How to Put Wood Trim on a Window

To put the finishing touches on interior window trim, you need only a few tools - but also a plan. There are several styles to pick from; we'll take a look at the most popular.

Difficulty: Moderate

Instructions

Things You'll Need:

• Finish Nails
• Measuring Tapes
• Utility Knives
• Combination Squares
• Hammers
• Miter Saws
• Hammers

Getting Ready

1. Choose the style of window trim - there are many available. Check photos from the Internet or magazines, or at home improvement centers and lumberyards (the best way).

2. Take your ideas to the dealer along with measurements for each window (top and sides to be trimmed).

3. Pick a style for your trim's corners. Styles include butted casing (the side casing is butted straight into the bottom edge of the top casing), blocked casing (the top and side casing are butted into decorative blocks), mitered casing (the upper corners of the trim meet in a 45-degree angle).

4. Set up a work area - such as a bench at a comfortable height - with plenty of light.

5. Gather your tools: hammer, finish nails, tape measure, combination square, miterbox saw.

6. Remember that in almost all styles of trim a 1/4-inch reveal line is left around the perimeter of the facing edge of the window jamb. All casing is attached along this line and measurements are taken from here.

7. Mark you reveal by setting a 1/4-inch measurement in your combination square and use it as a guide to pencil in a light line on the edge of the jamb.

Butted Casing

8. Remember that butted casing is probably the simplest and easiest to work with. Here's how:

9. Cut a piece of trim slightly longer than the side of your window. Get the exact measurement by holding the piece directly against the reveal line already penciled on the window jamb. Mark the trim.

10. Use the miterbox saw to make a straight cut at your measurement.

11. Use the same technique to make a piece of trim for the opposite side.

12. Tack these pieces in place on the reveal lines marked on the window jamb - use just a couple of nails for now.

13. Cut a piece of trim slightly longer than the distance between the outside edges of your side trim pieces.

14. Hold this piece in place making sure one side is flush with the edge of the outside edge of the side trim. Mark the other side and cut on the miterbox saw.

15. Nail this piece in place. If you are happy with the results, now secure the trim to the window casing. Countersink all nail heads using a nail set. (Pre-drilling nail holes in the trim will help prevent any splitting.)

16. Fill nail holes with wood putty, and paint or stain to suit your decor.

Blocked Casing and Mitered Casing

17. Choose blocked or mitered casing, and install them this way:

18. Use corner blocks when applying blocked casing - these are decorative squares of wood that are placed in the upper corners of the window jamb. The lower inside corner of these blocks usually sits where the side and top reveal lines intersect.

19. Nail the corner blocks in place. (Pre-drilling nail holes in the trim will help prevent any splitting.)

20. Make side and top rails by first cutting pieces slightly longer than the measurements between the corner blocks for the top and between the corner blocks and the windowsill for the sides. Then place them against the wall and use a utility knife to make exact measurements.

21. Nail in place with one or two nails and make sure you are happy with the fit. Once you like the way things look, nail everything securely and countersink all nails with a nail set.

22. Fill nail holes with wood putty, and stain or paint to suit your decor.

23. Install mitered trim this way:

24. Make a few practice pieces on these mitered cuts (angled corner cuts) - once you get the hang of it you'll have little trouble doing tightly seemed corner joints.

25. Make the top piece of trim. Cut a 45-degree angle on a piece of trim (making sure that the edge that rests on your reveal line is the short point of the cut).

26. Place the piece of trim against the casing on the reveal line with the short point of the cut on the side reveal line. Mark the point where the trim crosses the reveal line on the opposite side. Cut on your mark, again making sure that the edge where you marked will be the short point of the angle.

27. Use a couple of nails to hold it in place at the reveal line.

28. Measure from the windowsill to the long point of the angle on the top piece of trim. Add about 1/2 to 3/4 of an inch to your measurement and cut a piece of trim square on both ends. Place this piece in place on the windowsill and then mark it with a utility knife where it meets the inside point of the top piece of trim.

29. Cut with a miter saw so that your mark is the short point of the angle. Fit it to the window casing. Once the fit is satisfactory, nail it in place with one or two nails. (Pre-drilling nail holes in trim will help prevent splitting.)

30. Repeat the process on the other side. Finish securing the trim with more nails once you are happy with the fit. Countersink all nails with a nail set.

31. Fill holes with wood putty, and paint or stain to suit your decor.

Tips & Warnings

• You must allow for a fairly large amount of waste with miter cuts - be mindful of that when you buy materials.
• It is a good idea to make a few practice joints to get the feel of the techniques.