What is a Window Sill?

All of our lives, we’ve been told what a window sill is. It’s that ledge under your window, right? Well, sort of.

If you’ve ever looked at the anatomy of a window, you’ll notice that there are many parts:

  • Window frame
  • Window panes – You could have more than one.
  • Window sill
  • Latch lock
  • Grids (optional) – These are also called muntins.

If I gave you that list, you’d be able to point out to me each part pretty easily. A window, of course, has a lot more parts to it such as a head jamb, side jamb, apron, and more. However, in this article, we’re not going to be going over those things. I doubt you’ll be bringing up those very specific window terms in a normal conversation with someone. Unless… no never mind. That wouldn’t happen.

window anatomy

What if I told you that your current understanding of a window sill is wrong?

What is a Window Sill?

Part of what you know about window sills is right, but part of it is wrong too.

A window sill actually exists on the outside of your home, not the inside. A window sill is part of your window. When they ship you the window or your window manufacturer comes with the window, the window sill is already attached.

The inside ledge under your window is actually called the window stool. It looks like a shelf where you put random knick knacks. Maybe it also acts as a perch for your cat. A window stool is not part of your window. It’s part of your home. Whether you have a window or not in the window opening, you can still have a window stool.

window stool
Image via Canva.com

Despite these differences, you’ll still hear people (experts included) call the inside ledge a window sill.

Just clarify with them by asking, “Are you talking about the inside or outside ledge?”

You can learn more about the anatomy of a window here.

What Does a Window Sill Do?

Window sills actually have a purpose. They’re not just decorative.

They support your window and hold it in place. They also move rainwater away from your home. Typically, window sills are slightly inclined so water moves down and away.

Without this, the water would just run down your home’s walls. That doesn’t sound too fun, does it?

No one wants mold around their home. It can lead to breathing problems and other illnesses too.

Without the window sill, your windows might shift and move around as your foundation moves. The window sill stabilizes your window as things move.

Why is the Window Sill Angled?

Window sills have to be angled to protect your home against the elements such as rain and snow.

If the window sill is flat, then water could sit there for hours to days before it evaporates. This depends on what kind of climate you live in, of course.

Sitting water causes water damage to your home. If the sill tilts the wrong way, then the water would run into your home.

An angled sill leads the water down and away, like a rooftop.

Should I Call It a Window Stool?

Now you know what the window sill is and what the window stool is. Should you start calling it the “proper” word?

Most likely not.

This is strange, but the term “window sill” is still more widely used. If you’re searching for answers to a problem with your window stool, search it up using window sill instead.

Similarly, if you’re talking about it in public, use the term “window sill.”

If you need to specify inside vs. outside, then do that.

It’s better for other people to be able to understand you than to be proper. Even experts like local contractors need to be able to understand what you’re talking about to make good recommendations.

In order to not be confusing, it’s okay to use the same terminology as everyone else.

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