2 Easy Ways to Replace Window Sills (Step By Step Guid)

A time will come when you need to replace your window sills due to damage. Isn't it?The causes of such losses range from a poorly performed initial installation to a poorly constructed building structure. It is easy to repair the sill, but it can be challenging to deal with the procedure's root cause.This article will guide you on what steps to take to ensure a proper replacement of your window sill.

Sills are fixed on the outside of a window ledge. This forms the weathering part of an opening, which protects the building fabric below the window opening. When rain falls on the window, it drips down and lies on the ledge when the sill is not fixed. This can eventually cause dampness to the wall below. This also may allow water to seep through, causing efflorescence. Another issue can be having rain tears appearing on the building facade below the window.

Window Sill

Window sills can be inbuilt during construction or after the building construction. Different types of sills are available in the market. This may include clay, concrete, stone, or wood. Each type has its advantages, and preference is on the homeowner to choose the desired variety. When using the in situ ones, they should be protected until the finishes stage is complete. The wood typeis used in dry areas due to the vulnerability of the weather.

The clay or concrete sills are usually fixed after the window frame is in place. All sills should be done with an overhang or projection from the wall. This should be a minimum of two or three inches from the wall. They should also have a fall to ensure water and dirt flow away. They should be about one inch in thickness. It is crucial to ensure that they are placed almost half an inch above the bottom frame. This will allow the sash to open without touching them.

window sill replacement

The fixing of sills starts with measuring the projection and window recess into the wall. This is measured from outside. The window ledge is then made level. The first and last sill is then bedded on strong mortar. A string and spirit level is used to align the top and overhang distance. It is essential to recess them two inches into the wall on both ends. The rest is then bedded on the mortar and space filled out. Below the sills, mortar is filled to make adequate space. A matching sill color can be painted to have a uniform decoration.

Replacing a window sill is not an easy feat. But don't worry, there are a lot of step-by-step guides available.

To replace a window sill, here are the things you will need:

  • Hammer
  • Putty knife
  • Adhesive gum
  • Utility knife
  • Drill
  • pry bar
  • Chisel
  • measuring tape
  • nails and screws
  • pencil, or marker, and paint.
  • Circular saw
  • Reciprocating saw
  • Sawhorses
  • Framing hammer (20-ounce straight claw)
  • Galvanized casing nails (#12 or #16)
  • Primer-sealer
  • Paintbrush

If you have all the things listed, you can now go on to replace your window sills.

Method One

Removing the old sill is to loosen it

Below are the Steps :

  • Step One – Loosen the Old Window Sill

The first step in removing the old sill is to loosen it. You can do this by using a knife to enlarge the distance and cut layers of paint and adhesive.

  • Step Two – Trim the Edges

The next thing you need to do after loosening the adhesives is to trim the edges to create a wider prying gap.

  • Step Three

When the distance is large enough, use the pry bar to close it. Don't forget to clean the surface. You sprayed to provide an even finish for your new window sill.

  • Step Four – Measure and Cut the Correct Size

This is the most critical step to repair the window sill. If your calculation is not accurate, you can waste a lot of resources. Measure the measurements carefully to prevent destroying your materials.

  • Step Five – Check if it Fits

The easiest way to do this is to overlap your window and trim it bit by bit to get the best fit you need. This is going to give you power over the thickness and the distance.

  • Step Six – Fix it

For this move, you can use nails to fix it. But, more conveniently, you can drill holes and use screws so that you can quickly remove or change in case of repair and replacement in the future.

Window sills are an essential part of home windows. Having them installed and maintained improves your home's overall value as it protects your abode's structural integrity. It also offers warmth and a worry-free feeling from any sudden changes in the weather.

Method Two

Replace A Window Sill with Cut the Sill in Half

  • Step 1 – Cut the Sill in Half

This is important to make the removal process easy. Next, change the circular saw so that the saw blade's width is the same as the saw blade's thickness. Start the cut on the outer edge and proceed to the window. Take the cut as far as space allows the saw to be turned. You're going to need another tool to finish the cut. The tool may be a saw, a hand saw, or a wood chisel. All in all, choose the tool that best fits your skill level and finish the cut.

  • Step 2 – Pull Half of the Sill Out one at a Time

It better you use a flat pry bar if you're not powerful enough to free each piece of board with your hands. Wear a decent heavy-duty pair of work gloves when you're trying. Take your time, and you're expected to be able to work each piece free of charge.

  • Step 3 – Pull the Nails out With a Vice Grip Tool

Set the jaws to the vice grips, but they barely bite into the nail. Next, close the jaws around the nail and work each nail loose slowly. Sometimes the nose of the lock pins may be used to apply leverage.

  • Step 4 – Determine the Original Sill's Exact Size

Determine the actual size from the two missing sections of the old sill. Don't forget to figure out the saw blade's thickness as you measure the blade's total length.

  • Step 5 – Cut a New Sill from Some Softwood Stock

Don't build up the wood to make your new sill, but instead, if possible, use one piece of stock. When moisture tends to be a big concern, use redwood, cypress, or cedar.

  • Step 6

Design the outer edge so that it is rounded.

  • Step 7

Sand the board thoroughly and paint with primer paint on each side and edge.

  • Step 8

Slide the new sill in place and nail it securely to the galvanized nails. Set each nail just a little bit below the surface and fill it with caulking. Often, caulk around the edges of the freshly installed sill.

  • Step 9

Paint a new sill with an exterior-grade paint finish.


The importance of window Sill in homes cannot be overemphasized as it brings beauty and design to the general outlook of a home. Following the above steps will guide you through the process of installing one in your home. It should be done considering the rules of right-sizing and fit, sealing, horizontal installation. Replacing a window Sill requires much time and equipment if you're to get it installed yourself.

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