Kitchen extension glazing in 2026: bifolds, sliders, Crittall and rooflights compared

Bifold doors fold concertina-style to one side, leaving up to 90% of the opening clear. Standard configurations: 2-panel (1.8–2.2m), 3-panel (2.7–3.3m), 4-panel (3.6–4.4m), 5-panel (4.5–5.5m), 6-panel (5.4–6.6m). London kitchen extensions typically specify 3 or 4 panels.

Cost (2026 prices, supply and install): aluminium powder-coated, mid-range thermal break (1.2 W/m²K), standard hardware — 3-panel £4,500–£6,500; 4-panel £6,000–£8,500. Premium brands (Reynaers SL38, Schueco ASS70) £8,000–£15,000 for 4-panel.

Pros: large open aperture, well-understood install, good thermal performance, no winter draft issues with quality units. Cons: visible mullions when closed (6–8 vertical lines), folded panels stack to one side reducing usable wall space, hardware has more moving parts than other options.

Sliders run on tracks, with two, three or four panels overlapping. Configuration delivers wide single open aperture with minimal mullions. Pocket-slider variants slide fully into a wall pocket leaving completely flush opening.

Cost (2026 prices, supply and install): 2-panel aluminium £6,000–£9,000; 3-panel £9,000–£14,000; 4-panel £14,000–£20,000. Premium slim-frame brands (IDSystems Theedge, Sky-Frame, Cero) £18,000–£35,000 for 4-panel.

Pros: minimal frame visible (some slim-frame profiles 25mm visible mullion), large uninterrupted glass area, contemporary aesthetic, can deliver thermal performance to 0.8 W/m²K. Cons: maximum opening is roughly half the total width (slider parks behind fixed panel), heavier panels need quality hardware, higher cost per linear metre than bifolds.

Steel-framed glazing in distinctive thin black mullions — originally Crittall brand, now also Fabco, Mondrian, IQ Glass and others. Internal screens and external doors available in matching styles.

Cost (2026 prices, supply and install): per linear metre £3,000–£5,500 depending on system, panel size and complexity. A 3.5m steel-framed bifold or slider runs £12,000–£20,000.

Pros: distinctive aesthetic with strong design appeal, slim mullions create grid pattern, durable, thermally upgraded modern versions (1.2 W/m²K achievable). Cons: highest cost per linear metre of any option, premium aesthetic only fits some property styles, longer lead times (10–14 weeks vs 5–7 for aluminium).

Almost every London kitchen extension specifies overhead glazing to bring sky-light into the new space. Two principal options: flat rooflights (single pane of glass on a frame, set into the flat roof) and roof lanterns (pyramidal multi-pane structure projecting above roof level).

Flat rooflights: cost £1,400–£3,500 each depending on size (typical 1.0×1.5m to 1.5×2.5m). 2–3 typically specified per kitchen extension. Clean, contemporary aesthetic, simple roof detail.

Roof lanterns: cost £3,500–£8,500 for typical 1.8×2.4m unit. Distinctive raised feature element, draws light from multiple angles, more visible architectural statement.

Both add roughly £4,000–£10,000 to the total extension budget when fully specified. We design daylight using ray-tracing software during design phase to confirm placement and number deliver the target daylight factor.

If your budget is £75–110k for the extension and you want maximum opening for indoor-outdoor flow: 3 or 4-panel aluminium bifold + 1 lantern or 2 rooflights. Total glazing £10–15k. Best-value standard kitchen extension package.

If your budget is £110–160k and you want minimal visible frame and contemporary aesthetic: 3 or 4-panel premium aluminium slider + lantern + 2 rooflights. Total glazing £18–28k. Sharper aesthetic.

If your budget is £160k+ and you want a distinctive design statement: steel-framed Crittall fixed and opening panels, integrated with internal Crittall screens, plus minimal-frame rooflights. Total glazing £35–55k. High-end kitchen extension finish.

We design and supply through three preferred suppliers (IDSystems, Express Bifolds, Sunflex) with backup options for specialist brands. Never subcontracted to the cheapest installer.