The Reference Joint Appendices JA1 contains a glossary of terms. The following terms either expand on those listed in the Reference Appendices or are provided here to better clarify compliance issues for the building envelope.
1. Fenestration Terminology
A. General Terms
The following terms are used in describing fenestration products.
1. Center of Glass U-factor, Solar Heat Gain Coefficient (SHGC) and Visible Transmittance (VT). The U-factor, SHGC and VT are measured only through glass at least 2.5 inches from the edge of the glass or dividers.
2. Clear glass: Little if any observable tint. An IG unit with an SHGC of 0.5 or greater.
Divider (Muntin). An element that actually 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.
Dynamic Glazing is glazing systems that have the ability to reversibly change their performance properties, including U-factor, Solar Heat Gain Coefficient (SHGC), and/or Visible Transmittance (VT) between well-defined end points.
Chromogenic is a class of switchable glazing which includes active materials (e.g. electrochromic) and passive materials (e.g. photochromic and thermochromic) permanently integrated into the glazing assembly.
Integrated shading systems is a class of fenestration products including an active layer: e.g. shades, louvers, blinds or other materials permanently integrated between two or more glazing layers.
Fixed glass: The fenestration product cannot be opened.
Gap Width. The distance between glazings in multi-glazed 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.
Grille. See Divider.
IG Unit. Insulating glass unit. An IG unit includes
the glazings, spacer(s), films
(if any), gas infills, and edge caulking.
Hard Coat. A pyrolytic low-e coating that is generally more durable but less effective than a soft coat. See separate glossary term for low-e coating.
Light or Lite. A layer of glazing material, especially in a multi-layered IG unit. Referred to as panes in §110.6 when the lites are separated by a spacer from inside to outside of the fenestration.
Low-e Coating. A transparent or semitransparent metallic coating applied to glazing that reduces the emittance of the surface and that usually affects the solar heat gain of the glass. Low-e stands for low-emissivity. The coating (or film) is generally between glazings in double-pane or triple-pane fenestration products.
Mullion. A frame member that is used to join two individual windows into one fenestration unit.
Muntin. See Dividers.
Nonmetal Frame. Includes vinyl, wood, or fiberglass. 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. Non-metal frames may have metal strengthening bars entirely inside the frame extrusions or metal-cladding only on the surface.
Operable. The fenestration product can be opened for ventilation.
Soft Coat. A low-e coating applied through a sputter process. See separate glossary term for low-e coating.
Spacer or Gap Space. A material that separates multiple panes of glass in an insulating glass unit.
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, usually vinyl or urethane, with a significantly lower conductivity.
Tinted. Darker gray, brown or green visible tint. Also, low-e or IG unit with an SHGC less than 0.5.
Visible Transmittance( VT). The ratio of visible light transmitted through the fenestration. The higher the VT rating, the more light is allowed through a window.
Window Film 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.
B. Low-e Coatings
Low-emissivity coatings are special coatings applied to the second or third surfaces in double-glazed windows or skylights. As the name implies the surface has a low emittance. This means that radiation from that surface to the surface it “looks at” is reduced. Since radiation transfer from the hot side of the window 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.
In the residential market, there are two kinds of low-e coatings: low solar gain and high solar gain. 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 ultra-violet portions of the sun’s radiation while allowing visible light to pass through. 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 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.
C. National Fenestration Rating Council
The National Fenestration Rating Council (NFRC) is the entity recognized by the Energy Commission to supervise the rating and labeling of fenestration products. NFRC list the Certified Product Directory, containing NFRC certified U-factors and SHGC values for thousands of residential fenestration products see 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 and SHGC in accordance with §10-111 procedures.
D. R-value
R-value is a measure of a material’s thermal resistance,
expressed in ft²(hr)°F/Btu. R-value is the inverse of U-factor. A higher R-value
and lower
U-factor indicate higher energy efficiency.
The rated R-value of fiberglass (batt) insulation is based
upon its fully expanded thickness and may be obtained from the Reference Joint
Appendices JA4, Table
4.6.2 or from the manufacturer’s literature. When the insulation is compressed,
the R-value is reduced. The most common insulation compression occurs with R-19
and R-22 insulation batts installed in locations with a nominal 6-inch framing
that is actually only 5.5 in. thick. To achieve its rated insulation value, an
R-19 batt of insulation expands to a thickness of six and one quarter inches. If
it is compressed into 2x6 framing with an actual depth of 5.5 inches, the
insulation
R-Value is lowered to 17.8.
E. Solar Heat Gain Coefficient
Solar heat gain coefficient (SHGC) is 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.
SHGCc is the SHGC for the center of glazing area; SHGC or SHGCt is the SHGC for the total fenestration product and is the value used for compliance with the Standards.
F. U-factor of Fenestration Products
U-factor is a measure of how much heat passes 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 Btu of heat loss each hour per ft² of window area per degree °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 windows, the frame losses can be significant.
The U-factor for the center of glazing area; The U value measured at the center of a glazing assembly is the U value of the glazing itself. Not accounting for the edge affect or the U-factor of the framing.
