French Door Glass Sealed Unit

The replacement unit engineered specifically for French door apertures. A 28mm symmetric toughened double-glazed sealed unit (4mm toughened / 20mm argon cavity / 4mm toughened) sized for single-leaf French door panels — 600 to 900mm wide, 2050mm tall — with both faces toughened to BS EN 12150 to satisfy the Approved Document N critical-location requirement that applies to all door glazing below 1500mm.

French doors are functionally different from patio doors: each leaf is a narrow single panel hinged at the side, opening outward (or inward) from a fixed frame, typically used as garden access from a living room or as a balcony door from a bedroom. The aperture geometry is narrow-and-tall (typically 3:1 ratio), and replacement units therefore need a different stock-size set from the wide-and-tall patio doors. This flagship handles the French-door-specific size range.

Why symmetric, not asymmetric

For French doors, symmetric 4-20-4 toughened construction is the cost-optimal correct spec for the typical residential application. Asymmetric stacks (e.g. 6mm outer / 4mm inner) add weight without meaningful safety or acoustic benefit at this aperture size. Acoustic-laminated outer is an upgrade for properties facing busy streets — covered as a configurator option — but for the default garden-access French door, symmetric toughened is the right call.

Both faces toughened means the unit satisfies critical-location requirements on both sides — important because French doors are routinely impacted from both directions (pets, children pushing the door, knocks during furniture moves). Single-face toughening leaves the non-toughened side as the safety weak point.

Technical specification

Where this unit is the right call

• Replacement of failed (misted, blown, water-ingressed) sealed units in existing French doors — PVCu, aluminium, or timber. The frame is usually fine; only the unit needs replacing.
• Garden-access French doors from living rooms and kitchens — the standard UK domestic application. Symmetric toughened DG is the spec building inspectors expect.
• Bedroom-balcony French doors at first-floor level — where fall-from-height risk is mitigated by the Juliet-balustrade on the outside. The internal door glazing still needs critical-location safety glass.
• Period-property French door replacement in Victorian / Edwardian terraces where original doors have been removed and modern frames fitted — this unit replaces the modern unit, not the original glazing.
• Boutique commercial settings — small hotels, restaurants, cafes with French-door street frontage where the door glazing has failed.

For full-height patio and bi-fold doors (1500-2700mm wide), the Patio / Bi-Fold Door Glass Unit (Triple Glazed) flagship is the right spec. For composite door inserts (small panels in a solid composite door), see the Composite Door Glass Insert flagship. For French doors where overhead-glazing safety applies (rare — typically a fanlight above), specify the laminated variant in the configurator.

Stock sizes — French-door-specific

Four UK-standard French-door stock sizes are listed below — all 2050mm tall to match the standard UK domestic French-door panel height:

• 600 × 2050 mm — narrow French door (cottages, smaller terraces)
• 700 × 2050 mm — standard small French door leaf
• 800 × 2050 mm — most common French door leaf size
• 900 × 2050 mm — wider French door (modern PVCu, aluminium systems)

Dispatch 10-14 working days from order (toughening adds ~3 days vs the standard clear unit). Custom sizes — including doors with internal Georgian bar overlays, arched-top fanlight units, and bespoke heritage-replica fielded-pane builds — are priced via the online glass configurator.

Delivery: French door units at these dimensions fit standard pallet networks (5-7 day delivery) but require careful packaging — every order ships on a timber A-frame within a protective cardboard sleeve. Inspection on receipt before installer signs off is critical; toughened-pane chip damage in transit can develop into spontaneous breakage weeks later.

Certification and standards

Every unit ships with: UKCA mark, BS EN 1279 Declaration of Performance, BS EN 12150 toughening stamp permanently etched in corners of both panes (visible at the rebate after fitting — hold a phone torch at low angle to find it), BS EN 12600 Class 1(C)1 impact certificate, and a critical-location compliance statement on request. Heat-soak testing (BS EN 14179) is available as an order option — useful for properties with previously-experienced spontaneous breakage of nearby toughened units.

Frequently asked questions

Do I definitely need toughened both faces?

Yes for compliance. Approved Document N requires that critical-location glazing (which all door glazing below 1500mm is) meets Class 1(C)1 or equivalent on the face that's accessible to impact. Both inside and outside faces of a French door are accessible. Building Control inspectors checking a notifiable installation will look at both sides. Specifying toughened both faces is the only compliant build for a replacement French-door unit.

Will it fit my existing French door rebate?

Most modern PVCu, aluminium, and timber French doors are designed for 24-28mm units. Send the existing unit thickness (gentle measurement at the corner where the seal is exposed) plus a frame profile photo to our contact form for compatibility confirmation. The most common rebate mismatch is between older 20mm-rebate doors (designed for thinner units) and the 28mm standard — those typically need re-rebating or unit downgrade to 24mm.

Acoustic — busy road frontage?

Rw of this symmetric build is ~30 dB — modest. For French doors on busy streets (Inner London terraces, town-centre cottages), specify the asymmetric-acoustic variant in the configurator: 8.8mm acoustic-laminated outer + 4mm toughened inner takes Rw to ~38-40 dB. The PVB laminate also satisfies the critical-location requirement on the outer face, so safety + acoustic stack in one build.

Low-E upgrade — worth it?

For garden-facing French doors that are open frequently in summer and well-shaded in winter, the U-value upgrade matters less. For north-facing or shaded French doors that stay closed most of the year, hard-coat low-E (Pilkington K) drops centre-pane U to ~1.2 W/m²K — adds ~£15-25 to a typical 800 × 2050 unit. Hard-coat is essential because soft-coat planitherm doesn't survive the 620°C toughening temperature.

Internal Georgian bars — possible?

Yes — internal Georgian bars (clip-on overlay bars inside and outside the unit with a matching spacer-bar grid inside the cavity) are configurable. For French doors with traditional fielded-glass aesthetics, specify the bar layout (typically 4-panel or 6-panel) at order. Lead time extends to ~14-21 working days.

Toughened stamp — where is it?

Etched permanently on each pane, typically 20-30mm from one corner. Visible inside the rebate after fitting — hold a phone torch at a low angle to find it. The stamp reads "TOUGHENED / BS EN 12150 / [manufacturer code]". No stamp = not toughened — important to verify on delivery as the unit can't be reverse-checked once fitted.

Warranty?

10 years on edge-seal integrity (BS EN 1279-2). 10 years on argon retention to ≥80% of initial fill. Toughened pane integrity is manufacturer-lifetime warranty against in-stock defects; spontaneous NiS-inclusion breakage is excluded unless heat-soak testing is specified at order. Transit damage is covered for 14 days from delivery — photograph on receipt before signing off.