Chapter 6: Windows and Doors To be used with the Guide to Building Energy Efficient Homes in Kentucky

Windows and Doors Connect the interior of a home to the outdoors Provide ventilation and daylight Are aesthetically pleasing

Windows and Doors Provide the lowest insulating value in the building envelope Are a major energy liability in new construction

Windows and Costs Heating and cooling costs are affected by: Window type Window size Window location

How Windows Lose and Gain Heat Conduction through the glass and frame Convection across the air space in double- and triple-glazed units Air leakage around the sashes and the frame Radiation through the glazing

Goals Goals of energy efficient windows are: Low U-factors Moderate to high transmission rates of visible light Low air leakage rates Low transmission rates of invisible radiation— ultraviolet and infrared light energy

Window Developments Thermal breaks to reduce heat losses through highly conductive glazing systems and metal frames Inert gas fills, such as argon and krypton Tighter weatherstripping systems to lower air leakage rates Low-emissivity coatings

Low-Emissivity Coatings Low-emissivity (low-e) coatings are primarily designed to hinder radiant heat flow through multi-glazed windows – some surfaces, like flat black metal, have high- emissivities and radiate heat readily – some surfaces, like shiny aluminum, have low- emissivities, and radiate little heat

Winter Heat Loss in a Double-Glazed Window

Summer Heat Gain in a Double-Glazed Window

Inert Gas Fills ARGON is the oldest ― twice as dense as air, and twice as good at insulating; late 80s KRYPTON is newer ― 4 times as dense as air; mid 90s DELTA-8 is the newest ― 8 times as dense as air, and twice as good as Krypton

Solar Heat Gain Coefficient The Solar Heat Gain Coefficient (SHGC) is the fraction of incident solar radiation admitted through a window. SHGC is expressed as a number between 0 and 1.

Climate Zones and SHGC The lower a window’s SHGC, the less solar heat it transmits.

SHGC Typical Window Treatment Solar Heat Gain Coefficients TreatmentWindow TypeSolar Heat Gain Coefficient* Double-paned window ⅛-inch glass0.76 ¼-inch glass0.70 Tinted ¼-inch glass0.58 Low-e window Typical range, clear glass0.34 to 0.40 High solar gain0.55 to 0.60 Low solar gain0.25 Venetian blinds¼-inch double glass0.46 White roller blinds¼-inch double glass0.22 Light, airy drapes¼-inch double glass0.50 Heavy drapes¼-inch double glass0.36 Shade screen, louvered sun screen¼-inch double glass0.36 *Fraction of sunlight that passes through the glass and window treatment. Assumes that sunlight strikes perpendicular to glass.

Multiple Paned Windows

Window Recommendations for Climate Zone 4 U-factor is the rate at which a window, door, or skylight conducts non-solar heat flow.

Window Recommendations for Climate Zone 4 The Solar Heat Gain Coefficient (SHGC) is the fraction of solar radiation admitted through a window, door, or skylight.

Window Recommendations for Climate Zone 4 Visible transmittance (VT) is a fraction of the visible spectrum of sunlight, weighted by the sensitivity of the human eye, that is transmitted through a window’s, door’s or skylight’s glass.

Window Recommendations for Climate Zone 4 Air leakage (AL) is the rate of air infiltration around a window, door, or skylight in the presence of a specific pressure difference across it.

Window Insulating Values Window insulating values are typically reported in U-factors. A weighted average that includes the frame materials Single-glazed U-factor of 1.0 Double-glazed U-factor of 0.50 Double-glazed, low emissivity U-factor of 0.40 or less

Fenestration An architectural term referring to the arrangement of windows in a wall IECC: ―Skylights, roof windows, vertical windows (fixed or moveable), opaque doors, glazed doors, glazed block, and combination opaque/glazed doors. Fenestration includes products with glass and non-glass glazing materials.

Window Anatomy

NFRC Label Image courtesy of NFRC

Windows: Placement Matters Un-shaded east facing requires  U-Factor and SHGC North facing allows  U-Factor and SHGC

ENERGY STAR ® Rated Windows

Economics of Energy Conserving Windows Type of Window Energy Savings* ($/yr) {Code minimum U – 0.48} Break-even Investment ($) U – 0.40, SHGC– U – 0.35, SHGC– *Savings are for a two-story home with 254 sq ft of windows and 2 exterior doors, located in Lexington, KY, with approximately x5 windows.

Window Surface Temperatures Inside Window Surface Temperatures in Cold Weather (75°F inside and 20°F outside)

Proper Window Installation Step 1: Make sure that the window fits in rough opening and that the sill is level. Step 2: Install window level and plumb according to the manufacturer’s instructions. Step 3: Use non-expanding foam sealant to seal between the jamb and the rough opening, or stuff the gap with a backer rod or insulation and cover the insulation with caulk.

Proper Window Installation Step 4: If using a housewrap air barrier, slide the top window flashing under the barrier and seal the barrier to the window jamb with long-life window flashing tape or other appropriate, durable sealant. Step 5: After interior and exterior trim is installed, seal the gap between the trim and the interior or exterior finish with long-life caulk.

Future Window Options Electrochromic Windows Solid Windows

Windows and Natural Ventilation Casement – open fully for ventilation

Windows and Natural Ventilation Double hung – half of area open Slider – half of area open

Windows and Natural Ventilation

Windows and Shading Windows may require additional shading. Overhangs

Windows and Shading Exterior shades and shutters

Windows and Shading Exterior shades and shutters

Windows and Shading Interior shades and shutters

Windows and Shading Landscaping and trees

Sunlight Direct Diffuse Ground reflected

Overhangs Summer Winter

Sun Angles Summer and Winter Sun Angles Degrees from Horizon at Noon Latitude (Degrees)July 21January 21 Covington/Newport Lexington/Louisville Madisonville, KY KY/TN border367131

Sizing Overhangs

Exterior Shades and Shutters

Interior Shades and Shutters These window treatments try to block sunlight that has already entered the room. Curtains Roll-down shades Venetian blinds

Landscaping

Doors

Accessible Design Exterior and interior door openings – 3 feet wide Bath and kitchens have adequate room for wheelchairs

Summary