WINDOWS
WINDOWS
WINDOWS
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GENERAL INFORMATION
GENERAL INFORMATION
GENERAL INFORMATION:
Selecting the right windows can save energy and affect resident comfort.
Window installation will have an impact on building durability (water control) as well as energy use and resident comfort.
There are three main components of windows that affect performance: the glazing, the frame, and the spacer (material or system that separates the glass panes).
Window frames are available in a wide range of materials. Common materials for windows include wood, vinyl, aluminum, and fiberglass.
Glazing choices affect how much light the window will transmit and how much of the sun’s heat they allow into interior spaces, and how well they prevent the flow of heat.
The spacer is the component that separates two panes of glass from one another and holds them at a fixed separation. Older double-pane glazing units typically have metal spacer that are highly conductive. This can increase the risk of condensation on the glass near the window frame. Newer high performance windows have thermal spaces that help maintain resistance to heat flow at the perimeter of the glazing unit.
Window rating are based on three primary classifications:
U-factor, the amount of heat that a material conducts (lower is better).
Solar Heat Gain Coefficient (SHGC), a measure of how much of the sun’s heat energy is transmitted through the glass.
Visual Transmittance (VT), is the percentage of visible light transmitted through the glass.
Two other voluntary criteria (not required to be included on NFRC labels) are also important to window performance:
Air leakage
Condensation resistance
Considerations for historic buildings:
Historic buildings may have restrictions on the type (operation) of window, the frame material, and certain panning details.
For projects using historic tax credits, all window details will have to be reviewed by local governing authorities.
REQUIREMENTS
REQUIREMENTS
requirements
safety requirements:
POAH and POAH Communities Window Limiter Policy: Windows should be limited to opening 4” maximum.
required details:
For each unique window type or wall assembly provide details for the head, sill, and jamb conditions.
The details must clearly demonstrate the water control for the window opening (flashing and drainage).
PERFORMANCE REQUIREMENTS:
Windows must comply with local energy code.
To verify if specific window energy properties comply with the local code requirements, look for the NFRC label.
The National Fenestration Rating Council (NFRC) label is needed for verification of energy code compliance. The NFRC label displays whole-window energy properties and appears on all fenestration products which are part of the ENERGY STAR program (www.nfrc.org).
Proper window installation is necessary for optimal performance, to avoid air and water leakage. Always follow manufacturers’ installation guidelines and use trained professionals for window and skylight installation.
Windows must be ENERGY STAR certified. Often energy star certified windows meet or exceed energy code requirements. Follow this link to determine the minimum U-Factor and Solar Heat Gain Coefficient (SHGC) for your area.
Window performance can also be based on location and climate zone. The more stringent requirements between ENERGY STAR and the local energy code must be followed.
Climate Zone Map from the 2021 International Energy Conservation Code
AC SLEEVE IN WINDOW SASH
AC SLEEVE IN WINDOW SASH
AC SLEEVE IN WINDOW SASH
Required Details:
Physical Sizing: all AC units must be sized to fit the thru-wall sleeve.
Thu-wall Sleeves: insulate and seal the perimeter of the wall sleeve to avoid drafts. Make sure thru-wall sleeves drain condensate to the exterior.
Insulated AC Covers for Winter Use: all thru-wall sleeves should be covered during winter months with an interior, hard-plastic, insulated cover. Use covers that are deep enough to go over both the sleeve and the AC unit so AC units do not need to be removed during winter months. See the AC Cover section of the Basis of Design for more information.
Use energy efficient AC unit: See the AC Unit section of the Basis of Design for more information.
preferred strategy:
POAH’s preferred strategy for in-window AC units is to install a new insulated sash panel with integral AC sleeve. The details shown below may need to be modified for each specific window condition.
Through-wall AC units in a panel fixed within the window. View from interior.
View from exterior.
WINDOW OPERATION
WINDOW OPERATION
WINDOW OPERATION:
SLIDER
WindowWellExperts.com
CASEMENT
WindowWellExperts.com
AWNING
WindowWellExperts.com
HOPPER
WindowWellExperts.com
FIXED
WindowWellExperts.com
SINGLE HUNG
WindowWellExperts.com
DOUBLE HUNG
WindowWellExperts.com
TERMS & VOCABULARY
TERMS & VOCABULARY
TERMS & VOCABULARY:
Copyright © 2016, Efficient Windows Collaborative.
Copyright © 2016, Efficient Windows Collaborative
U-Factor
The rate of heat loss is indicated in terms of the U-factor (U-value). This rate of non-solar heat loss or gain through a whole window assembly is measured in Btu/hr-sf-°F. The lower the U-factor, the greater a window’s resistance to heat flow and the better its insulating value.
Copyright © 2016, Efficient Windows Collaborative
Solar Heat Gain Coefficient (SHGC)
The SHGC is the fraction of incident solar radiation admitted through a window. SHGC is expressed as a number between 0 and 1. The lower a window’s solar heat gain coefficient, the less solar heat it transmits. Whether a higher or lower SHGC is desirable depends on the climate, orientation, shading conditions, and other factors.
Copyright © 2016, Efficient Windows Collaborative
Visible Transmittance (VT)
The VT is an optical property that indicates the amount of visible light transmitted. VT is a whole window rating and includes the impact of the frame which does not transmit any visible light. While VT theoretically varies between 0 and 1, most values are between 0.3 and 0.7. The higher the VT, the more light is transmitted.
Copyright © 2016, Efficient Windows Collaborative
Air Leakage (AL)
AL is expressed in cubic feet of air passing through a square foot of window area (cfm/sf). The lower the AL, the less air will pass through cracks in the assembly. AL is very important, but not as important as U-factor and SHGC.
Copyright © 2016, Efficient Windows Collaborative
Condensation Resistance (CR)
CR measures how well a window resists the formation of condensation on the inside surface. CR is expressed as a number between 1 and 100. The higher the number, the better a product is able to resist condensation. CR is meant to compare products and their potential for condensation formation. CR is an optional rating on the NFRC label.