All You Need to Know About Doorway Casing


The trim around a door frame—also known as doorway casing—is installed first and foremost to conceal unsightly construction gaps left between the frame and the drywall. But while it minimizes seams in your home’s construction, the clean visual border around the door can also enhance the architectural beauty of any home. Whether you want to install new doorway molding or update your existing one, start with this guide to doorway casing.

Detailed Doorways

In new construction, one the most common types of doorway casing consists of three separate pieces: two long pieces for the sides of the door and one shorter piece (called “head casing”) for the top of the door. You’ll notice that the casing boards slope slightly, typically thicker on one edge than the other. The thinner edge will be installed toward the inside of the door frame to reduce bulk in the doorway, while the thicker outside edge matches the depth of the base trim to create a cohesive threshold.

When setting out to design doorway casing, homeowners will find a wide variety of options, from simple trim with a completely flat surface to more elaborate (and often wider) options with intricate moldings and protrusions. Two major considerations when finding a favorite style are joint choice and sizing.


All You Need to Know About Doorway Casing

Door Casing Materials

What you use to build doorway casing is just as important to your style (and your budget) as the joint design and trim width. For homeowners and homebuilders, the choice comes down to these types of casing.



Installing Door Casing

Looking to save some money on labor to invest more in the materials themselves? Lucky for you, any homeowner can install standard door casing with some simple instructions. The DIY carpentry task takes about 15 minutes per each side of the door, once you become familiar with the tools and technique.

MATERIALS AND TOOLS Available on Amazon – Power miter saw – 18gauge finish nailer – 1” and 2” finish nails – Carpenter’s wood glue

If you’re installing casing around one or two doors, consider renting an 18-gauge finish nailer and a power miter saw from a construction rental store (for a combined cost of about $60 per day). But if you plan to complete more extensive trim work, or if you’re an active handyman, you may opt to purchase the items instead. A decent consumer-grade power miter saw costs between $150 to $200 (view example on Amazon), while a finish nailer costs an additional $100 to $150 (view example on Amazon).

Before installing any type of casing, you’ll need to determine where, exactly, to place it along the doorframe. Measure and draw a line about ¼-inch from the inner part of the door frame; the line should be the same distance from the frame on the sides and the top of the door. This “reveal line” will serve as a guide for installing the inside edge of the casing. The quarter-inch of extra space is necessary to give the door hinges room to operate.

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Cutting and installing the casing will vary depending on your finished design.


Homeowners can create more elaborate door frames by adding multiple pieces of trim above the original casing board. The general rule of thumb with built-up head casing is to add progressively wider trim as you go upward on the wall. Virtually any trim can be layered to create the look you want; consider using chair rail, bed molding, or concave cove molding. Professional finish carpenters often use crown molding at the very top of a built-up head casing for a uniquely ornate look.