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Window Sill 101: Definition With Pictures


Picture from the Window sill. Source: Canva

Window sills are an integral part of any modern home. Although they come in a wide variety of designs and materials, window sills offer a protective function and can be a decorative element as well. Read on for a closer look at what exactly a window sill is, including the different types and their purpose.

A window sill is a horizontal surface below a window. The purpose of a window sill is to help support the windows, keep them in place, stop water from getting under the window and keep the heat in your house. They can be made from different materials, like wood, stone, tile, or PVC. Window sills usually have two parts: the outer and inner trim pieces. They can also be used to hold plants or other decorations.

The different types of window sills


When it comes to distinguishing window sills, they can be generally categorized into two broad categories:

  • Interior window sills
Source: Canva

An interior window sill, sometimes also known as the stool, is a trim found at the bottom of the window facing the interior portion of the room. The primary purpose of the interior window sill is the storage of items in the form of a shelf or for the display of items. Other additional functions may include structural support for the window and protection from weather conditions. Interior sills are typically flat surfaces, and it’s essential to level them correctly and use accurate measurements to ensure the safety of the items you put on them.

  • Exterior window sills
Source: Canva

Exterior window sills are found on the outside of the window. The primary purpose of an exterior window sill is to protect from inclement weather. If the wall of a house is not thick enough, then windows that don’t feature sills are exposed to rain and snow. Exterior window sills are angled to guide water, moisture, and sludge away from the house’s interior.

What purpose does a window sill have?


The usefulness of a window sill in a building structure tends to go unnoticed by most people. However, the key functions that it performs cannot be ignored:

1. It upholds the structure of a window

Source: Canva

Window sills are an integral part of a building structure – they act as the window’s framing to keep it in place. Without a window sill in place, the opening of a given window would sway and shift unpredictably as the foundation settles. This could put the integrity of an installation at risk, resulting in cracks and uneven structure. If constructed and placed correctly, the window sill forms a sturdy base that prevents the rest of the window from shaking in case of a disturbance, acting as a brace to reinforce the wall.

2. It keeps water from seeping through the window

Source: Canva

Window sills are an essential part of a construction building project because they keep away water from the structure. Without a window sill, rain and snow can easily seep in through your windows, rot your wood structure, and eventually weaken the wall’s integrity around them. If your home doesn’t feature wooden frames, then your interior might be lined with drywall. If water finds its way to your windows and walls, it could break down the drywall, causing mold to grow and thrive behind painted walls for years. 

3. It helps to improve energy efficiency and provides acoustic insulation

Source: Canva

A window seal forms a seal between the window unit and the wall of your home, which helps stop draughts and leaks. As a result, you won’t need as much heat to keep your home warm during cold days, and your energy bills will decrease. A high-quality window sill can also help to improve the acoustic insulation of your house, reducing the transference of noise from outside the structure to inside and vice versa.

4. It can be used as an accessory

Source: Canva

You can elongate your window sills and use them as shelves. This space can be used to keep potted plants. Positioning your plants strategically on an elongated window sill will make it easy for them to get plenty of natural light and even water during rainy seasons (only in the case of external window sills). Furthermore, window sills form a creative decorative space that you can use to store accessories such as pictures, vases, candles, decorative stones, lamps, or even books.

5. It can serve as a rest area

Source: Canva

A nice wide interior window sill can be a great place to sit and relax as you take in the views outside your window. You can even use it as a workspace or a place where you spend time leisurely (consider converting it into a reading nook for this purpose)

Which material should you choose for a window sill?


In the past, window sills were predominantly made out of wood, but today, you have more options to choose from. Each material has different characteristics and values and benefits and drawbacks. Therefore, it’s essential to choose materials carefully for your needs. Here are some of the most popular materials for the manufacture of window sills:

1. Wood

Wood Window Sill. Source: Canva

If you prefer traditional windows, wood is an excellent choice for your window sills. Wood was one of the leading materials used in house construction for ages, and even today, it’s still quite popular. Some of the most popular wood species for window sills include solid oak, cherry, larch, maple, ash, beech, chestnut, and mahogany. If you want a more affordable option, a window sill made of pine wood is a great choice. Wood offers noteworthy thermal insulation properties, and it is also environmentally friendly and durable, especially if you choose hardwood species like larch or oak. 

