The Anatomy of a Window

When you’re in the market for replacement windows, or in need of window repairs, knowing the anatomy of a window helps you understand more about the issue you’re trying to solve, and communicate with contractors about specifics. New windows can lower your energy bills and bring greater comfort to your home interior—putting an end to the chilly drafts you once contended with each cold day. 

Let’s dive into the basics of every window so you can be well versed and ready to discuss window solutions for your home with a contractor. 

Window Components and Their Functions

Argon

Argon is the inert, nontoxic gas used in insulating glass units to reduce heat transfer and make your home more comfortable throughout the year. Argon gas enhances insulation and energy efficiency, and lowers utility bills. 

Check Rail

On a double-hung window, the check rail is the part of your window where the bottom of the upper sash and the upper part of the lower sash come in contact. This is also simply known as the middle of the window. 

Divided Lite/Grille

These are decorative bars that permanently adhere to your window glass (simulated divided lites) or are located between two panes of glass (grilles between glass) to add architectural interest on a window. 

Frame

This is the stationary part of a window that surrounds the glass or sash. The frame is composed of three parts: the header across its top, the jambs down each side of your frame, and the sill across its bottom. Window frames come in durable fiberglass, insulated vinyl, or classic wood. 

Glass Pane

This is the sheet of glass within a window frame. 

Hardware

Window hardware is an integral part of home design. It includes all of the mechanical and operable parts of the window such as its locks, crank handles, fasteners, and hinges used to secure it to protect your home from intruders. Hardware plays an essential role in window function, security, and aesthetics. In high-end homes, hardware elevates the space by providing a finishing touch that complements a house’s architectural style. 

Jamb

Window jambs are the main vertical parts forming the sides of a window frame. 

Jambliner

A jambliner is a strip which goes on the sides of a window frame to provide a snug fit for the window sash. 

Lift 

Commonly found on wood windows, a lift is a handle used for raising the lower sash in a single- or double-hung window. 

Low-E Glass

This is the extremely thin coating of special low emissivity (Low-E) metallic material applied to glass panes to boost a home’s energy efficiency and block out harmful UV rays (which prevent furniture and curtains from fading). 

Lower Rail

The lower rail is the bottom part of the lower sash. 

Muntin

These are the bars that form the decorative grille patterns on a window.  

Operator

This is the crank-operated device for opening and closing casement or awning windows. 

R-Value

The resistance a material has to heat flow is its R-value. Higher numbers indicate greater insulating capabilities. 

Rail

A rail is the horizontal part of a window sash made of the lower rail, the check rail, and the upper rail. 

Sash

A window sash is the operating or stationary part of the window that holds the glass and is separate from the window frame. 

Sash Lock

This is the locking mechanism used on a single- or double-hung window that engages with the lock strike to reduce rattling. 

Sill

A windowsill is the lower, horizontal piece of a window that supports the frame. 

U-factor

This measures how well a window keeps heat inside your house. A higher number allows more heat to escape. A lower number allows less heat to leak out. 

Upper Rail

The upper rail is the top part of the upper sash. 

Weatherstrip

This is a strip of resilient material used to cover the joint between your window sash and frame to decrease air leaks and keep moisture from penetrating your home. 

Get Beautiful, Energy Efficient Replacement Windows Installed to Perfection 

Don’t settle for old, worn-out windows that leak cold air into your warm home each winter, and drain your cool air each summer. Get stunning new windows to protect your home from the elements and boost its curb appeal and value. 

At Replacement Windows by Lakeside, we provide a high level of listening and care for every homeowner. As the exclusive distributor and authorized contractor for Infinity from Marvin in St. Louis since 2006, we ensure precise installation. Learn more about how our windows services boost your home’s energy efficiency and value.