French doors bring elegance and natural light to any home, but achieving historically accurate divided-light doors requires careful planning and skilled joinery. Whether you are restoring a period home or adding classic charm to a new build, custom-built French doors offer superior fit and authentic detailing that stock units cannot match. This article covers the essential techniques for designing, milling, assembling, and installing custom French doors with divided lights, drawing on traditional carpentry methods adapted for modern workshops. For advice on preparing the opening, see our guide on adding a door opening to an existing wall.
Design and Layout for Custom French Doors
Before cutting any wood, you must establish the overall dimensions, panel layout, and light configuration. French doors are typically installed in pairs, with each leaf measuring roughly half the width of the finished opening minus clearance. The design process starts with three key decisions.
Determining Door Dimensions and Proportions
The rough opening width and height dictate the door size. For a standard 36-inch-wide passage, each leaf of a pair measures about 17 3/4 inches, allowing 1/4 inch of clearance between doors and at the jambs. Historical proportion rules suggest a door height roughly 2.5 times its width, though 6-foot-8-inch and 7-foot heights are common in modern construction. When matching existing windows in a period home, align the door’s divided-light pattern with the window muntin spacing for visual consistency.
Divided-Light Layout and Glass Sizes
Divided-light doors feature individual panes of glass separated by muntins and stiles. The number of lights varies by architectural style. The table below shows common configurations.
| Style | Lights per Door | Typical Glass Size (in) | Muntin Width (in) |
|---|---|---|---|
| Greek Revival | 8 or 12 | 8 x 10 | 1 1/2 |
| Colonial | 6 or 9 | 10 x 12 | 1 1/4 |
| Victorian | 4 or 6 | 9 x 14 | 1 1/8 |
| Modern | 2 or 3 | 12 x 18 | 1 |
Once the light layout is drawn, calculate stile and rail widths. Exterior door stiles typically range from 4 to 6 inches wide, with bottom rails wider than top rails to resist sagging. Allow 1/4 inch of bite at each edge where glass meets the frame.
Material Selection for Durability and Appearance
Custom French doors demand stable, rot-resistant stock. The best choices include:
- Mahogany — Excellent stability, rot resistance, and clear finish. Ideal for exterior doors in wet climates.
- White Oak — Dense, durable, and takes stain well. Suitable for painted or clear finishes with proper sealing.
- Douglas Fir — Strong and affordable, with straight grain that paints beautifully. Common in period restoration.
- Cedar — Lightweight and naturally rot-resistant, though softer than oak or mahogany.
All stock should be milled from fully seasoned lumber (6 to 8 percent moisture content) and acclimated to the workshop for at least two weeks before joinery begins.
Milling and Joinery for Door Frames
The strength of a French door depends on the joinery connecting the stiles and rails. Traditional mortise-and-tenon joints remain the gold standard for custom work. Modern shops often supplement them with epoxy and mechanical fasteners for added durability.
Cutting Mortise-and-Tenon Joints
Each rail-to-stile connection uses a through tenon or a stub tenon. Through tenons, which extend fully through the stile, offer the greatest strength and are preferred for bottom rails. Follow this sequence:
- Cut the stiles to finished length plus 1/2 inch for trimming after assembly.
- Plow the tenon cheeks on the rail ends using a dado stack or tenoning jig. Tenon thickness should equal one-third the stock thickness.
- Chisel the mortises in the stile edges to match. For through tenons, chisel from both sides to prevent blowout.
- Dry-fit each joint and adjust for a snug, hand-tight fit. The joint should require light mallet pressure.
Milling Muntins for Divided Lights
Muntins form the grid that holds individual glass panes. Each muntin is a narrow piece with a rabbet cut to receive the glass. The intersection of horizontal and vertical muntins requires half-lap joints. Mill the muntin stock to the same thickness as the door but narrower, typically 1 to 1 1/2 inches wide. Cut the glass rabbet 3/8 inch deep by 3/8 inch wide to provide adequate bearing for the pane. Bore small vent holes at the bottom of each rabbet to allow moisture to escape, preventing seal failure.
