Window & Door Glossary

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Argon Gas: An inert gas used to fill the space between panes of insulated glass. Denser than air, it improves thermal performance by reducing heat transfer.
Awning Window: A window hinged at the top that swings outward from the bottom. Good for ventilation during light rain.
Bay Window: A window assembly that projects outward from the wall, typically with three panels at angles (usually 30° or 45°).
Bow Window: Similar to a bay window but with 4-6 panels arranged in a gentle curve rather than at angles.
Casement Window: A window hinged on the side that swings outward, operated by a crank mechanism.
Double-Hung Window: A window with two sashes that both slide vertically. Both sashes can typically tilt inward for cleaning.
Double-Pane / Dual-Pane: Glass unit with two panes separated by a sealed air space. Standard for energy-efficient windows.
ENERGY STAR: Government certification program identifying energy-efficient products. ENERGY STAR windows meet specific performance criteria for your climate zone.
ER (Energy Rating): Canadian rating system measuring overall window energy performance. Higher numbers are better.

Fixed Window: A window that doesn't open. Also called a picture window. Maximum light, no ventilation.
Frame: The main structure of the window that holds the glass and sash. Made of vinyl, wood, fiberglass, or aluminum.
Glazing: The glass portion of the window. Can refer to the glass itself or the process of installing glass.
Grilles / Grids: Decorative bars that divide window glass into smaller panes. Can be between glass, on surface, or true divided lites.
IGU (Insulated Glass Unit): A sealed unit of two or more glass panes with air or gas between them. The "sealed unit" in your window.
Low-E (Low-Emissivity): A microscopically thin coating on glass that reflects heat while allowing light through. Essential for energy efficiency.

Mullion: A vertical or horizontal bar dividing window units. Unlike grilles, mullions are structural.
R-Value: Measures resistance to heat flow. Higher numbers mean better insulation. (Inverse of U-factor.)
Sash: The frame that holds the glass and moves within the main window frame.
Sealed Unit: See IGU. The glass unit containing two or more panes sealed together.
SHGC (Solar Heat Gain Coefficient): Measures how much solar heat passes through glass. Lower numbers mean less heat gain (good for south-facing windows in summer).
Single-Hung Window: Similar to double-hung but only the bottom sash moves; top sash is fixed.
Spacer: Material separating the panes in an IGU. "Warm-edge" spacers reduce condensation and improve efficiency.

Tempered Glass: Safety glass that's heat-treated to be 4-5x stronger than regular glass. Breaks into small, less dangerous pieces. Required in certain locations.
Thermal Break: An insulating barrier within a frame (usually aluminum) that prevents heat transfer through the frame material.
Triple-Pane: Glass unit with three panes for maximum insulation. Recommended for Ottawa's extreme climate.
U-Factor: Measures heat transfer through the window. Lower numbers mean better insulation. Key energy performance metric.
Weatherstripping: Material around the sash that seals against air and water infiltration when the window is closed.