How to Install Casing on One Side of an Exterior Door Like a Pro | Step-by-Step Guide

Category - Casing, Baseboard, and Shoe

Skill Level - 1

Casing is a type of trim or molding that frames the sides and top of interior and exterior doorways, as well as windows, to cover the gap between the wall and the door or window frame. It serves both a functional and aesthetic purpose, acting as a visual transition that helps define the style of a room or exterior façade, while also concealing the rough edges of the wall opening and any space that may exist between the door frame and the wall itself. Casings can vary in design, width, and detail, ranging from simple, clean lines to more elaborate, decorative profiles, allowing for customization according to the architectural style of the home or building.

In new construction projects, it is a common practice to install exterior doors during the framing stage of the building process. This early installation is crucial for several reasons: it secures the property against unauthorized entry, provides a means for temperature control within the construction site, and helps maintain a more stable environment conducive to ongoing construction activities.

At this stage, a "bang door" is typically used in place of the final door slab. A bang door is a temporary door slab installed within the exterior door frame. The use of bang doors is strategic; they are intended to withstand the rigors of construction, protecting the site without risking damage to the final, more expensive, and often more aesthetically pleasing finish door slab.

Once the construction process is nearing completion, and the risk of damage from construction activities is reduced, the bang door is removed and replaced with the finish door slab. This approach ensures that the final door remains pristine and undamaged, reflecting the intended architectural and design choices without the wear and tear of the construction process.

If the finish slab is available, it should be installed on the door jamb before casing the interior side of the door. It is common that the bang door is slightly different than the finish slab and minor adjustments must be made to ensure that the finish slab will function properly.

Tools Needed

Tape measure Miter saw

Nail gun (18 gauge) Hand tools

Supplies Needed

Nails (1-3/4" 18 gauge) Wood glue

Wood filler or putty Sandpaper (120 grit)

Primer Paint

Material Needed

Casing

MDF, poplar, alder, oak, maple

Quality Check Criteria

Exterior door opens and closes properly, latching closed if door knob is installed

Miters/joints glued, puttied and sanded smooth, primed if needed

Casing is tight against the drywall and the door jamb without movement

Process to Install Door Casing

Preparation

Inspect Door Operation: Before starting, open and close the door several times to ensure it operates smoothly with consistent reveals around all edges. Adjust the door hinges if necessary to achieve proper alignment.

Prepare the Work Area: Remove any drywall overlapping the door jamb using a utility knife and hammer. Ensure the jamb surface is flush and ready for casing installation.

Measuring and Cutting

Mark Casing Reveal Lines: Using a pencil, mark out the reveal lines on the door jamb. The standard reveal is typically 1/8" to 1/4" from the edge of the jamb.

Cut Side Casings: Measure and cut two pieces of casing approximately 2-3 inches longer than needed for the door sides. Cleanly cut the bottom ends that will meet the floor.

Mark and Cut for Fit: Position the casing pieces against the jamb, aligning with the reveal marks. Mark the top end where the casing will be cut at a 45-degree angle for the miter joint. Cut the casing at this mark.

Install Side Casings: Nail the casing pieces to the door jamb and the wall, ensuring they sit tightly against both surfaces. Use a finish nailer for a clean installation.

Installing the Header

Measure and Cut the Header: Measure the distance from the outside to the outside of the two side casing pieces. Cut a header piece about 1/16" longer than this measurement with 45-degree angles on both ends for the miter joints.

Test and Adjust Fit: Dry-fit the header piece above the door, making adjustments as necessary to ensure a tight, seamless fit with the side casings.

Glue and Nail the Header: Apply wood glue to the miter joints, then nail the header in place, ensuring a tight fit against both the wall and the side casings.

Finishing Touches

Fill and Sand: Fill all nail holes and joints with wood filler or putty. Once dry, sand smooth for a seamless appearance.

Touch-up Paint/Stain: Apply paint or stain to match the existing finish, covering any filled areas or blemishes for a cohesive look.

Inspection and Cleanup

Check for Gaps: Ensure there are no visible gaps in the casing joints or between the casing and the wall/door jamb.

Operate the Door: Open and close the door to confirm that the installation of the casing has not impacted its operation.

Efficiency Tips

Batch Work for Efficiency: With experience, learn to measure and cut multiple pieces at a time. This batching process can significantly improve efficiency and reduce the total time spent on installation.

Final Notes

Always wear appropriate personal protective equipment (PPE) when operating saws and other tools.

Ensure all cuts are precise, and double-check measurements before cutting to minimize waste.

Regularly maintain tools to keep them in good working condition, ensuring clean cuts and safe operation.