The Energy Performance of Fenestrations

What is Fenestration?Fenestration: Any opening in a building's

envelope including windows, doors, curtain walls and skylights designed to permit the

passage of air, light, vehicles, or people.

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Examples of Fenestration

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Fenestration Options

• Windows and Doors

• Skylights

• Light tubes

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Window Terminology

• Frame: Perimeter that connects to wall• Glazing: Clear material that allows in light• Sash: Operable part• Sill: Where the sash sits• Mullion: Pane dividers• Panes: Individual glass pieces that

comprise a window • Jam: Extension that finishes out the wall

Windows Can Be Losers

• Windows can be the most important energy decision you make in a house.

• In older homes windows usually account for 1/3 of the total heat loss.

• New homes typically lose 15-40% of their heat through windows.

• Windows can also account for up to 75% of the heat gain in the summer.

The Good Stuff About Windows• Glazing technology has changed tremendously.

• The best windows insulate almost four times as well as the best ones ten years ago. From R-1 to R-4. With some as high as R-12.

• Windows allow light in for daylighting.

• Windows allow heat in for winter heating.

Features In Energy-Saving Windows

• Multiple layers of glazing 2…3…4• Thickness of air spaces- 1/4 to 1/2”• Low-conductivity gas fill- argon, carbon dioxide,

sulfur hexafluoride, krypton• Tinted glass coatings• Low E coatings

NFRC-National Fenestration Rating Council

NFRC is a non-profit organization that administers the only uniform, independent rating and labeling system for the energy performance of windows, doors, skylights, and attachment products.

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Low E Window Review

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Low-E Windows cont…

Low-emissivity (Low-E) coatings are microscopically thin, virtually invisible, metal or metallic oxide layers deposited on a window or skylight glazing surface primarily to reduce the U-Factor by suppressing radiant heat flow.

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Window U-Factor

• The U-factor measures how well a product prevents heat from escaping. The rate of heat loss is indicated in terms of the U-factor of a window assembly. U-factor ratings generally fall between 0.20 and 1.20.

• The insulating value is indicated by the R-value, which is the inverse of the U-factor. The lower the U-factor, the greater a window's resistance to heat flow and the better its insulating value.

Solar Heat Gain Coefficient

The Solar Heat Gain Coefficient (SHGC) measures how well a window blocks heat from sunlight. The SHGC is the fraction of the heat from the sun that enters through a window. SHGC is expressed as a number between 0 and 1. The lower a window's SHGC, the less solar heat it transmits.

Visible TransmittanceVisible Transmittance (VT) measures how much light comes

through a product. VT is expressed as a number between0 and 1. Heavily tinted products have a relatively low VT.

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Air LeakageAir Leakage (AL) measures how much outside air comes into a home or building through a product. AL rates typically fall in a range between 0.1 and 0.3. The lower the AL, the better a product is at keeping air out. AL is an optional rating, and manufacturers can choose not to include it on their labels. This label displays AL in U.S. units.

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Condensation ResistanceCondensation Resistance measures how well the window resists water build-up. The higher the condensation resistance factor, the less build-up the window allows. Condensation Resistance is scored on a scale from 0 to 100. The Condensation Resistance rating is useful when comparing different products. ENERGY STAR qualification is based on U-Factor and SHGC ratings only.

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Heat Loss and Gain• Windows are strongly affected by solar radiation and the

airflow around them. R-value does not accurately reflect this interaction. Therefore, the window industry measures the energy efficiency of their products in terms of thermal transmission, or U-factor.

• U-factor measures the rate of heat transfer through a product. Therefore, the lower the U-factor, the lower the amount of heat loss, and the better a product is at insulating a building.

Windows, doors, skylights can gain and lose heat in the following ways:• Direct conduction through the glass or glazing, frame, and/or door• The radiation of heat into a house (typically from the sun) and out of a house from room-

temperature objects, such as people, furniture, and interior walls• Air leakage through and around them.

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Windows Performance

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One of the best ways to measure the effect of windows on building energy use is known as a U-factor rating.

Energy Performance of Windows

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A window's energy efficiency is dependent upon all of its components:• Frames

There are advantages and disadvantages to all types of frame materials. Overall, vinyl, wood, fiberglass, and some composite frame materials provide greater thermal resistance than metal.

• Glazing or Glass There are many types of glazing available for windows, especially since many glazing technologies can be combined. These window glazing technologies include the following:Gas fills, Heat-absorbing tints, Insulated (double-glazed, triple-glazed), Low-emissivity (Low-E) coatings, Reflective coatings, Spectrally selective coatings.

Types of Operable Windows

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OperationAwningHinged at the top and open outward. Because the sash closes by pressing against the frame, they generally have lower air leakage rates than sliding windows.CasementHinged at the sides. Like awning windows, they generally have lower air leakage rates than sliding windows because the sash closes by pressing against the frame.FixedFixed panes that don't open. They're airtight but not suitable in places where window ventilation is desired. HopperHinged at the bottom and open inward. Like both awning and casement, they generally have lower air leakage rates because the sash closes by pressing against the frame.Single- and double-hungBoth sashes slide vertically in a double-hung window. Only the bottom sash slides upward in a single-hung window. These sliding windows generally have higher air leakage rates than projecting or hinged windows.Single- and double-slidingBoth sashes slide horizontally in a double-sliding window. Only one sash slides in a single-sliding window. Like single- and double-hung windows, they generally have higher air leakage rates than projecting or hinged windows.

Proper Window Flashing Is Crucial

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Window Flashing Details

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Skylights-

• Electric and manual venting type

• Simple Installation• Designed for deck

mounted, installations, self flashed, and curb mounted applications

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Light Tubes

Advantages: • Typically lower cost

than conventional skylights

• Typically few or no modifications to a structure

• Longer longevity due to simple design

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Glass Block• Solar Reflective Glass Block

Developed in response to calls from architects and builders for a glass block product capable of reducing solar energy gain. A metal oxide coating controls the passage of sunlight, creating a more comfortable environment for home or office. Each glass block is individually coated, which creates a customized appearance to each individual block. In addition, similar to the original Pittsburgh Corning Glass Block, Solar Reflective Glass Block continues to offer ample light transmission while reducing noise. It is a popular choice for commercial and institutional buildings and high-end residential projects.

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Glass block cont…Is glass block load-bearing?

Glass Block is a non-load bearing material. Provisions (i.e., lintels) at the head should be provided to accommodate the support of loads above the glass block panel (similar to doors and windows).

What is the R-value of glass block?

The R-value for Premiere Series glass block is 1.96, which is more than twice the value for flat 1/8" sheet glass windows or roughly equivalent to a double pane thermal window. The Thinline™ Series R-values are slightly lower at 1.75.

www.pittsburghcorning.com; low-e INSOLAR glass block

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Frame Construction

• Commonly made of wood(most common), Aluminum, vinyl (PVC) and fiberglass

• Heat conduction is a problem with Aluminum. Need a thermal break

• Some vinyl frames insulated with fiberglass are better than wood.

• Edge spacers separate the panes. If metal they need a thermal break

Other Efficiency Options

• Clear plastic on inside• Repair weather stripping• Storm windows• Insulation shades• Pop in panels or shutters• Close curtains• Clean

Recommendations

• Look for National Fenestration Rating Council label• Look for energy saving features- doubleglazing,

Low-e coatings, low-conductivity gas fill, and wood, vinyl or fiberglass frames.

• Consider different glazings for different sides• Choose large unbroken glazing instead of small

panes• Look for good warranties on gas fill