, a default standard shade is still considered in performance calculations so that estimates of energy use are more realistic, and tradeoffs against other measures are more equitable.

H.     Bay Windows

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

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.

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 of Package A for prescriptive compliance. The opaque portion must either meet the minimum insulation requirements of Package A for the applicable climate zone or be included in a weighted average U-factor calculation of an overall opaque assembly that does meet the Package A requirements. For the windows, the U-factor and SHGC values may be determined either from an NFRC rating or by using default values in §110.6-A and §110.6-B. 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 package requirements, the project must show compliance under the performance approach.

I.     Natural Ventilation through Fenestration

Operable windows can be a source of ventilation air useful for improving indoor air quality by dilution of indoor air contaminants and moisture and “free” cooling. During periods when the outdoor temperature is lower than the desired indoor temperature and the indoor temperature is uncomfortably warm from solar gains through windows or from heat generated inside the house, windows may be opened for some or all of the cooling. Natural ventilation can reduce the need to run the air conditioner. Not only does natural ventilation save energy, but it can also provide better air quality inside the home.

When building envelopes are sealed to reduce infiltration, air exchange with the outside air is reduced which increases the need for a mechanical means of bringing in outside air.

Energy Commission sponsored research in California homes has shown that a significant number of home occupants do not regularly open their windows for ventilation. When building envelopes are sealed to reduce infiltration, air exchange with the outside air is reduced which increases the need for a mechanical means of bringing in outside air.

Starting with the 2008 update, it is mandatory to meet the requirements of ASHRAE Standard 62.2 which include mechanical ventilation and minimum openable window area requirements. This mandatory measure is discussed in greater detail in Section 3.6.1.

J.   Construction Practice/Compliance and Enforcement

The compliance and enforcement process, should ensure that the fenestration efficiency values, areas, orientation, etc. be indicated on the CF1R form and are also specified on the building plans. In 'addition, the same efficiency values of the actual installed fenestration products meet or exceed the efficiency values on the CF1R form.   For more information, see Compliance and Enforcement on fenestration in chapter 2 of this 'manual.