Installing wainscoting protects your walls while adding old-world charm. Installing wainscoting on a wall with no windows or doors is fairly straightforward. When you come to a wall with windows then the task is more challenging but is still something you can do with some patience and know-how.
Remove the Trim
Before installing the wainscoting use a pry bar to lift trim and remove it from around the window. Pry gently to avoid damaging this trim since you will be reinstalling it. You may want to mark each piece so that you know which side of the window it came from.
Fit the Wainscoting
Where the wainscoting meets the sill, notch the back of the sill so that you can slide the panel behind it. A hacksaw with an offset handle makes this cut easier.
Install the Wainscoting
Measure the cuts that need to be made to fit the wainscoting around the window and mark these on the panel. Then cut it out with a jigsaw or table saw. Dry fit it up to the window. Do any trimming or planning necessary since a window can be out-of-plumb, especially in an older home. Apply glue to the panel and then nail the wainscoting to the wall.
Measure the Trim
Measure the thickness of your wainscoting and compare it to the thickness of your trim. For instance, if your trim thickness is 3/4 inches and your wainscoting is only 1/2 inch thick then you can install the panels and the trim will still be above the face of the wainscoting. Doing a dry fit will help you to decide what alterations you need to make.
Install the Trim
If you need to increase the thickness of the trim you can do this by placing boards behind the trim as filler strips. This will bring the window trim out more so it sits on top of the wainscoting. Nail boards with the thickness desired across the top and sides of the window opening. Then reinstall the trim on top. You may have to use a thin line of caulking to hide any seam between the boards. This assumes you are painting the trim instead of staining it. You can also purchase new trim in the thickness desired.
Reinstall the Sill
Now put the sill back in place. You may need to trim the sill to make it a perfect fit. Attach it with nails. Fill in any new nail holes in the trim and touch up the paint. The rest of the wainscoting installation will be a breeze once you have tackled applying it around a window.