Dream Lands Design
You're here: Home » Home Improvement » How to Replace a Window Sill – Simple Step by Step Guide

How to Replace a Window Sill – Simple Step by Step Guide

The sills are being installed together with windows– this is the widely met common practice. However, sometimes due to general repair works in the house or desire to change the sill to fit into a new interior, people search for ways not to repair the window sills but to replace them.

image - How to Replace a Window Sill - Simple Step by Step Guide
How to Replace a Window Sill – Simple Step by Step Guide

In this article, we will review the reasons to change the window sill, what material to choose, and provide you with step by step guide how to replace a window sill.

Read Also:

Why Do We Replace Window Sills?

We live in a time of technological progress. This means that things change not only from the outside but also from the inside. The materials used now are made of better quality than before to serve for years.

A range of window sills availability is such huge now, that customers may easily find the solutions to create the aesthetic look, have good design, cope with all sorts of workload, and are at affordable prices.

The widely met reasons to replace a window sill are:

  • The current design is slightly damaged and the common general lovely look is lost. To repair the window sill is not a solution in this case.
  • The integrity of the product is violated, which may shortly lead to its total break;
  • It does not fit into the interior of the room, or we need the wider one to sit on, for example.

The material for the new window sill should be chosen considering the appearance of sills you like, the purpose they will serve for, and your budget.

There are different materials used to produce sills, but the most popular are plastic and wooden products, acrylic, and sills made of natural and artificial stone.

Every kind of material has unique advantages and disadvantages, but your choice will depend on the appearance and purposes the sills will serve for.

How to Replace Interior Window Sill

To replace a window sill is a very complicated task and demands good planning, specific tools, and experience.  This work is mainly done by technicians.

image - How to Replace Interior Window Sill

Let us review the basic steps Apex Window Werks specialists do to replace interior window sill:

  1. A technician should have a wide range of equipment needed to replace interior window sills including chisel, hacksaw, hammer drill, jigsaw, putty knife, respirator, and others;
  1. Dismantle of old construction. The most important is not to damage your walls, window glass while doing dismantle works.

To remove the wooden sill the specialist mainly needs a hacksaw, scrap, and hammer to hit it underneath the several times to make it move.

A specialist should wear a respirator to protect the lungs from dust all the time. There will be a need for a puncher and grinder to remove the concrete window sill.

The removal of this construction will be accompanied by a great amount of dust. Removing plastic sill is comparable quite an easy task compared to the two cases above.

Since it is fixed with the help of mounting foam, the technician may easily use a knife to cut through the foam.

  1. After an old structure has been removed the surface should be thoroughly prepared and cleaned to install the new one. All the dust, garbage, and foam residues must be taken away.
  1. Installation of a new window sill is a very complicated task.

Quick guide:

    • A very accurate size fitting guarantees not only the way the construction will look like but also its strength and functional abilities. The sill should not be hardly leaned on while doing exact dimensions to avoid its damage.

Wooden sills from sides are to be worked out with special antiseptic to avoid rotting and excessive moisture to get inside of the material.

    • It is necessary to make a cement screed if new construction is lower than the old one. There may also be some damages on the wall after dismantling works, which should also be removed with the help of a cement screed.
    • Silicone sealant is to be applied to the whole width of the window for the new construction to stick thoroughly avoiding the empty spaces. If not done properly, this will further lead to heat waste.
    • If necessary, special boards can be placed into the hole underneath the sill. They will serve as additional support for the sill to keep weight on.
    • Special horizontal “level stick” should be used all the time for the correct installation.
    • Use the mounting foam for a connection and filling in all the holes. A foam or cement screed should be used underneath the construction to fill all the empties there.
    • After all, work is done it is needed to give a sill a break for all the foam and screed to get still.
    • Before the final painting of the walls, fine sandpaper is to be used on the surface of the cement screed.


Having said all the above, to replace a window sill is a complicated task. It should be done considering the rules of right-sizing and fit, sealing, horizontal installation. This requires much time and equipment. We would like to make your life easier.

Apex Window Werks technicians are only one phone call away. Don’t have time or tools? – Get your sill replaced in one click.

Your Header Sidebar area is currently empty. Hurry up and add some widgets.