How To Install A Window Sill

Having finally had our guest bedroom window replaced a few weeks ago (it now has the stained glass, too), finishing off the rest of the wall around the opening is well overdue.

We absolutely love our new window, but at the moment the area around the window is still just a mess.

The plan is to add a window sill as well as an architrave like there would have originally been around the window when the house was first built.

We are trying to replace as many missing period features in our home as possible and installing trim around the window is definitely a feature we’re keen to reinstate.

It’s one of the last jobs needed to be able to completely call this room finished, so we’re really excited to get it installed and painted!

The first step in finishing off the window is to install a new window sill. Obviously, we removed the horrible plastic coverings and windowsill when having the new window installed, but that’s basically just left a mess of dusty, dirty and crumbly plaster and brick.

This is what you will need:

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• Window sill – To make our lives easier (and because we don’t own a router) we decided to buy ready made timber window sills. The sill is basically a piece of timber that comes in different widths and already has a rounded edge.
• Cordless Drill & Drill Bits
• Jigsaw
• Wall plugs and screws
• Liquid Nails
• Sandpaper
• Paint (and possibly primer)
• Caulk
• Cardboard
• Scissors & Pencil

This how to install a window sill:

1. Preparations

Clean the area and remove any dirt, rubble and lose bits of plaster.

2. Make a template

We used a few pieces of old cardboard to make a cutting template.

We already decided on the depth of the window sill when we bought it, so really just had to work out where to place the cuts. Using a piece of cardboard as a template makes it easier to work out how and where you have to cut the window sill and minimised the risk of making a mistake on the actual piece of wood.

3. Cut your window sill

Using your template, mark the cutting lines on your window sill. Double-check your measurements and then use a jigsaw (or a normal handsaw if you don’t have one) to cut out the necessary corners.

Test to see if it fits and trim and sand as necessary.

4. Install the window sill

We used a combination of No Nails adhesive and screws to attach the window sill.

After double-checking that the sill fits and double-checking that it is level (ours wasn’t so we added a few strips of thin wood underneath to even things out) mark your drill locations and prepare a wall plug for the screw.

Next, apply some liquid nails and then drill your window sill into place. In our case, our edges aren’t perfect, but it wasn’t too important, as we are having the walls around the window and window sill skimmed, so any gaps will be covered.

5. Finish

After installing the window sill, all that’s left to do is fill the holes, sand, caulk and paint everything. In our case, we’re waiting until the wall is plastered and the architrave is installed, but it’s already a huge improvement.

Having a window sill already makes the window feel much more finished and even the room feels more complete than ever before. Now, all we need is for the plasterer to turn up!

Have you ever installed a window sill? Do you also find that it’s sometimes those little finishing touches that make everything come together?