Installing new door trim is one of the most effective ways to freshen up a room without spending a lot of money. It covers the rough gap between the drywall and the door frame while adding a clean decorative element to your living space. This project is perfect for homeowners who want to improve their carpentry skills.
To install door trim, you must measure the door jamb accurately, cut the moulding at precise 45-degree angles using a miter saw, secure the pieces with finishing nails, and fill gaps with caulk for a smooth appearance. This guide breaks down every step to help you achieve a result that looks like it was done by a master carpenter.
Choosing the Right Trim Style for Your Home
The first step in this project is selecting the right material and style. Your choice should match the architecture of your house. If you have a modern home, simple flat stock trim works best. For older or traditional homes, colonial or fluted casings are popular choices.
You also need to decide on the material. Solid wood is durable and great for staining, but it can be expensive. Medium density fiberboard, or MDF, is a common choice because it is affordable and comes pre-primed, making it easy to paint. However, MDF can swell if it gets wet, so avoid using it in bathrooms with high humidity.
Consider the width of the trim as well. Wider trim often looks more luxurious and can hide more imperfections in the wall. Standard casing is usually about two and a quarter inches wide, but three-inch or wider options are becoming very trendy. Make sure the scale of the trim fits the height of your ceilings and the size of your doors.
| Trim Material | Best Used For | Cost Level |
|---|---|---|
| Solid Pine | Staining or painting; durable finishes | Moderate |
| MDF (Composite) | Painted finishes; dry areas | Low |
| Hardwood (Oak/Maple) | Staining to show grain; high traffic | High |
| PVC / Vinyl | Bathrooms or exteriors; moisture prone areas | Moderate to High |
When buying your materials, always purchase about 10 percent more than you think you need. This accounts for cutting mistakes or defects in the wood. It is much better to have a little extra leftover than to run back to the store in the middle of your work.
Essential Tools and Safety Gear
Having the right tools makes the difference between a frustrating afternoon and a successful project. You do not need a shop full of expensive equipment, but a few key power tools will speed up the process. A miter saw is the most important tool for this job because it creates the angled cuts needed for the corners.
A pneumatic nail gun is another game changer. While you can use a hammer and nail set, a nail gun shoots thin nails that leave tiny holes. This saves you energy and prevents accidental hammer marks on your new wood. If you do not own these tools, you can often rent them from local hardware stores.
- Tape Measure: Get one that is easy to read for precise measurements.
- Miter Saw: Essential for cutting sharp 45-degree angles.
- 18-Gauge Brad Nailer: Perfect for holding trim without splitting thin wood.
- Utility Knife: Use this to cut old caulk or trim shims.
- Wood Glue: Critical for keeping corner joints tight over time.
Safety is vital when working with power saws and flying debris. Always wear safety glasses to protect your eyes from wood dust and metal fragments. Ear protection is also smart because saws and nail guns are loud enough to damage your hearing over time.
“Invest in good safety gear before buying fancy tools. Your eyes and ears are irreplaceable, and a simple pair of safety glasses is the most valuable tool in your kit.”
Make sure you have a clear workspace. You need enough room to swing long pieces of lumber around without hitting walls or furniture. Set up your saw on a stable table or stand so the wood stays flat while you cut.
Measuring and Marking the Reveal
The secret to professional looking door trim is the “reveal.” The reveal is a small strip of the door jamb that stays visible between the edge of the jamb and the new trim. You should not install the trim flush with the inside edge of the jamb because the door hinges need clearance to operate smoothly.
A standard reveal is about 3/16 of an inch. To mark this, set your combination square to 3/16 of an inch. Place it against the inside edge of the door jamb and make pencil marks at the top corners and roughly every foot down the sides. These marks will guide exactly where you place your trim pieces.
Measuring the length comes next. Measure from the floor up to the pencil mark you made on the head jamb (the top part of the frame). Do this for both the left and right sides of the door. Floors are rarely perfectly level, so the left leg of your trim might need to be a slightly different length than the right leg.
Write these measurements down clearly. Many pros write the measurement directly on the wall where the trim will go so they do not mix up the pieces. This simple habit prevents cutting the wrong board and wasting expensive material.
