Definition
The horizontal bottom piece of a window or door frame. Interior sills provide a shelf; exterior sills slope outward to shed water.
Related Terms
Argon Gas
An odorless, colorless gas used to fill the space between panes in insulated glass units. Argon is denser than air and reduces heat transfer, improving the window's insulating ability by 30-40%.
Awning Window
A window hinged at the top that opens outward from the bottom. Provides ventilation even during light rain because the open sash acts as an awning.
Bay Window
A window that projects outward from the exterior wall, typically with a large center window flanked by two angled side windows. Creates a wider interior shelf and more natural light.
Bow Window
Similar to a bay window but with four or more windows arranged in a gentle curve rather than angled segments.
Brick Mold
A type of exterior window trim (casing) originally designed for installation in brick openings. Now used generically for many window frame types.
Casement Window
A window hinged on one side that swings outward like a door using a crank mechanism. Provides excellent ventilation and an unobstructed view when open.
Casing
The trim material installed around the interior and exterior perimeter of a window or door frame. Covers the gap between the frame and the wall.
Cladding
A protective layer applied to the exterior of a wood window frame — typically aluminum or vinyl. Provides weather protection while maintaining the wood interior appearance.
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