Raising Panels for the Bottom Section
Many French door designs pair glazed lights above with raised panels below, typically one or two panels per door leaf. The raised panel is cut with a bevel around its perimeter so it fits into a groove plowed in the stiles and rails. Leave 1/4 inch of space around the panel to allow for seasonal expansion and contraction. Never glue the panel into the groove; use rubber setting blocks or small wedges to center it.
Glazing and Weatherproofing
Exterior French doors face constant exposure to sun, rain, and temperature swings. Proper glazing and weatherproofing ensure the doors perform for decades. The approach differs depending on whether you use traditional single glazing or modern insulated glass units.
Single-Glazing with Putty
For historic authenticity, single-pane glass set in glazing putty is the traditional method. The process is straightforward:
- Apply a thin bed of glazing compound in the rabbet.
- Press the glass pane into place and secure with glazing points every 6 to 8 inches.
- Roll out putty into ropes and press against the glass edge, then trim with a putty knife at a 45-degree angle.
- Allow the putty to cure for two to three weeks before painting.
Single glazing provides modest insulation, but the thin muntins and traditional appearance are unmatched for period restorations. Where energy codes require better performance, specify insulated glass units.
Insulated Glass Units with Simulated Dividers
For modern energy performance, order insulated glass units (IGUs) sized to fit each opening. Simulated divided lights use adhesive grilles applied to the glass surface, while true divided lights with grilles between the glass panes offer a more authentic look. The glass must be ordered before final milling so the rabbet dimensions match the IGU thickness exactly. Use neoprene setting blocks at the bottom and silicone sealant for weatherproofing. Install a dam at the bottom rail to prevent water from wicking into the joinery.
Weatherstripping and Threshold Seals
French doors have two meeting edges where weatherstripping is critical. Use silicone bulb weatherstrip in a routed groove along the meeting stile. At the bottom, a drip cap on the exterior face and an adjustable threshold with a compressible bulb seal prevent water intrusion. Install a rain drip kerf in the bottom rail to channel water away from the door bottom. For interior details on finishing the opening, see our door casing installation guide.
Hanging Hardware and Final Installation
Heavy French doors require robust hardware. Standard residential hinges are insufficient for the weight of glazed door leaves. The choice of hinges, handles, and closing hardware affects both function and appearance.
Selecting and Installing Hinges
Use three 4-inch by 4-inch ball-bearing butt hinges per door leaf, with the third hinge placed midway between the top and bottom hinges. Mortise each hinge flush with the door edge and jamb. For doors wider than 3 feet per leaf, use four hinges. Consider decorative wrought-steel or brass hinges for period-appropriate hardware that also provides the necessary load rating. Align the hinge pin center with the door face for proper swing clearance between the two leaves.
Locking Hardware and Handing
French doors typically use a mortise lock set on the active leaf, with flush bolts top and bottom on the inactive leaf. The flush bolts retract into the head jamb and threshold. Keyed locking on both leaves provides security but requires careful alignment. Choose a lockset rated for exterior use with a minimum 1-inch deadbolt throw. For advice on selecting quality entry door components, refer to our buyer’s guide.
Installation and Adjustment
Installation begins with a fully framed and flashed rough opening. Ensure the header is sized to carry the load above the opening; see our detailed guide on headers for window and door openings. Shim the hinge jamb perfectly plumb before hanging the doors. Adjust the reveals (the gap between door and jamb) to 1/8 inch on the hinge side and 1/8 to 3/16 inch on the latch side. After hanging, check for gaps at the meeting stiles and adjust the bevel on the latch edge as needed. A properly hung pair of French doors should open and close without binding, with an even gap of about 1/8 inch between the meeting stiles.
Before applying final finish, sand all surfaces through 120-grit, raise the grain with a damp cloth, and sand again at 150-grit. Apply two coats of exterior primer followed by two coats of high-quality exterior paint or marine-grade varnish. Pay special attention to end grain at the bottom of each stile, where moisture penetration is most likely. With careful joinery, proper glazing, and quality hardware, your custom French doors will serve the home for generations.