Master leaf and slave leaf
A pair of French doors is not two identical doors. One leaf, the master, carries the handle and the multi-point lock, and this is the leaf you use day to day. The other, the slave leaf, usually stays closed and is secured independently by shootbolts, typically operated by a small lever or espagnolette handle on its inner face, that drive into the head and threshold.
Both leaves can be opened when you need the full width, for moving furniture or letting a lot of air through, but the slave leaf's bolts need releasing first.
Shootbolt locking, not just a latch
The slave leaf's security doesn't come from a single bolt but from shootbolts firing into both the top and bottom of the frame, which is what stops the leaf being levered or kicked at the meeting point where the two doors close together. On the master leaf, a multi-point lock similarly drives hooks or rollers into keeps up the full height of the frame when the handle is lifted and the key turned.
Cylinder choice matters here too: a TS007 3 star rated cylinder resists snapping and drilling far better than a basic euro cylinder, and it's a sensible upgrade on any French door pair.
Which way should they open
Outward opening is the more common choice on French doors because it keeps the full room floor space clear and doesn't compete with furniture placed near the door. Inward opening suits properties where there's limited outside clearance, a narrow path or a step straight off a patio, but you need to plan the room layout around the swing.
Either way, the opening direction should be decided before the order goes in; it isn't something that's easily changed afterwards.
Thresholds and accessibility
A standard low threshold gives a small upstand for weather performance, which is fine for most households. Where step free access matters, a level access threshold can be specified, though it needs a little more attention to drainage and detailing outside to stop water tracking in.
Side panels and glazing
French doors are often flanked by one or two fixed glazed side panels, which let you widen the overall opening for light without adding another moving leaf. These panels are glazed the same as the doors, typically a double glazed unit with a low-E coating and warm edge spacer, and can be toughened or laminated where they sit close to floor level for safety compliance.
| Component | What it does |
|---|---|
| Master leaf | Carries the main multi-point lock and daily use handle |
| Slave leaf | Secured by top and bottom shootbolts, normally stays closed |
| Side panel | Fixed glazed unit widening the opening without a moving leaf |
| Threshold | Low upstand as standard, level access available on request |
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Frame material and weathertightness
A French door frame is built from the same chambered uPVC or composite profile as the rest of the range, with steel reinforcement run through the sections that take the most load, typically the hinge side of each leaf and the frame head. Where the two leaves meet in the middle, a matching weatherseal on both edges closes the gap against driving rain, and this junction is worth checking is properly compressed when the doors are closed, since it's the one seal on the set that isn't backed by a continuous frame.
Drainage channels built into the outer frame let any water that does get past the seals run back out rather than pooling at the bottom, which matters more on French doors than a single door simply because there are two meeting edges rather than one.
Glazing spec and Building Regulations
French doors fitted as a replacement or in a new opening need to meet Part L of the Building Regulations for thermal performance, which in practice means a double glazed unit with a low-E coating, an argon fill and a warm edge spacer as standard, rather than an older style aluminium spacer that conducts heat away at the edge of the glass. Triple glazing is available where a lower U-value is wanted, though it adds weight to each leaf and is worth discussing at survey if that's a priority.
Where a French door sits within a low level glazed area, such as a full height side panel, the relevant panes also need to meet the safety glazing requirements of Part K, which normally means toughened or laminated glass rather than standard float glass.
Who tends to choose French doors
We see French doors chosen most often by homeowners replacing a single back door or tired patio doors on an older extension, where the appeal is as much about how the opening looks from inside the room as the practical width of the opening itself. First time buyers doing up a period property also gravitate toward French doors for the traditional look, while anyone short on floor space in front of the doors, inside or out, is usually better served by sliding patio doors instead.
What's included at £1,499
Our French doors start from £1,499 fully fitted, which covers the door pair, glazing, standard hardware and installation. Colour, glazing spec and side panels can move that figure, and we'll walk through exactly what's included at the survey stage rather than leaving it vague on paper.