Bifold vs Sliding Doors for Extensions: Complete London Guide 2026
The doors you choose for your extension will define how the space feels, how it connects to your garden, and how much natural light floods in. Here is everything you need to know about bifold and sliding doors for London extensions.
Quick Answer
Bifold doors cost £3,000-8,000 and open up to 90%+ of the aperture, ideal for indoor-outdoor flow. Sliding doors cost £4,000-12,000 with slimmer sightlines and better thermal performance, but only open 50% of the width.
£3k-£8k
Bifold Cost
£4k-£12k
Sliding Cost
90% vs 50%
Opening Width
Check your specific property constraints
Free Property CheckWhy Your Door Choice Matters More Than You Think
The glazing on your extension is not just a practical element. It is the single biggest design decision that shapes the character of the entire space. The right doors transform a standard kitchen extension into a light-filled room that feels twice its size.
In London, where rear gardens are often compact and extensions push right up to boundary lines, the connection between indoors and outdoors is especially valuable. Your door choice affects three critical factors:
- Natural light: Larger glass areas and slimmer frames mean more daylight penetration, reducing reliance on artificial lighting during the day
- Indoor-outdoor flow: How seamlessly your kitchen or living space connects to the garden, especially during summer entertaining
- Property value: Estate agents consistently report that high-quality glazing is one of the first features buyers notice in an extended home
Bifold Doors Explained
Bifold doors consist of multiple panels (typically 3 to 7) that fold in a concertina action and stack neatly to one or both sides of the opening. When fully open, they create an almost entirely clear aperture, effectively removing the barrier between your extension and garden.
They run on a top and bottom track system, with each panel hinged to the next. Most configurations include a traffic door that opens independently for everyday access without folding all the panels.
Advantages of Bifold Doors
- 90%+ clear opening: When fully folded back, almost the entire width of the aperture is open, creating a dramatic connection to the garden
- Flexible opening widths: You can open 2, 3, or all panels depending on weather and needs, giving you precise control over airflow
- Excellent ventilation: The wide opening allows significantly more air circulation than sliding doors, a real benefit in summer
- Entertainment-friendly: Perfect for summer barbecues and parties where you want the garden and kitchen to feel like one space
- Traffic door: Most systems include a single door that opens independently for everyday in-and-out access
Disadvantages of Bifold Doors
- Panels stack to one side: When open, the folded panels take up space at one or both ends of the opening, reducing the usable width by 10-15%
- Threshold trip hazard: The bottom track is typically 20-30mm above floor level, creating a step that can be problematic for wheelchair users and young children
- More maintenance required: Multiple hinges, rollers, and tracks need regular cleaning and lubrication to operate smoothly
- Wind exposure: Open panels can catch the wind and slam shut, which is a consideration for exposed London rooftop terraces or windy garden locations
- Wider frame profiles: Each panel needs a frame, so with 4-5 panels you have 4-5 vertical frame sections reducing your glass area compared to sliding
Typical bifold cost: £3,000 to £8,000 for a 3-4 metre opening in aluminium. Budget brands start around £2,500, while premium systems from Origin, Schuco, or Reynaers can reach £10,000 or more for wider openings.
Sliding Doors Explained
Sliding doors consist of two or three large glass panels that glide horizontally along a track. One or two panels slide behind the fixed panel, creating an opening on one or both sides. The panels are significantly larger than bifold panels, often 1.5 to 3 metres wide each.
Modern sliding door systems have evolved dramatically. Contemporary aluminium frames can be as slim as 20mm, creating an almost frameless wall of glass that maximises your view of the garden. Lift-and-slide mechanisms make even 3-metre-wide panels effortless to operate.
