French Door Rough Openings Done Right

When installing French doors, having an accurately sized rough opening is crucial for proper operation and aesthetic appeal. The rough opening refers to the initial hole cut into the wall framing where the pre-hung door unit will be positioned. If the measurements are off even by small fractions, you may end up with doors that bind, gap open, or fail to function smoothly.

With the right tools and techniques for calculating, laying out, and verifying the opening, you can avoid headaches down the road.

Measurements Needed

Accurately sizing the rough opening starts with gathering some key measurements:

• The door unit size - width and height
• Wall thickness where the opening will be located
• Required clearance space around the door frame perimeter
• Framing dimensions - header, king studs, bottom plate, etc.

Having these measurements allows you to use a standard formula to calculate the exact dimensions of the opening. Most pre-hung French door units have the sizes labeled, but double check this spec. The most common widths are 36 and 60 inches, while heights frequently are 80 or 96 inches.

Accounting for Clearances

When sizing the rough opening, you need to account for clearances around the door unit to allow room for shimming and squaring of the frame. The typical clearances are:

• 1/2 to 3/4 inch along the sides
• 1/2 to 3/4 inch along the top
• 1/2 inch clearance at the bottom

Factor these reveal measurements into your calculations. Insufficient clearances can prevent proper door operation.

Calculating the Rough Opening

The basic formula for sizing a rough opening is:

• Rough Opening = Door Unit Size + 2x Wall Thickness + 2x Side Clearances + Top Clearance

For example, if you are installing a 36" x 96" door with 5/8" clearance spaces into an exterior wall with 2x6 framing:

• Door Unit Width: 36 inches
• 2 x Wall Thickness: 2 x 6 = 12 inches
• 2 x Side Clearances: 2 x 0.75 = 1.5 inches
• Top Clearance: 0.75 inches

Calculating: 36 + 12 + 1.5 + 0.75 = 50.25 inches

Round up to the nearest 1/2 inch increment = 50 1/2 inches wide

Perform the same calculations for the height. Rounding your openings helps account for variances in plumb and level.

Adjustments for Finishes

If interior wall finishes like drywall will be installed, make sure to account for their thickness in the rough opening width and height:

• Drywall Thickness: 0.5 inches
• New Width: 50.5 inches + (2 x 0.5 inch Drywall) = 51.5 inches

Framing the Rough Opening

Once calculated, the next step is framing in the rough opening into the wall. This involves properly sizing and installing the main components:

• Header: Top horizontal framing member spanning the width of the opening.
• King studs: Vertical studs running floor to ceiling on each side of the opening.
• Jack studs: Vertical studs placed between the king studs and opening to support the header.
• Bottom plate: Horizontal board along the bottom of the opening.

Shim Spacing

When framing, make sure to position shims between each king stud and jack stud at both corners. The shims create adjustment space when squaring and fastening the door frame. Use 0.25-0.5" thick shims.

Verifying the Rough Opening

With framing complete, double check your work using the following best practices:

• Level - Use a 4+ foot level to verify floor and header are level.
• Plumb - Check king studs with level for perfect vertical plumb.
• Square - Measure diagonals to ensure frame is square (adjusted with shims).
• Test fit - Temporarily fit door unit with shims to test opening size.

Make any necessary adjustments before moving onto next steps. ACCURATE open sizes prevent binding doors that fail to operate and latch properly.

Preparing the Rough Opening

With framing completed and opening sizes triple checked, prep the rough opening using best practices:

• Install adhesive foam or rubber sill pan flashing across entire bottom of opening.
• Caulk seams between framing members with exterior sealant.
• Insulate between king studs and exterior wall sheathing.

Take your time with this vital prep work to prevent moisture issues after French door installation.

Hidden Shims

For added strength, position concealed shims on the back side of jack studs. They provide reinforced fastening points for frame mounting screws.

Installing Doors in the Opening

With pre-hung French door units, installation into the rough opening involves:

• Fitting the frame into opening
• Anchoring hinges into framing
• Securing jambs with shims/screws
• Confirming smooth operation

We recommend a minimum of 4 reinforced screws through door frame hinge jamb directly into framed opening. This provides superior strength and stability. Carefully shim and adjust frame until proper reveals are achieved and door opens/latches correctly.

Checking Spacing

As doors are anchored, open and close them to verify consistent spacing between doors and jambs. Adjust shims until the reveal is even across entire opening. Consistent spacing = proper installation.

Finishing Touches

The final steps for flawless French door rough openings involve:

• Caulking perimeter between door stops and framed opening.
• Installing interior trim pieces with finish nails - frame in openings..
• Applying protective finish - paint, stain, etc.

Take time with the finishing process for clean, professional results. Proper caulking essential for draft and moisture protection.

Troubleshooting Problems

Some common French door installation issues related to inaccurate rough opening sizes include:

• Gaps - If reveal space is uneven, air/water leaks result.
• Binding - Doors rub and catch on frame if opening is too tight.
• Levels - Doors sag if header not level with bottom plate.
• Plumb - Doors fail to latch evenly if king studs are not perfectly straight.

Carefully follow the steps above to prevent these problems. Making adjustments early is much simpler!

Maintaining French Doors

To keep French doors functioning smoothly for years, be sure to:

• Lubricate hardware components annually.
• Inspect weatherstripping for wear, replace as needed.
• Clean and protect door finish from elements.

Properly installed and cared for French doors should provide homeowners with decades of reliable performance.

Achieving accurate French door rough opening sizes is essential for proper installation and operation. Carefully calculating the width, height, framing, and clearances will ensure your doors function smoothly while enhancing your home's aesthetics.

We hope this detailed walkthrough gives you confidence to tackle your French door project. Precision planning and workmanship is key. With the right techniques, you can avoid frustrations and enjoy beautiful new doors for years to come.