Cutting and Installing the Side Casings
Start with the side pieces, often called the legs. Set your miter saw to a zero-degree angle to cut the bottom of the trim flat so it sits on the floor. If you have carpet, you might need to keep the trim slightly off the subfloor, but for hardwood or tile, it should rest right on top.
Next, cut the top of the side pieces at a 45-degree angle. The direction of the cut matters. The inside edge (the shorter side of the angle) should match the measurement you took from the floor to the reveal mark. Always cut a little long if you are unsure; you can trim more off, but you cannot add wood back.
According to experts at Family Handyman, fitting the joints perfectly requires patience and sometimes slight adjustments to the saw angle if your door frame is not perfectly square. Test the fit by holding the piece up to the wall against your reveal marks.
Apply a bead of wood glue to the top mitered edge before you nail anything. This glue helps bond the side pieces to the top piece later, preventing the joint from opening up as humidity changes in your home. Tack the trim in place with your nail gun, placing nails every 12 to 16 inches. Do not drive the nails all the way into the corners yet; leave the top loose until you fit the head casing.
Fitting the Head Casing
The head casing is the horizontal piece that goes across the top of the door. This piece needs a 45-degree cut on both ends. The short side of the trim (the bottom edge) should equal the distance between the inside edges of your two side pieces installed on the wall.
Cutting this piece requires precision. Ideally, the angles of the head casing and the side casings should meet perfectly to form a tight 90-degree corner. If you have a scrap piece of wood, test your cuts first to ensure your saw is cutting true.
Once cut, apply glue to the mitered ends. Slot the head casing into place between the two side pieces. Adjust the corners until they are flush. If the drywall sticks out too much and prevents the corner from closing, you can place a small shim behind the trim to push it out slightly.
Secure the corners by nailing through the side of the trim into the jamb. For extra strength, some carpenters drive a nail horizontally through the corner of the side casing into the head casing. This technique, called cross-nailing, locks the joint tight. Wipe away any excess glue immediately with a damp cloth.
Finishing Touches for a Polished Look
The installation is done, but the job is not finished until you prep the wood for paint or stain. Even with the best measuring, you will likely have small nail holes and tiny gaps at the joints. This is normal and easy to fix.
Use a high-quality wood filler for the nail holes. Overfill them slightly because the filler shrinks when it dries. Once dry, sand the filler smooth with fine-grit sandpaper. For the corners, if there is a small gap, rub a little filler in there too to hide the line.
Caulking is the next critical step. You need to caulk the long edge where the trim meets the wall and the edge where the trim meets the door jamb. This hides shadows and gaps caused by uneven walls. Use a paintable acrylic latex caulk. Cut the tip of the tube small and move the gun steadily to create a smooth bead.
For painting, This Old House recommends using a sash brush, which has angled bristles that make it easier to cut in straight lines. Semi-gloss or high-gloss paint is the standard for trim because it stands out against flat wall paint and is easier to clean. Apply long, smooth strokes and let the paint dry fully between coats.
Common Mistakes to Avoid
One common mistake is forcing the trim to follow a wavy wall. Trim is somewhat flexible, but if the wall is very uneven, nailing the trim tight into a depression will cause the mitered corners to pop open. Instead, let the trim bridge the gap and fill the space behind it with caulk.
Another error is using nails that are too long. Standard 2-inch nails are usually fine, but if you have pocket doors or electrical wires running close to the jamb, long nails can cause serious damage. Always be aware of what is behind the wall.
Finally, avoid rushing the sanding process. Rough wood grain or uneven filler will show through the paint. Run your hand over the trim before you pick up a paintbrush. If you feel a bump, the paint will highlight it. Take the time to make it smooth like glass.
Conclusion
Installing door trim adds a refined touch to any home and is a manageable project for DIY enthusiasts. By measuring carefully, cutting precise angles, and finishing with patience, you can transform a plain doorway into a stunning architectural feature. Share your renovation success on social media with hashtags like #DIYHomeImprovement, #CarpentrySkills, and #HomeRenovation. We would love to hear about your experience in the comments below!
Disclaimer: This article is for informational purposes only. Working with power tools and home construction involves risks. Always follow manufacturer safety instructions and local building codes. If you are unsure about any step, consult a professional carpenter.
