How to Install Interior French Doors: Step-by-Step Guide with Tools and Troubleshooting

Installing interior french doors is one of the most impactful single-day upgrades a homeowner can make, but two things stop most DIYers before they start: not knowing what to prepare for, and not knowing what to do when something goes wrong mid-installation. This guide covers both. From choosing the right door type to fixing the four most common problems, every step is here in the order you need it.

Before You Start: Prehung vs Slab French Doors

The first decision you make before buying determines how the entire installation goes. Prehung and slab french doors look similar on a spec sheet but require completely different levels of preparation, skill, and time. Getting this wrong means either buying more door than you need or setting yourself up for a much harder job than expected.

What Is a Prehung French Door?

A prehung french door unit comes with the door panels already mounted on hinges inside a complete jamb assembly. The frame, hinges, and door stop are pre-attached and arrive as a single unit ready to drop into a prepared rough opening. For most interior installations, prehung is the faster and more forgiving option because the frame is already square and the hinge positions are already set.

What Is a Slab French Door?

A slab french door is the door panel only, with no frame or hinges included. Slab installation requires an existing jamb in good structural condition, precise mortising of hinge locations, and careful alignment of both panels so they meet evenly at the center. The skill requirement is noticeably higher than prehung, and small measurement errors compound quickly across a double-door installation.

Which Is Right for Your Project?

Use this table to match your situation to the right door type before purchasing:

For the majority of interior french door installations, prehung is the right choice. It costs more upfront but saves time, reduces the margin for error, and produces a more consistent result. Slab installation is worth considering only when the existing jamb is perfectly plumb and square and replacing it would cause unnecessary wall damage.

Shopping for interior french doors? Browse the Interior French Door Collection at Doors and Beyond - prehung units available in a range of glass styles, finishes, and sizes. Not sure what size you need? Read the Interior French Door Sizes Guide before ordering.

Tools and Materials: What You Need Before You Begin

Having everything on hand before you start prevents the most common reason installations stall midway. A mid-project hardware run costs time and breaks workflow. Run through this list the day before installation.

Every item in this list serves a specific function at a specific step. The 4-ft level is the most critical tool on this list, one that is too short will not catch an out-of-plumb opening, which is the root cause of most interior french door problems after installation.

How to Prepare the Rough Opening

The quality of your rough opening determines everything that follows. A level, plumb, and square opening makes each subsequent step straightforward. A flawed opening creates compounding problems at every stage. Invest time here and the rest of the installation moves quickly.

Step 1 – Remove the Existing Door and Frame (~30 min)

Score the caulk or paint line where the casing meets the wall using a utility knife before prying — this prevents the drywall from tearing when the casing is pulled. Work through the removal in this order:

• Remove casing on both sides of the opening, labeling each piece if you plan to reuse it

• Pull the existing jamb by working a pry bar between the jamb and the jack stud

• Inspect the jack studs and header for rot, damage, or previous water intrusion before proceeding

Step 2 – Check for Level, Plumb, and Square (~20 min)

Place your 4-ft level on the floor across the full width of the opening and note any slope. A slope of more than 1/4 inch will cause the doors to swing open or closed on their own after installation. Then check the following:

• Hold the level vertically against each jack stud to confirm plumb

• Measure diagonally from corner to corner in both directions — equal measurements confirm a square opening

• A diagonal difference of more than 1/4 inch requires correction before you proceed

Step 3 – Verify and Adjust the Rough Opening Size (~30 min)

Standard rough opening for interior french doors is the door unit width plus 2 inches (1 inch per side for shimming) and the door unit height plus 2.5 inches. Verify your opening matches these dimensions, then address any issues:

• Opening too wide: add a strip of lumber to the jack stud to reduce the gap

• Opening too narrow: trimming the jack stud is structural work that may require professional assessment

• Opening correct: proceed directly to setting the door unit

How to Install Prehung Interior French Doors

With a prepared opening, prehung installation moves faster than most homeowners expect. The key is working methodically from the hinge side first and checking level at each shim point before driving any nails. Nail placement cannot be easily undone once the jamb is secured.

Step 4 – Set the Door Unit in the Opening (~20 min)

With a second person assisting, lift the prehung unit into the rough opening and center it side to side. Before shimming, confirm two things:

• The threshold sits level — if the floor has a minor slope, place a shim under the low side of the unit now

• The jamb faces are flush with the wall surface on both sides — note any discrepancy before installing casing

Step 5 – Shim and Secure the Hinge Side First (~30 min)

The hinge side is the anchor point for the entire installation. Slide cedar shim pairs behind the jamb at each hinge location, then work through the following sequence:

• Adjust shims until the hinge-side jamb reads plumb on the 4-ft level from top to bottom

• Drive one 8d finish nail through the jamb and shims at each hinge location, leaving the nail head slightly proud

• Recheck plumb after each nail before driving the next — do not skip this step

Step 6 – Shim the Latch Side and Check the Gap (~30 min)

Open both door panels and examine the gap between the door edges and the head jamb. The gap should be consistent and between 1/8 inch and 3/16 inch across the full top of both panels. Shim the latch-side jamb until the gap is even, then close both panels and verify they meet cleanly at the center. A gap that is tight at the top and wide at the bottom indicates the jamb is not plumb — adjust the shims before continuing.