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 a directory of certified fenestration products, directly from a manufacturer's listing in product literature, or from the product label.
G. Fenestration Terminology
The following terms are used in describing fenestration products.
Center of Glass U-factor, Solar Heat Gain Coefficient (SHGC) and Visible Transmittance (VT). The U-factor, SHGC and VT are measured only through glass at least 2.5 inches from the edge of the glass or dividers.
Clear. Little if any observable tint. An IG unit with an SHGC of 0.5 or greater.
Divider (Muntin). An element that actually 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.
H. Dynamic Glazing:
1. Includes active materials (e.g. electrochromic) and passive materials (e.g. photochromic and thermochromic) permanently integrated into the glazing assembly. Electro-chromatic glass that darkens by demand or lightens up when more free daylight or solar heat is desired? Improved glasses decreases the Solar Heat Gain Coefficient (SHGC) in the summer and reduces heat loss in the winter and are glazing systems that have the ability to reversibly change their performance properties, including U-factor, Solar Heat Gain Coefficient (SHGC), and/or Visible Transmittance (VT) between well-defined end points.
2. Integrated shading systems is a class of fenestration products including an active layer: e.g. shades, louvers, blinds or other materials permanently integrated between two or more glazing layers and that has the ability to reversibly change their performance properties, including U-factor, Solar Heat Gain Coefficient (SHGC), and/or Visible Transmittance (VT) between well-defined end points.
I. Low-e Coatings
Low-emissivity coatings are special coatings applied to the second or third surfaces in double-glazed windows or skylights. As the name implies the surface has a low emittance. This means that radiation from that surface to the surface it “looks at” is reduced. Since radiation transfer from the hot side of the window 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.
In the residential market, there are two kinds of low-e coatings: low solar gain and high solar gain. 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 ultra-violet portions of the sun’s radiation while allowing visible light to pass through. 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 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.
J. National Fenestration Rating Council
The National Fenestration Rating Council (NFRC) is the entity recognized by the Energy Commission to supervise the rating and labeling of fenestration products. NFRC list the Certified Product Directory, containing NFRC certified U-factors and SHGC values for thousands of residential fenestration products see 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 and SHGC in accordance with §10-111 procedures.
K. R-value
R-value is a measure of a material’s thermal resistance,
expressed in ft²(hr)°F/Btu. R-value is the inverse of U-factor. A higher R-value
and lower
U-factor indicate higher energy efficiency.
The rated R-value of fiberglass (batt) insulation is based upon its fully expanded thickness and may be obtained from the Reference Joint Appendices JA4, Table 4.6.2 or from the manufacturer’s literature. When the insulation is compressed, the R-value is reduced. The most common insulation compression occurs with R-19 and R-22 insulation batts installed in locations with a nominal 6-inch framing that is actually only 5.5 in. thick. To achieve its rated insulation value, an R-19 batt of insulation expands to a thickness of six and one quarter inches. If it is compressed into 2x6 framing with an actual depth of 5.5 inches, the insulation R-Value is lowered to 17.8.
L. Solar Heat Gain Coefficient
Solar heat gain coefficient (SHGC) is 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.
SHGCc is the SHGC for the center of glazing area; SHGC or SHGCt is the SHGC for the total fenestration product and is the value used for compliance with the Standards.
M. U-factor of Fenestration Products
U-factor is a measure of how much heat passes 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 Btu of heat loss each hour per ft² of window area per degree °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 windows, the frame losses can be significant.
U-factor is the U-factor for the center of glazing area; U-factor is the U-factor for the total fenestration product and is the value used for compliance with the Building Energy Efficiency Standards.
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 a directory of certified fenestration products, directly from a manufacturer's listing in product literature, or from the product label.
N. Building Orientation
Orientation of the building, particularly walls and fenestration, can impact its energy use. Orientation is also critical for sizing and installing renewable energy sources, such as solar thermal collectors for domestic water heating and solar electric collectors to help offset electrical demand.
East-Facing- "East-facing is oriented to within 45 degrees of true east, including 45°0'0" south of east (SE), but excluding 45°0'0" north of east (NE)." [§100.1] The designation “East-Facing” is also used in production buildings using orientation restrictions (e.g., Shaded Areas: East-Facing).
North-Facing- "North-facing is oriented to within 45 degrees of true north, including 45°0'0" east of north (NE), but excluding 45°0'0" west of north (NW)." [§100.1]
South-Facing- “South-facing is oriented to within 45 degrees of true south, including 45°0’0” west of south (SW), but excluding 45°0’0” east of south (SE).” [§100.1] The designation “South-Facing” is also used in production buildings using orientation restrictions (e.g., Shaded Areas: East-Facing).
West-Facing- "West-facing is oriented to within 45 degrees of true west, including 45°0'0" due north of west (NW) but excluding 45°0'0" south of west (SW)." [§100.1]. The designation “West-Facing” is also used in production buildings using orientation restrictions (e.g., Shaded Areas: West-Facing).