Fine Homebuilding Project Guides

Finish & Trim Carpentry

How-To

Precision Window Trim

This systematic approach to cutting and assembling window casing ensures better joints and a faster installation.

By Anthony Vitale Issue 281 – Feb/Mar 2019

Synopsis: Finish carpenter Anthony Vitale explains his approach to window and door casing. He starts with tips for repairing window and door jambs so they won’t complicate the trimwork, including the window trim. He then details the production of the casing, including tips for efficiency when cutting and gluing (which he does on a table to guarantee the joints will come out right) and a step by step process for assembly.

Somewhere along the way, we’ve decided that it’s the apprentice’s job to run base or to find and mark studs. There’s nothing really wrong with that, but I also like to throw window and door casing into the mix. The skills required to case an opening are fundamental to finish carpentry, and the conditions are pretty similar from one opening to the next. Learning how to case from the get-go teaches you prep; detailing; nailing pattern; understanding the difference between level, plumb, and straight; and how to set and sight reveals. You’ve got 12 different tools you’re going to use to get through the process.

The method I teach apprentices started somewhat out of frustration. Various factors can throw off miter joints when you stick-build a casing around an opening, and it can take a lot of time and effort to get the joints right. Throw a junior carpenter into the mix and the results aren’t always great. But that’s not the case with bench building. Doing the assembly work on a tabletop takes the irregularities of an opening out of the equation and makes the process simple enough that anybody on the crew can do it. That frees up senior carpenters from having to micromanage and troubleshoot, and makes it easy to scale up for big jobs.

Openings need work

Window and door jambs tend to get banged up and dirty during construction, and we need to clean and repair them so they don’t compromise and complicate the trimwork we’re installing. Although not comprehensive, the photos shown here reflect some of the most common fixes we make when working our way through a house.

Joints getting levered closed, and nailed off. — **Fix the jambs.** Lever joints closed, and nail them off. Glue down chips, then sand them flat. Chips and open joints will show in the finished opening and must be fixed while fully accessible.

Using a wallboard saw to cut back drywall around a window — **Reestablish the gap.** Use a wallboard saw to cut back the drywall around the window, which frees up the jambs so that they have room to be nudged into proper alignment if necessary.

Using a chisel to scrape errant drywall compound — **Scrape it down.** Clean up any errant drywall compound with a scraper or chisel, taking care not to damage the jamb. Skip this, and the trim won’t make continuous contact with the jamb.

Using a sander across the faces of the jambs to get a clean surface and to flush up the corners; window trim — **Sand out imperfections.** Keeping the sander flat, sand across the faces of the jambs to get a clean surface and to flush up the corners. Sanding takes you down to clean wood and ensures a more consistent finish.

A compact router and a roundover bit adding a slight roundover on jamb edges; window trim — **Round it over.** Jamb edges often show dings, and even if they don’t, a sharp edge doesn’t hold paint as well as a slight roundover, which can be added with a compact router and a 1⁄8-in. roundover bit.

sandpaper being used to finish off the inside corners of the jambs, matching the router bit’s radius; window trim — **Ease the corners.** Use 150-grit sandpaper to finish off the inside corners of the jambs, matching the router bit’s radius where the router can’t reach.

Develop a production mindset

Keeping the tape measure in your tool bag and marking stock in place eliminates read and transfer errors. Once you’ve measured the opening and cut the stock to rough lengths, put the tape away. For rough sizing, I like to cut stock about a foot longer than the opening—or even more than that with wider casing. That sounds like a lot, but with this 4-in.-wide casing, it really only leaves 4 in. of wiggle room once you subtract the 4 in. for each miter. I want my crew to be methodical about rough sizing, but I don’t want them to lose time doing it. The critical accuracy comes when marking the stock in place on the opening and cutting to those lines.

A quick tip on getting the most out of your stock: Cut the long lengths first (usually door legs and larger openings), and use the cutoffs from those for smaller openings. That way, you’re not chopping down 16-footers for 3-ft. windows and can use your cutoffs a bit more efficiently.

When casing a whole house, a lot of the efficiency comes from using production methods. That generally means doing one task with one tool— say, cutting all of the miters for all of the casing in a room or floor of the house—before moving on to the next step in the process. This cuts down on setup and adjustments, and you don’t have to keep track of 10 different tools at once.

marking combination square for finished casing; window trim — **Mark reveals.** Set a combination square to 3/16 in., and mark reveals at each corner. Even on stain-grade work, the resulting crosshairs will get hidden behind the finished casing.

labeling piece for placement on window; window trim — **Mark in place.** Transfer the marked reveals to the stock, and label each piece to indicate its place on the opening—top, bottom, left, and right—and the opening it belongs to.

