Install external French doors.

External French doors — two leaves opening outward from a central meeting stile — are the classic British patio door. They give an unobstructed central opening that hinged single doors can't match, and they cost a third less than bi-folds. Expect to pay £900–£3,800 fitted in the UK for a standard 1.5–1.8m opening.

What Does the Work Involve?

Installing French doors means measuring the structural opening, ordering a frame-and-door set as a single unit, removing the existing door or window (or knocking out brickwork if widening), fitting a new lintel if needed, bedding the frame in plumb and square, mechanically fixing through the jambs and head, foaming the perimeter, fitting the door slabs, hanging them on their hinges, fitting the multi-point lock to the active leaf, fitting the shoot-bolts to the inactive leaf, dressing the threshold, and silicone-sealing inside and out.

Typical Costs

How Long Does It Take?

Like-for-like replacement is a one-day job. Converting a window to French doors takes 2–3 days including making good the brickwork, plastering and decoration. Lead times for ordering are 4–8 weeks depending on material and finish.

DIY or Professional?

Professional. A 1.8m double-door set must be plumbed within ±2 mm or the active leaf binds at the meeting stile. The threshold needs careful dressing to prevent driving rain ingress, and a structural opening change needs a building inspector. Use a FENSA or Certass registered installer.

Choosing the Right Tradesperson

Check FENSA or Certass membership. Ask which brand they fit and request U-value certification. Insist on a deep-rebate cill with under-cill drainage and a thermal break in aluminium frames. Get the warranty in writing — 10 years on the frame is normal. Look for 3-star Sold Secure cylinder on the locking leaf.

UK Regulations

Replacement doors must meet Part L (U-value ≤1.4 W/m²K). New openings need Building Regs approval for the structural lintel — this is notifiable separately. Glazing within 800mm of the floor must be safety glass to BS 6206 (Approved Document Part K). FENSA or Certass registration handles the door notification.

Common Problems

• Meeting stile gap: Frame twist of 3 mm or more leaves a light gap at the top or bottom of the central join. Re-shimming the frame fixes it.
• Threshold leaks: Wind-driven rain pools at the cill if the threshold isn't dressed with under-cill drainage holes.
• Slab sagging: Heavy aluminium or hardwood leaves drop on their hinges over time — quality installers fit three or four roller hinges, not two flag hinges.
• Shoot-bolt failure: The inactive leaf relies on shoot-bolts top and bottom; cheap units use plastic strikes that crack after 5 years.

Frequently Asked Questions