What Is the Purpose of a Windowsill?

Windowsills are more than a place to store knick-knacks and stage houseplants. Both the inside (called a window stool) and the outside of the sill are critical to the structure and function of the window. Often referred to as a window shelf or window bottom, the windowsill is the flat piece of the window frame that meets the bottom of the windowpane.

Window Stool vs. Sill—What is the Difference?

A windowsill is typically constructed of a single piece of wood or framing material. In a double- or single-hung window, this sill is bisected by the windowpane. The exterior part of the sill is often sloped to promote drainage. The interior portion of the sill—the part on the inside of the house—is level and referred to as a window stool.

What Is the Purpose of a Windowsill?

While windowsills do serve an aesthetic purpose, there’s more to their construction than meets the eye. Windowsills:

Offer structural integrity: By creating a solid base, a sill is important to a window’s overall strength and stability. It also holds the sash steady when the window is closed.

Improve your home’s energy efficiency: A sill keeps your window airtight. This prevents drafts and the loss of heat or air-conditioned air to the outside.

Protect homes against the weather: The outer sill is angled so that the water or snow drains away from the house.

How to Replace a Windowsill

All windows have a windowsill. Over time, this part may weather, decay, or be damaged. Further, you may wish to alter the width of the sill or stool to better match the style of your home.

Windowsills and stools should always be replaced by a skilled professional—this will ensure your window maintains its functionality.

During windowsill replacement, a reputable service professional will:

Inspect the window. Your service professional will carefully inspect the window for signs of damage to parts outside of the sill or stool. If damage is detected, we’ll walk you through your options for a more extensive repair or a total replacement.

Prepare the space. Before construction begins, your service professional will remove the trim and any hardware that may impede the replacement.

Remove the existing sill. We will carefully remove the existing sill.

Measure and design. Understanding the structural importance of the sill and your design goals, your service professional will use either a pre-cut sill or cut a custom sill to install.

Install the windowsill. We’ll carefully install the new sill, ensuring that it’s level and secure.

Add the finishing touches. Now that your windowsill is fixed in place, all that’s left is caulking any cracks and sanding any rough edges.

If you have a damaged windowsill, your local Mr. Handyman, a trusted Neighborly brand, offers a window frame repair service. If you need a window repair or replacement, your local Glass Doctor has the expertise to get the job done right.

Find Expert Help for Your Windowsill Projects

Although they are often mistaken as insignificant decorative pieces, windowsills are an important part of the function and efficiency of your windows.

Whether you’re looking to replace your windows to better match your home décor, or because your windowsills are no longer structurally stable, your local Glass Doctor can help with window replacement and the Neighborly Done Right Promise. This ensures your window replacement job is done to your complete satisfaction. To get started, call (833) 974-0209 or request a estimate online today.