Cutting all of the left-hand miters; window trim — **Kiss the line.** Cut all of the left-hand miters, then swing the saw to 45° the other way to cut all of the rights. Take most of the line to ensure that the finished casing will hide the reveal marks.

Aligning a biscuit joiner to a common spot on the casing; window trim — **Cut the slots.** Align a biscuit joiner to a common spot on the casing, aiming to keep the biscuits close to the short point of the miter, which is the more vulnerable to opening up. Register the joiner to the show side of the casing when possible to aid in keeping the faces of the intersecting pieces in plane.

Glue it up, set it aside

cleaning up materials at the ready; window trim — **Set the stage.** Arrange all of the parts in their proper position, stage biscuits and clamps at each corner, and have glue and cleanup materials at the ready.

Have a bucket of clean water, a rag, and a toothbrush at the ready to clean up squeeze-out. I like to use Titebond II for casing joinery. Clam Clamps are my go-to for mitered casing joints because their multiple grab points lock the casing together in three dimensions, allowing me to move the glue-up as soon as it’s assembled and make room on the table for the next. Pinch clamps just don’t have the same grab and stability, especially not on wide casing. As each casing is completed, set it against its opening to dry out and fully cure, which takes about a day. Don’t rush this; the joints should be completely set up prior to final sanding and fastening them in place. Assemble the casing on a large flat table or workbench. I have a handful of these lightweight torsion-box benchtops that sit on sawhorses.

smearing glue around with a finger; window trim — **Don’t starve.** Squeeze glue into the biscuit slot and onto the face of one side of the miter, insert a #20 biscuit, and smear the glue around with a finger. There should be plenty to coat the other workpiece.

pushing miters tight by hand; window trim — **Assemble and clamp.** Starting at the head and going one at a time, assemble each joint flat on the bench, aligning the corners and pushing the miters tight by hand while tightening the clamp.

A damp rag removing squeeze-out from the back of the joint and from the table — **Clean the joint.** After clamping a miter, use a clean, damp rag to remove the squeeze-out from the face and back of the joint and from the table. Rinse the rag in a bucket between joints.

Brush the profiles. Use a damp toothbrush to remove glue from the profile, wiping the brush clean on a damp rag frequently.

a few taps with a soft-faced hammer — **Bottoms in.** Because the legs are already locked in, both of the bottom joints must be assembled at the same time. A few taps with a soft-faced hammer help with positioning.

Photos by Matthew Millham.

More about installing window casings:

Fine Homebuilding Recommended Products

Fine Homebuilding receives a commission for items purchased through links on this site, including Amazon Associates and other affiliate advertising programs.

A House Needs to Breathe...Or Does It?: An Introduction to Building Science

Allison Bailes is great at explaining complex building science topics in simple terms that anyone can understand. If your goal is a new house or remodel that embodies the best practices that building scientists have to offer, buy this book right away.

Buy at Amazon

Homebody: A Guide to Creating Spaces You Never Want to Leave

Joanna Gaines may have started as a celebrity designer on HGTV, but she’s proven to be the real deal. This book help you understand how and why good design works so that you can recreate it on your own.

Buy at Amazon

Get Your House Right: Architectural Elements to Use & Avoid

If you are designing or remodeling a traditional home and want to make sure that you get all the finish details right, this book is for you. Marianne’s drawings are illustrative, covering every aspect of interior and exterior finishes.

Buy at Amazon

View PDF

Previous: Making Mitered Window Casing Next: Trimming a Window on a Paneled Wainscot Wall

View Comments

LauraWilliams | Jan 15, 2019 05:04am | #1
Good Work!!
DeweyMessier | Jan 16, 2019 02:55am | #2
Really Appreciated!!
BenjaminShaw | Jan 17, 2019 05:28am | #3
Very good
KevinHuggins | Jan 25, 2019 03:18am | #4
Good!
jeffwoodwork | Feb 20, 2019 03:39pm | #5
Where are you finding finger joined popular case?
RonaldTague | Mar 08, 2019 02:11am | #6
I appreciate your work
JohnMartin12 | Mar 09, 2019 03:35am | #7
Excellent!
WesleyParks | Mar 15, 2019 07:59am | #8
great
JohnPrice6 | May 15, 2019 03:56am | #9
well done!
ArmandLewis | May 16, 2019 12:55am | #10
super work