Step 7 – Nail Through the Jamb and Trim Shims (~20 min)

Once both sides are plumb, the head is level, and door gaps are consistent, complete the fastening in this order:

• Drive finish nails through all remaining shim locations

• Use a nail set to countersink all nail heads below the surface

• Score shims flush with the jamb face using a utility knife, then snap them off, do not use a saw, as vibration can shift the jamb before nails fully set

• Fill nail holes with paintable wood filler, allow to dry, and sand smooth

>>> See more: How to Secure French Doors: Essential Tips for a Safer Home

Installing Hardware and Trim

Hardware and trim are where the installation shifts from functional to finished. Take the same methodical approach here and the doors will look professionally installed from both sides.

Step 8 – Install Door Handles and Lock Set (~20 min)

Interior french doors typically use passage sets (no lock) or privacy sets (push-button lock). Install in this sequence:

• Insert the latch mechanism into the pre-drilled hole on each panel

• Attach the handle or knob on both faces per the manufacturer's instructions

• Test the latch action fully before installing the strike plate

• Mark the strike plate position by pressing the latch against the jamb to leave an impression, then mortise and secure

Step 9 – Install Astragal or Door Stop (~15 min)

The astragal seals the gap between the two panels when closed. On most prehung units it is pre-attached, but if field installation is required, attach it to the inactive panel with the provided screws, positioned so it overlaps the active panel by 3/8 inch when both doors are closed. Install a floor or wall-mounted door stop to prevent the panels from swinging too far open and stressing the hinges.

Step 10 – Apply Casing Trim on Both Sides (~45 min)

Measure and miter casing trim to fit on both faces of the wall. Mark a consistent reveal of 3/16 inch back from the jamb face before nailing, then work in this order:

• Install the head casing first, then fit the two side casings against it

• Nail through the casing into the jamb every 16 inches and into the jack stud at each stud location

• Set all nail heads, fill, and sand before painting or staining to match surrounding trim

Need door hardware for your installation? Doors and Beyond carries European hinges, magnetic locks, and interior lever sets compatible with standard interior french door configurations.

Troubleshooting Common Interior French Door Problems

Even careful installations run into issues. These are the four most common problems encountered when installing interior french doors and the specific fix for each.

Door Swings Open or Closed on Its Own

This is caused by an unlevel floor or an out-of-plumb hinge-side jamb. Remove the hinge-side casing, loosen the jamb nails at the problem area, re-shim to plumb, and re-nail. For minor floor slopes under 1/4 inch, shifting the top hinge 1/16 inch toward the door stop can counteract the pull without reframing.

Gap at the Center Seam When Doors Are Closed

An uneven center gap means one or both panels are not hanging plumb, or the astragal is mispositioned. Check both panels with a level held against the door face. If one panel tilts, shim behind the hinge leaf with thin cardboard to adjust the angle. If both panels are plumb, reposition the astragal to bridge the gap evenly.

Door Rubs Against the Frame or Floor

Tighten all hinge screws first, a loose hinge causes the door to sag and drag against the frame or floor. If rubbing persists, use a hand plane to remove material from the rubbing edge in 1/32-inch passes. Never remove more than 1/8 inch total without re-examining jamb alignment.

Doors Do Not Latch Together Properly

Check that all hinge screws on both panels are fully tight. If panels still do not meet evenly, loosen the latch-side jamb nails, adjust shims until panels align when closed, and re-nail. Adjust the strike plate in 1/16-inch increments until the latch engages cleanly.

>>> See more: How to Install a Pocket Door: A Step-by-Step Beginner& Guide

DIY vs Professional Installation – How to Decide

Most interior french door installations are well within the reach of a confident DIYer. But specific situations make professional installation the smarter choice, and identifying those situations before you start saves time, money, and frustration.

When DIY Makes Sense

DIY is the right call when the rough opening already exists and is close to the correct size, the floor and walls are reasonably level and plumb, and you have basic carpentry experience with door installation or similar framing work. A prehung interior french door in a standard 60-inch or 72-inch rough opening is achievable in a single day for a homeowner comfortable with a level and a drill.

When to Call a Professional

Professional installation makes more sense when the rough opening does not exist and framing work is required, when walls are out of plumb by more than 1/2 inch over the door height, when the subfloor slopes more than 1/2 inch across the opening, or when the existing wall is load-bearing and the header requires structural engineering.

What Professional Installation Typically Costs

Professional labor for interior french door installation in the US ranges from $500 to $1,500 depending on the complexity of the opening, local labor rates, and whether framing work is required. For a standard prehung replacement in an existing opening, most installers charge between $500 and $800 for labor alone, not including the cost of the door unit.

Conclusion

Installing interior french doors comes down to preparation and patience at each step. Measure the rough opening accurately, choose prehung for most installations, shim the hinge side first, and address any fit issues before driving final nails. Follow the troubleshooting section if something feels off before moving to the next step. Done in the right order, this is a project most homeowners complete in a single day with lasting results.