Advantages of Sliding Doors
- Clean, minimal aesthetic: Fewer frame sections mean more uninterrupted glass, giving your extension a contemporary, high-end look
- Ultra-slim sightlines: Premium systems offer 20-35mm frame widths compared to 50-70mm on bifolds, maximising the glass-to-frame ratio
- Flush threshold option: Many systems offer a fully recessed track that sits flush with the floor, eliminating trip hazards and improving accessibility
- Better thermal performance: Fewer joints and gaskets mean less air leakage, typically achieving lower U-values than equivalent bifold systems
- Less maintenance: Only 1-2 moving panels with simple roller mechanisms, compared to multiple hinges on bifolds
Disadvantages of Sliding Doors
- Maximum 50% opening: One panel always remains fixed, so you can never open more than half the total width (or two-thirds with a 3-panel system)
- Less ventilation: The smaller opening means reduced airflow compared to a fully open bifold wall
- Heavier to operate: Large glass panels can weigh 80-150kg each, requiring quality hardware and proper track maintenance
- Higher entry price: The engineering required for large sliding panels and slim frames pushes the starting cost above bifolds
Typical sliding door cost: £4,000 to £12,000 for a 3-4 metre opening in aluminium. Premium slim-frame systems from IQ Glass, Vitrocsa, or Keller start around £8,000 and can exceed £20,000 for bespoke configurations.
Head-to-Head Comparison
This table compares the key factors side by side to help you decide which system suits your extension project.
| Factor | Bifold Doors | Sliding Doors |
|---|---|---|
| Aesthetics | Contemporary, slightly busy frame lines | Minimal, clean wall of glass |
| Opening % | 90-95% of aperture | 50-66% of aperture |
| Thermal Performance | U-value 1.4-1.6 W/m2K typical | U-value 1.2-1.5 W/m2K typical |
| Maintenance | Higher - multiple hinges and rollers | Lower - fewer moving parts |
| Cost (3-4m) | £3,000-£8,000 | £4,000-£12,000 |
| Wind Resistance | Panels can catch wind when open | Panels track-guided, wind stable |
| Threshold | Typically raised 20-30mm | Flush threshold available |
| Planning | Usually no issue under PD | Usually no issue under PD |
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Which Works Better for London Extensions?
London properties have specific characteristics that influence which door type works best. Garden size, extension width, and how you use your outdoor space all play a role.
Small Gardens: Sliding Doors Often Win
If your garden is under 8 metres deep (common in inner London terraces), sliding doors often make more sense. The clean, uninterrupted glass creates a visual connection to the garden that makes both spaces feel larger. You are looking at the garden more than stepping into it, so the 50% opening limitation matters less.
Slim-frame sliding doors also work beautifully with small courtyard gardens, where the goal is to frame the planting and create a sense of calm rather than throw the entire wall open.
Entertaining and Family Life: Bifold Doors Shine
If you host barbecues, children run between kitchen and garden, or you simply want the option to completely merge indoors and outdoors on warm days, bifold doors deliver. The 90% opening width means you can position a dining table right at the threshold and serve straight from the kitchen to guests seated outside.
For families with young children, bifolds also make it easier to supervise kids in the garden while cooking, as there is no fixed panel blocking your sightline.
London trend: Over the past five years, sliding doors have overtaken bifolds in popularity for high-end London extensions. Architects favour them for the cleaner aesthetic, but bifolds remain the more popular choice for family-focused kitchen extensions where the full opening width is valued.
Planning your extension doors?
Get instant advice on the best option for your propertyPlanning Permission Considerations
The good news is that your choice between bifold and sliding doors rarely affects planning permission. Both are standard glazing options for extensions and are accepted under Permitted Development without issue.
However, there are a few scenarios where your door choice could become a planning consideration:
- Conservation areas: Some councils restrict frame colours. Black or dark grey aluminium is almost always accepted, but unusual colours may need approval. Timber frames may be preferred in highly sensitive areas
- Overlooking concerns: If your extension faces a neighbour's property closely, planners may request obscured glass in certain panels regardless of door type
- Listed buildings: Listed building consent will cover all external materials including door systems. Expect the conservation officer to have strong opinions on frame profiles and materials
Building Regulations: Part L Thermal Performance
Under Part L of the Building Regulations (updated June 2022), all new doors and windows in extensions must meet minimum thermal performance standards. The maximum permitted U-value for doors is 1.4 W/m2K for new extensions.
