Bifold and Sliding Doors for London Extensions: What to Choose and What to Budget
Large glazed openings connecting the kitchen or living space to the rear garden have become the signature feature of the modern London extension. Bifold and sliding doors are the two dominant systems — but they are genuinely different products with different strengths. This guide helps you choose and budget correctly.
Bifold Doors
Bifold doors concertina open, folding flat against one or both sides of the opening. The panels hang from a track at the top (and sometimes a bottom track as well) and pivot on hinges so they stack alongside each other when open.
The practical reality of bifolds:
- When fully open, they create a genuinely unobstructed opening — the threshold is clear
- The folded panel stack takes up space at the side when open (typically 100–200mm per panel)
- Bifolds with a bottom track require a slight threshold step — frameless threshold bifolds are available but more expensive
- A panel width of approximately 700–900mm per leaf is standard; more than 8 leaves becomes unwieldy
- In London's compact rear gardens, bifolds that stack to one side allow the full width of the opening to be accessed — good for furniture movement and for a seamless indoor-outdoor feel
Strengths of bifolds:
- Maximum aperture when open — the entire opening is unobstructed
- Strong visual statement when closed — large pane-to-frame ratio on quality systems
- Familiar system — most London homeowners understand what they get
Weaknesses of bifolds:
- In windy conditions, the stacked panels can be difficult to manage
- Bottom-track systems can trap debris
- Folded stack may obstruct furniture placement adjacent to the opening
Sliding Doors
Sliding doors move horizontally on tracks, with panels either sliding behind each other (standard sliding) or sliding into a wall pocket (pocket sliding). Contemporary slim-frame aluminium sliding systems have largely displaced older-style patio doors.
The practical reality of sliding doors:
- Panels slide in parallel, so at least half the opening is always covered by a panel
- Frameless or near-frameless systems with minimal sightlines are available
- No panels stack into the room — the frame footprint is entirely contained within the opening
- In-pocket sliding systems (where panels retract into wall pockets) allow a completely unobstructed aperture — more expensive but architecturally the cleanest solution
Strengths of sliding doors:
- Easier to operate in all weather — no large panels swinging
- No floor track required for top-hung sliding systems
- Cleaner appearance in some contemporary architectural contexts
- In-pocket systems achieve the most dramatic indoor-outdoor connection
Weaknesses of sliding doors:
- Standard sliding: you can only open up to 50% of the total width
- More expensive per m² than bifolds in most systems at equivalent quality
Materials
uPVC: Lower cost, lower thermal performance, less premium appearance. Not recommended for contemporary extension aesthetics in London — the sightlines are too thick and the appearance ages poorly.
Timber: Traditional, warm appearance. Higher maintenance requirement. Good thermal performance naturally. Most appropriate for period-restoration projects or very high-end contemporary work.
Aluminium: The dominant material for London rear extension doors. Slim sightlines, excellent thermal performance (with thermal break), powder-coat finish in any RAL colour, low maintenance. Available from many manufacturers at a range of price points.
Specification Points That Matter
Thermal break: All external aluminium glazed systems for habitable rooms should have a thermal break (a non-conductive material separating the inner and outer aluminium profiles). Without it, aluminium is extremely thermally conductive — cold bridges, condensation, and high heat loss.
Glass specification: Double-glazed units as a minimum for Building Regulations compliance. Triple glazing is available at higher cost and weight. Low-E coating on the glass significantly reduces heat loss. In south-facing rear extensions, solar control glass reduces summer overheating.
Security: Multi-point locking as standard. Shootbolt locking systems engaged at multiple points along the height of the door are significantly more secure than single-point locks.
Sill/threshold: A low or flush threshold is a significant accessibility and usability improvement. Some systems achieve near-flush thresholds without compromising weather-sealing performance.
Colour: Both inside and outside powder-coat colour should be specified. Many manufacturers offer dual colour (different inside and outside) at a premium.
Cost Guide (London, 2026 — Supply and Installation)
| System Width | Bifold (Aluminium) | Sliding (Aluminium) |
|---|---|---|
| 2.4m (2 panels) | £3,500–£5,500 | £3,000–£5,000 |
| 3.0m (3 panels) | £4,500–£7,000 | £3,800–£6,000 |
| 4.0m (4 panels) | £5,500–£9,000 | £4,500–£7,500 |
| 5.0m (5 panels) | £7,000–£12,000 | £5,500–£9,000 |
| 6.0m (6 panels) | £8,500–£14,000 | £6,500–£11,000 |
Premium manufacturers (Origin, Schüco, Reynaers) sit at the upper end of these ranges. Mid-range manufacturers (Smart Systems, AluK) deliver good quality at the middle of the range. Cheaper Far Eastern imports are available at lower cost but with shorter guarantees and less reliable after-sales support.
Lead times: Quality aluminium bifold and sliding systems have a lead time of 6–12 weeks from order. Order them no later than when foundations are poured. Receiving them on time is often on the critical path of a London extension programme.
RCB Design & Build
RCB supplies and installs bifold and sliding glazed systems on all London rear extensions. We advise on specification, manage the order timeline to programme, and install the system with correct weatherproofing and threshold detailing. Contact us to discuss your extension.