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Window Stool vs. Sill: What Are The Differences?

Window Stool vs Window Sill

Most people haven’t heard the term window stool, and what is commonly called the windowsill is not actually the sill. In most cases, this is not an issue because it is a common misunderstanding that most people will understand.

However, imagine trying to order windows, and you ask for a particular windowsill style. What comes in for you may not be what you had in mind if the salesperson doesn’t ask clarifying questions. Or what if you are trying to troubleshoot a problem with your window over the phone with a contractor? Once again, if they don’t ask any clarifying questions, their advice may be unintentionally inaccurate, leaving everyone frustrated.

Below, we will learn the differences between a window stool and sill and their functions.

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Overview of a Window Stool

window stool
Image By: evasaves1, Shutterstock

Some people like to grow potted flowers on it, others put their children’s art crafts on it to dry in the sun, and most people assume it’s called the windowsill. However, this part of your window is called the stool. Another term for it is window ledge. Most windows have some form of stool. The size and style will be dependent on how thick the wall is compared to the window frame.

When doing home renovations or just sprucing up a room, the window stools are often an easy way to breathe life into the room. Depending on the material they are made from, sometimes they can be sanded and painted or just changed altogether.

Common Materials Used for a Window Stool

Window stools vary in construction between residential and commercial applications. In residential scenarios, they will generally be wooden. And in a commercial building, they are often metal. Another material growing in popularity in both commercial and residential is Corian.

Corian is a highly durable material made from acrylic polymer and alumina trihydrate. It is available in many colors and patterns. A significant reason it is an excellent choice for a window stool is being unaffected by moisture. And moisture is generally a common concern with windows, especially cheaper or old ones.

man insulates the window
Image Credit: Aleksey Kurguzov, Shutterstock

Window Stool Recap:

  • Commonly called a windowsill
  • Replacing or refinishing is an easy way to spruce up a room
  • Made from different materials depending on the application
  • Corian is growing in popularity as a material in window stools

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Overview of a Windowsill

window sill
Image Credit: Samir Lyctum, Shutterstock

Even though they are technically different, many professionals use the term windowsill interchangeably with a stool. Due to this common misconception, confusion can quickly arise when discussing a repair or replacing window components.

So, we’ve talked about what a windowsill isn’t. What is this elusive part of the window? The sill is basically the same as the stool, but it’s on the outside of the window and has a different purpose. While the stool is mostly for aesthetic finishing of the interior, the sill serves to help strengthen the window opening’s structure, protect against the rain or melting snow and adds to thermal protection to increase energy efficiency around the window.

If you were to take the shelf off the inside of your window, it would look terrible, but your window would still function normally and effectively. However, if you were to take the sill away outside, your wall and floor would be damaged by water during the first rain. There would be nothing to hold the window sash in place (the sash is the lower part that the window closes into). Finally, it would jeopardize the structural integrity around the window opening.

Can a DIYer Replace a Windowsill

Replacing a windowsill is an advanced DIY project but can still be done with a bit of guidance and the right tools. Before you begin this project, make sure that you find a thorough guide and prepare accordingly. Because if done incorrectly or left undone will leave the inside of your home open to water damage. Also, when it comes to resale, windows are a fairly big deal as they contribute directly to a home’s heating a cooling efficiency. So, you’ll want to ensure everything is done correctly and to code.

old window sill
Image Credit: nadja-golitschek, Pixabay

Windowsill Recap:

  • The term is mistakenly used to refer to the window shelf quite often
  • Unlike without the shelf, a window will not function correctly without the sill
  • An experienced DIYer can change it

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Why is the Difference Important?

Without knowing their functions are different, window stools and sills often look the same at first glance. Both can be constructed with the same material. Even if they are both wood, the sill will likely be painted with exterior paint to prevent premature weathering or damage from moisture.

However, if the sill is damaged, the shelf cannot be switched to the outside. They will be different dimensions because of their different jobs. Different sizes are one reason it is essential to differentiate between the two when talking to a window supplier to order components for a window repair.

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A question about the difference between a window stool and a sill will not likely come up often. But, as we saw in this comparison, it can be an important distinction to make. It could literally be the difference between a couple of hundred dollars versus well over a thousand in a renovation or repair.

Now that you know the difference, you can make an informed decision about the components you need when you are online or at your local building center, even if the salesperson or website are using the terms interchangeably.

Featured Image Credit: Left: Window Stool: evasaves1, Shutterstock | Right: Window Sill: Samir Lyctum, Shutterstock


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