Both bifold and sliding door systems from reputable manufacturers comfortably meet this requirement. However, sliding doors tend to achieve slightly better U-values because they have fewer joints and gaskets where heat can escape.
| Specification | Bifold Doors | Sliding Doors |
|---|---|---|
| Part L Maximum U-value | 1.4 W/m2K | 1.4 W/m2K |
| Typical Achieved U-value | 1.3-1.6 W/m2K | 1.0-1.5 W/m2K |
| Glazing | Double or triple glazed | Double or triple glazed |
| Air Leakage | Higher risk (more seals) | Lower risk (fewer seals) |
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Cost Comparison by Opening Width
The cost gap between bifold and sliding doors varies depending on the opening width. Smaller openings show less difference, while wider openings can see significant price variation. All prices below are for mid-range aluminium systems, supply and installation.
| Opening Width | Bifold (Aluminium) | Sliding (Aluminium) | Difference |
|---|---|---|---|
| 2m (2 panels) | £2,000-£3,500 | £2,500-£4,500 | +£500-£1,000 |
| 3m (3 panels) | £3,000-£5,500 | £4,000-£7,500 | +£1,000-£2,000 |
| 4m (4-5 panels) | £4,500-£8,000 | £6,000-£12,000 | +£1,500-£4,000 |
| 5m (5-6 panels) | £5,500-£10,000 | £8,000-£16,000 | +£2,500-£6,000 |
Installation note: These prices include professional installation. DIY installation is not recommended for either system as incorrect fitting voids warranties, compromises thermal performance, and can cause operational problems. Budget an additional £800-1,500 for structural steelwork above the opening if your builder has not already included this.
Frequently Asked Questions
Are bifold or sliding doors more secure?
Both achieve equivalent security ratings when specified correctly. Look for PAS 24:2016 certification on either system, which is the UK standard for enhanced security doors. Most quality aluminium bifold and sliding doors from major manufacturers come with PAS 24 as standard. Sliding doors can have a slight edge as the fixed panel cannot be removed from outside, while bifold panels could theoretically be lifted from their tracks if security hardware fails.
Can I mix bifold and sliding doors on the same extension?
Yes, and this is becoming increasingly popular for corner extensions or L-shaped openings. A common London approach is sliding doors on the main rear wall (for the clean aesthetic) and a smaller bifold set on a side wall for access to a patio. Ensure both systems come from the same manufacturer or at least use matching frame profiles and colours for visual consistency.
Do bifold doors let in draughts?
Modern aluminium bifold doors from quality manufacturers are well-sealed and achieve excellent airtightness ratings. However, because they have more joints and gaskets than sliding doors (one per panel), there is theoretically more opportunity for seals to degrade over time. Annual cleaning and lubrication of seals prevents this. Budget bifold systems under £2,500 can be noticeably draughtier than mid-range and premium options.
What frame colour is most popular for London extensions?
Anthracite grey (RAL 7016) remains the most popular choice, accounting for around 50% of London installations. Matt black (RAL 9005) is growing in popularity, especially for contemporary extensions. White aluminium is less common but works well on period properties where the extension design is more traditional. Most manufacturers offer dual-colour options with a different colour inside and out, at a 15-20% price premium.
How long do bifold and sliding doors take to install?
Bifold doors for a typical 3-4m opening take 1-2 days to install once the structural opening is prepared. Sliding doors take 1-2 days as well, though large panels may need a crane or additional labour for lifting into position. The structural opening (steel beam, lintels) should be prepared by your builder before the door company arrives. Total lead time from order to delivery is typically 6-10 weeks for either system.
Are triple-glazed bifold or sliding doors worth the extra cost?
Triple glazing adds 20-30% to the door cost but improves the U-value by approximately 30%. For most London extensions, double-glazed doors with a U-value of 1.2-1.4 W/m2K are sufficient to meet Building Regulations. Triple glazing becomes worthwhile if your extension faces north, has a very large glazed area (over 60% of the rear wall), or you are targeting a high-performance build standard like Passivhaus.
Summary: Bifold vs Sliding Doors
Choose bifold doors if you prioritise maximum opening width (90%+), flexible ventilation, and indoor-outdoor entertaining. Best for family homes with gardens over 8m deep where children and adults move freely between kitchen and garden. Budget from £3,000 for a 3-4m opening.
Choose sliding doors if you value a clean minimal aesthetic, slim sightlines, better thermal performance, and lower maintenance. Ideal for smaller London gardens where framing the view matters more than opening the entire wall. Budget from £4,000 for a 3-4m opening.
Planning and building regs: Neither system causes planning issues under Permitted Development. Both meet Part L thermal requirements when properly specified. Conservation areas may restrict frame colours but accept both door types.
The real deciding factor is how you use your space. If you picture summer evenings with the entire wall folded back, choose bifolds. If you picture a beautiful, uninterrupted wall of glass that frames your garden year-round, choose sliding.
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