Window Sills: 8 Steps to Replacing It

Do you know what role a sill play in your window installation and why it is really an important component to have in your home? Little things are often overlooked and often unappreciated or even undervalued, but most times, they are what keeps the so-called main things in shape and helps them function as they should. This article would help you understand all you need to know about the window sill.

Many people when talking about installing or replacing windows usually have their thoughts only on the window itself forgetting about other essential components that help the overall functionality of the window.

For starters, what's a window sill? A window sill (also referred to as window bottom, window ledge) is the horizontal, flat structure at the base of the window unit.

Window Sills structure

The window sill is a part of the window trim. A window trim consists of the head casing above, the side jambs by the right and left the sill at the base, and the apron below the sill. They collectively help to make the window functional and sound.

Types of a Window Sill

Based on the placement (I.e. location) of the sill, there are two general types: interior and exterior window sill. An interior window sill is constructed on the inside of the window while the one installed on the outside of the window is called the exterior window sill. And at times, a window sill might be constructed in a way that covers the width of the wall from the inside right to the outside and thus will be seen both on the in and outside.

Types of a Window Sill

Though a school of thought held by some believes that a sill can only be found on the outside of a home and that what is popularly and commonly referred to as internal sill is properly termed ‘window stool', yet even many window experts refer to the stool as a sill.

Functions of a Window Sill

Generally, a window sill helps to support and hold the window in place. The solid sill on the bottom helps eliminate changes in the window frame and offers additional window stability and support.

window sill parts

Internal sills are mainly used for decorative and practical purposes such as displaying photos, plant pots, small household items, books, and other creative purposes that the homeowner can come up with.

The external sill on the other hand serves a lot more important purposes as it offers additional protection from moisture, weather, and rain and contributes to the overall energy-efficiency of the window as it keeps the home warm and thus saves you some energy bills. Without the window will, water can and will seep in and damage the walls and interior structure of the home and also valuable properties.

The sill also helps to effectively hold the sash in place when the window is closed by providing a stopping place for the lower rail of the window.

interior window sill

When installing an external sill, it should be done at an angle of about five to eight degrees to the outside to redirect water away from the window frame and building during rainy seasons. A perfectly level exterior window sill would allow for water retention on the sill causing rots to the sill and leaks into the home thereby defeating its intended purpose.

A quality exterior window sill will prevent mold growth and damage to the facade.

Interior sills, on the other hand, are installed on a flat surface and is to be correctly leveled to ensure that items placed on it don't fall off.

Creative Ideas for Interior Window Sills

Creative ideas for interior window sills

  • Window seat: You can place your favorite comfy chair near your interior sill and it comes with a great view too.
  • Worksurface: In small apartments, using the window will as a work area is a good solution. It also gives the additional benefit of using natural light
  • Storage Area: The kitchen window will be used to store cooking ingredients, spices, and lots more.

interior window sills storage area

  • To conceal a Secret safe

Window Sill benifits

  • It is also an ideal place to place flower pots and even grow herbs since there is plenty of sunlight.

place flower pots wih sill

Materials Used to Make a Window Sill

While appearance is majorly considered when choosing materials for an interior window will, a material that is weather-resistant, tough, and durable must be considered for an external window sill.

Window sills can also be made using different materials such as wood, stone, marble, tiles, uPVC, aluminum.

window sill material

In earlier times, wood was the most preferred material for the window will as it was inexpensive and easy to get. But one disadvantage of wood is its tendency to breed ants and even worse; termites. It also is prone to decay. To elongate its life span, a wooden window sill should be painted or sealed with waterproof material. But even with this treatment, wood eventually succumbs to mold and rot. They are better used therefore for internal window sills.

  • Stone Window Sill

Stone Window Sill

Stone Window Sills (among which are marble, natural stones, and granite) are attractive as well as long-lasting. They don't need extra treatment as they are naturally water-proof and also fire-resistant and marbles come in a wide range of colors to select from. Though they are a bit more expensive to buy and maintain.

  • Tile Window Sill

Tile Window Sill

Tile window sills are less common and can usually be found in older houses and used mainly in toilets and kitchens. They are however attractive and quite durable too.

  • Aluminum Window Sill

Aluminum Window Sill

Aluminum window sills are affordable. But it makes a lot of noise as raindrops hit its surface. This can however be remedied by including noise suppression tapes on it.

  • Plastic Window Sills

Plastic Window Sills

Plastic window sills can appear like stone or wood. They also are waterproof and do not mold

Caring for Your window Sill

Just as you care for other elements of the home, you also need to maintain your window sill regularly to make it last longer and look neat.

Caring for Your window Sill

Like any other element of your home, the window sills need regular maintenance. Use a vacuum cleaner to remove dust, dirt, and other unwanted things on the will.

Clean window sills with distilled water or wipe them down after spraying it with rubbing alcohol

Black spots on the window sill is an indication of mold. This is a health hazard and needs to be removed immediately.

To reduce the frequent rate at which you need to clean your window will, you can apply a thin film of floor wax to it, this makes water drip faster from the will and also aids quick dirt removal.

Replacing a Window Sill

Replacing a Window Sill

Time will eventually come when the need will arise for you to change your window sill, either because it's rotting or you just want to give your home a new look. You can choose to engage the services of professionals or you can take it on as a DIY project with the right tools at hand.

Tools Needed Include

  • Hammer
  • Pry bar
  • Nails
  • New sill
  • Waterproof filler like caulk
  • Paint
  • Step 1

Remove the old window will using a pry bar. This should be done with utmost care to avoid causing damage to the window glass and walls and to also kept the old will intact as it will be needed to be measured when cutting or getting a replacement. For sills that span the entire width of the window from the inside to the outside, it might require removing the entire window.

window removing using pry bar

  • Step 2

Cut out the remaining ends of the old sill with a hammer and chisel. Clean all traces of old glue and remove all the nails using pincer pliers.

old sill removing with a hammer

  • Step 3

Fix and crack on the wall and allow the area to dry out completely before installing the new window will.

Fix and crack on the wall

  • Step 4

Take measurements of the old sill onto the fresh wood and saw out the new window will use a table saw.

Take measurements of the old sill

  • Step 5

Attach the new sill (of exact length with the old sill) and tap in with a dead blow mallet

  • Step 6

Secure the sill using 2″ long nails through the outer edge of the will into the window frame

  • Step 7

Fill in all gaps around the edges of the new window sill with caulk. Do this thoroughly to avoid water seeping into the wood thereby causing a need for frequent replacement

  • Step 8: Paint the new sill

Note that when installing an exterior window will, check for the angle where the window sill meets the casing. The original sill was sloped so water would drain off, and the new sill needs to duplicate that slope.

Paint the new sill


One of the primary reasons for installing windows and having a home generally is to protect one and one's belonging from harsh weather elements, then of what use is a window that can't serve its purpose because of a window without the window sill is no window at all.

So ensure you pay proper attention to your window sills and let them add glamour, elegance, and at the same time protection to your home both interior and exterior.

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