Exterior and Interior Window Casings
Provide the Finishing Touches to a Window
By Mark J. Donovan
Window casings offer a number of unique benefits to a window and home. Exterior
window casings provide an accent piece around the window and act as a transition
piece between the window and the house siding. Interior window casings help to
cover the transition where drywall abuts the window frame, and function as
insulation barriers to outside air drafts. Interior window casings also serve to
dress up and provide the finishing touches to a window. Often interior window
casings are installed that complement the baseboard trim, crown molding and
other finish carpentry in a room or home.
And in some window casing styles, in particular when window sills are included,
they offer functionality. Interior window casings also enable a surface area for
securing window treatments.
Installing Window Casings
Instead of purchasing pre-fabricated window casings with the windows you can
alternatively install your own window casings around your new windows.
Installing window casings is actually not that difficult, however, I highly
recommend the use of a miter saw.
Interior window casings come in a variety of materials and styles. The most
inexpensive interior window casing moldings are made from plastic, MDF and pine
wood. More expensive interior window casings are fabricated out of hardwoods or
exotic woods. Colonial casing is very commonly used in trimming out interior
window frames, however flat 1x 3 or 1x4 trim lumber is also commonly used.
Most window casing installations involve using mitered 45 degree cuts, however
straight cuts (butt cuts) are also used, particularly when flat 1xN trim
lumber is used.
As part of every interior window casing installation project there are side, top
and bottom (apron) pieces that must be installed. In many cases finish
carpenters and homeowners also elect to use window stool to create a window
sill. On the apron piece, the edges are usually tapered inwards 15 to 22.5
degrees, or they are mitered at a 45 degree angle and corresponding small return
pieces are installed on each end.
Pre-primed 1x4 wood or Azek PVC trim lumber is often used for exterior window
If using wood exterior trim you may want to consider encasing the window
casing pieces in aluminum prior to installing them around the window frame
to protect them from ultra-violet and water damage. Also, it is important
that flashing be installed over the exterior window casing to ensure water
does not penetrate behind the window casing, windows and siding.
Often when you order the installation of windows they include window casings
and extension jambs. Window extension jambs are used commonly for 2x6 wall
framing. They effectively extend the window jamb of the standard 2x4
manufactured window frame to the width of the 2x6 framed wall.
Photo by Mark Donovan
Finishing Window Casings
Window casings can be finished in a number of different ways. They can be
simply primed and painted for example. Alternatively they can be stained and
then polyurethaned. Regardless of how you plan to finish the window casings, I
highly recommended pre-priming/painting/staining the window casing prior to
cutting and installing it on the window frame. In addition, after each cut, dab
the cut ends with paint or stain to hide any seams.
For information on
Installing a New Window, see the
Installing a New Window Ebook from
HomeAdditionPlus.com. The Installing a New Window Ebook provides easy to
understand, step-by-step instructions, on how to remove an old window and
install a new one. Pictures are included for every key step in the process.
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