Wood also has many other perks – wood window sills aid natural ventilation, help maintain an average humidity level, and some species like pine even have natural antiseptic properties. The visual appeal of wood cannot be ignored, and the fact that the material can be used in almost all design styles makes it a popular choice. Different wood species have other grains and textures, and if you want a distinct aesthetic in your interior design, wood is a top choice.

One of the most significant downsides of wood window sills is the poor moisture resistance. Because it’s a natural material, wood needs regular maintenance and special treatment to protect it against rot, fungi, and mold. Window sills made from the material also have to be protected from mechanical damage as they are prone to denting when overloaded with heavy objects. The expensive cost of natural wood is also another downside to keep in mind. Today, the market offers wood alternatives like particleboard or MDF, but these tend to swell when they contact moisture. 

Related article: 6 Reason Why Do We Need Windows in a Room

2. PVC

PVC Window Sill. Source: Canva

PVC window sills are arguably the most popular choice. They come in a wide array of finishes, colors, and dimensions. You can choose prefab models or simply pre-order any size, shape, and color, given the overall interior of the room and window design. PVC doesn’t have the desirable properties of natural materials like wood, and it’s not exceptionally environmentally friendly, but it has its perks. 

PVC window sills are resistant to moisture, temperature extremes, and chemical cleaning agents, making them one of the most durable options for starters. The customization options on the market guarantee that you’ll be able to find the right window sill for your existing interior. PVC window sills are very easy to maintain – all you need to do is regularly wipe them clean with a damp cloth dipped in a mild cleaning solution to get rid of dust and debris. Steer clear of abrasive cleaners that can damage the delicate surface. Another appealing factor about PVC window sills is the affordable price. That being said, you want to be careful when choosing cheap options as not all products are of high quality.

Related article: Effects of Sleeping in a Room Without Windows

3. Stone

Stone Window Sill. Source: Canva

To add a touch of luxury to your interior and/or exterior window sills, choose stone. You have options like granite, marble, slate, and limestone – they are all-natural, look stylish, and are resistant to moisture and fire. Stone window sills also resist damage from sunlight and typically retain their appearance for years despite being low maintenance. On the downside, stone window sills lack heat-insulating properties and can be pretty expensive. The installation process for this type of windowsill is also tricky and time-consuming. 

 You can also find window sills made of artificial stone. Corian is a good example – window sills made of this material have high thermal insulation and moisture resistance, and they come in a wide range of shapes, sizes, and colors. One of the main disadvantages of artificial stone is that it is highly susceptible to scratches and mechanical damage. 

4. Tile

Tile Window Sill. Source: Canva

Tile window sills are great for bathroom and kitchen windows. Tile is moisture and sunlight-resistant, plus it’s relatively easy to clean and maintain. The material is also affordable, and it comes in a wide variety of colors, patterns, and designs. Mosaic tile or tile with unique patterns can transform your window sill into a work of art.

Related article: How Messy is Window Replacement?

How wide should a window sill be?


The width of a window sill will mostly depend on how much space you have and the intended use. If it is more than a mere design element, it should be much wider than the window. However, as is the case for a standard window sill, you should consider some form of additional support. Generally, the assumption is that a window sill should be 3-5 cm (1.18-1.97 inches) wider than the window on each side. This provision is enough to wedge the sill in the gaps in the wall firmly.

Final thoughts

Window sills tend to be overlooked, despite their importance in providing structural support and protecting the structure from moisture damage. Be sure to take care of your window sills to ensure that they continue serving their purpose.

Zoltan Szatmari

Zoltan is a test and industrial engineer from Europe who loves learning anything new and working on small projects. When he is not working, he is usually hiking or going to the cinema :).

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