Replacing a window with a French door (double doors, often glass-paneled) is a popular renovation for opening a room to a backyard, deck, or balcony. The opening must be enlarged (window opening is usually narrower than French door rough opening), header re-sized, and the new threshold installed at floor level. Done well, the door operates smoothly and the wall reads as original. Done poorly, structural issues, drafts, or door alignment problems.

This guide covers replacing a typical 60×48 inch window with a 72×80 inch French door — the most common scenario.

Before you start

Three things to settle:

1. Engineering for new header. French door rough opening is wider than typical window — header must be sized for the new span. Engineer or BCIN designer for header design. Permit required for structural change.

2. Threshold at floor level. Window sill is typically 24-30 inches above floor. French door threshold is at floor level. Wall below the existing window must be removed: framing, insulation, drywall, exterior siding.

3. Permit + inspection mandatory. Cutting structural opening: building permit. Inspector verifies header, framing, and water sealing. Without permit: code violations and resale issues.

What you'll need

Tools

Reciprocating saw
Drill with bits and driver
Tape measure
Level (4-foot)
Pry bar
Caulk gun

Materials

French door (sized to new opening)
Header lumber (sized per engineer)
Jack studs and king studs
Threshold and weatherstripping
Flashing and house wrap (matching exterior)
Insulation
Trim (interior and exterior)
Construction screws and framing nails
Caulk (high-quality polyurethane)

Engineer-stamped drawings required for new header

Larger opening = larger header.

Wrong header sizing = visible sag, drywall cracks, structural risk.

Engineer-stamped drawings are required for the permit. The header size depends on the opening width and the load above it.

Step-by-step instructions

Plan opening dimensions and pull permit

French door rough opening: per door manufacturer's spec.

Header sized per engineer.

er sized per engineer.

Pull permit; engineer's drawings included.

Inspector verifies during work.

Build temporary shoring

Wall above window is currently supported by old window header.

When old header removed, ceiling above will sag.

Build temporary 2×4 wall ~4 ft from work area, floor-to-ceiling.

Carries load during opening expansion.

Remove existing window

Per standard window removal procedure.

Unscrew flange.

Pull window out from outside (or cut and remove from inside).

Cut wall below window to floor level

Mark expanded opening dimensions on wall.

Cut drywall, framing, sheathing along marks.

Remove wall material between old window and floor.

Verify no plumbing or electrical in path; reroute if needed.

Cut wall to required width

If new opening is wider than old: cut additional studs.

Header span limit per engineer (don't exceed).

Install new header

Header sized per engineer.

Install above new opening; supported by jack studs at each end.

Verify level.

Install jack and king studs

King studs full-height, framing the opening.

Jack studs from floor to bottom of header.

Per engineering.

Install French door

Lift door (heavy: 100-200+ lbs for typical French door).

Position in opening.

Anchor through mounting flanges into framing.

Verify level and plumb.

Door operates smoothly.

Install threshold and weatherstripping

Threshold at floor level.

Sealed to floor with backerod and caulk.

Weatherstripping around perimeter.

Install flashing and exterior trim

Flashing tucks under siding above; over door's top edge.

Side flashing and bottom drip edge.

Caulk all exterior joints.

Install interior trim and finish

Interior casing (jambs).

Threshold and rug or transition strip.

Caulk where casing meets wall.

Paint to match.

Insulation around perimeter

Spray foam (low expansion) or batt insulation in gap between door and rough opening.

Don't compress (over-foaming distorts door frame, racks operation).

Cover with trim.

Final inspection and test

Inspector verifies header, framing, flashing, weather seal.

Test door operation: open, close, lock.

Should swing smoothly and seal at threshold.

Common mistakes that cost you

Skipping engineer for header. Wrong header = sagging wall. Always engineer.
Skipping temporary shoring. Ceiling drops while opening expanded. Always shore.
Wrong threshold height. Door doesn't seal. Threshold flush with floor.
Inadequate flashing. Water enters wall around door. Multiple flashing courses required.
Skipping permit. Code violation; resale issue.

Frequently asked questions

What drives the cost of this conversion?

Several factors set the price: the door unit itself (style, glazing, and material — vinyl, wood, or fibreglass), the engineering for the new header, the City of Ottawa permit, and the construction labour if you hire it out.

Site conditions matter too — a load-bearing wall, electrical or plumbing in the opening, and exterior finish repairs all add scope. Ask for a detailed written breakdown so you can see exactly what each line covers before work begins.

Can the floor handle a French door (no extra weight or load)?

Yes — French door doesn't add structural load (window/door doesn't carry weight).

Concern is the wall above: header must support the wall and roof loads above.

Engineer confirms.

Does this require disturbing existing landscaping?

Possibly — if door opens onto deck or patio at existing level.

If no existing deck: install threshold, then plan deck or patio level (often higher than original yard for door clearance).

Plan landscape impact in design phase.

When to call us instead

Window-to-door conversions are popular for opening homes to outdoors. Our team handles design, engineering, permits, and execution.

Book a free 60-minute site visit →

Related Ottawa services

If you're considering a French door addition, our team handles the full scope. Book a free 60-minute consultation.