How to Install Window Trim

Installing window trim is easy

Installing window trim is easy

Installing window trim (and door trim) is an easy way to give your home a distinguishing touch. Replacing existing trim is a simple job that’ll take just a little time to complete.

SkilToolsTips for Installing Window Trim

Whether you’re replacing an old window in a renovation or installing one into new construction, once the window is in and level, it needs to be framed. Before you install window trim, also called casing, make sure it matches the interior trim of your home’s doors — likewise with the exterior. Installing window trim is similar to installing door trim except for a few minor differences:

  • Unlike doors, you’ll likely have casing around the entire perimeter of your window. When this isn’t the case, you’ll have an apron and a stool for your window.
  • Of those previously mentioned pieces, the apron and the stool are the most easily confused. The stool is usually rounded and slightly thicker than the apron. You’ll nail the stool to the rough sill and place the apron as a finishing piece beneath the stool.
  • Use finishing nails or casing nails and a pneumatic nail gun instead of a drill/driver or hammer to attach the pieces. There is less surface area on the head of finishing nails, and they are much easier to hide with paint or stain.

Tips for Installing Door Trim

Almost everything you do when you install window trim you’d do when installing door trim.

  • For beveled trim, pay close attention to joints to make sure they are neat and square.
  • Try not to over-nail the casing, as splitting becomes more likely the more you nail. Depending on the length of each piece of casing, six nails per length should suffice — two at the top, two in middle and two at the bottom, alternating from the jamb side to the outer edge of the casing.
  • Don’t be discouraged if all your nails aren’t exactly flush on the first try; you can go back over them with a nail to alter their depth ( go about 1/8″ below the surface of the casing).


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