Speak Like A Home Improvement Pro: Common Window Terminology

When it comes to windows, we all know what a pane or sill is, but how about a sash, grille, or mullion? Knowing the different parts of a window can help you make better decisions as a homeowner.

By understanding window components, you can properly maintain your windows, and you will know which options are best for your home when it’s time for a window repair or replacement. Plus, understanding these window terms will help you better communicate with your contractor, creating a smoother remodeling experience.

Apron

The piece of decorative trim beneath the stool against the interior wall.

Casing

The decorative frame around the window, covering the space between the window frame or jamb and the wall. Also know as casement moulding.

Frame

The wood or vinyl attached to your house that surrounds and supports the window system. The parts of the frame include the head, jambs, and sill.

Mullions & Grilles

Mullions are decorative pieces that only divide the window visually, giving the glass the look of multiple panes. Muntins are the grid shaped pieces that divide windowpanes not commonly used today.

Jambs

The vertical wood or vinyl pieces on the sides of the window frame.

Rail (or Meeting Rail)

The horizontal pieces of the window sash composed of the lower rail and upper rail.

Sash

A sash is the part of the window that uses framing to actually hold the glass in place. For example, in a standard double-hung window there are two sashes, one upper and one lower. One or more sashes then join at the rail and sit inside of the jambs.

Sill

The horizontal part at the bottom of the window frame exterior. Usually this piece touches the lower sash and stool when the window is fully closed.

Stool

Often referred to as the sill, the stool extends from the bottom rail of the sash inward.

Glass Package

Modern windows usually consist of two or more panes of glass with space between them. The panes are either held in place by groves in the sash or are held at a precise distance using a product known as a “spacer.” Spacers usually give the panes an air-tight seal to hold gasses that improve the energy efficiency of the window.

R-Value

The measurement of how well insulation materials can resist heat. The higher an R-value, the better the insulation performance will be.

U-Factor

The inverse of the R-value, the u-value is the rate of heat loss from a home and is the more common measurement in windows. The lower the U-value, the better a window will resist heat flow and insulate your home. While a lower U-rating is better, lowest does not mean best. A very low U-rating tends to be manipulated and disproportionally increases the cost of the window.

Weather-stripping

The material that covers the bottom of the lower sash and top of the upper sash to reduce air leaks and prevent water from getting in.

Weep Hole

Purposeful openings in the window sill that allow water and condensation to drain or escape to the outside of your home.

Now that you are familiar with all the parts of your windows, inspect them inside and outside of your home. Make minor repairs right away to save energy and keep your home at a comfortable temperature. Check for warning signs that your windows need to be replaced. And when it’s time, schedule a no-pressure consultation with one of our window replacement experts. They will consider your unique home and budget requirements to come up with the right solution for you.