Flagship guide · 9 min read
The Ultimate Guide to Sliding Doors
How aluminium sliding doors work, what separates a good system from a poor one, and what to expect from specification through to installed cost.
← Architectural Aluminium
Bifold Doors
Folding systems that open an elevation completely. Where a sliding door frames a view, a bifold removes the wall — the right choice for garden rooms, terraces and entertaining spaces.
5.0 from 7 Google reviewsWhen are bifolding doors the right choice over sliding doors?
Bifolding doors are the right choice when the point of the opening is to remove the wall entirely — for entertaining, for garden-facing kitchens, or where inside and outside are genuinely used as one space in summer. They open almost the full width, which sliding doors cannot. The trade-off is the stacked frames when open and more frame in the view when closed. If the doors are mostly shut and looked through, sliding doors usually read better; if they are thrown open, bifolds usually win.
Recent installations
Bifold Doors we have designed, surveyed and installed
See it in a real home
A House Rebuilt Around Its Glazing
A drone film over a whole-house remodel near Penrith — rising across the brick and render frontage, over the tiled hip and rooflight, then settling on the full-width glazed garden elevation.
See it in a real home
A Garden Room Glazed on Three Sides
A drone film over a brick garden room near Keswick — dropping from the rooftops onto the tiled gable and its rooflights, then working around two bifold runs folded open onto the terrace.
See it in a real home
A Whole House, Front to Garden
A drone film over a remodelled family house near Windermere — descending onto the render-and-brick front elevation and its bay windows, then rising over the ridge to the glazed garden room and lantern behind.
See it in a real home
Courtyard Garden Room, Brick Barn-Style New Build
A tracking film along a brick courtyard range in South Lakeland — paired aluminium French doors, full-height fixed screens between brick piers and a bifolding return onto sandstone paving.
Why this system exists
01
The whole opening, open
Panels stack neatly to one or both sides, leaving over 90% of the aperture clear.
02
Slim stacked sightlines
Narrow mullions keep the closed elevation disciplined rather than busy.
03
Traffic door included
A single access leaf for everyday use, so the full set is only opened when you want it.
04
Weather-sealed properly
Multi-point locking, brush and bubble gaskets and drained thresholds detailed for exposed sites.
Suitability
Where bifold doors belong, and where they do not
Best suited to
- Openings intended to be fully cleared, not partially opened
- Garden-facing kitchens and family rooms used as one space in summer
- Projects where a traffic door for everyday access is useful
- Openings where a stacking zone to one or both sides is available
Less suitable when
- Elevations where the closed view matters more than the open one
- Openings with no side wall or return to stack the panels against
- Very wide spans where a sliding arrangement gives calmer sightlines
- Highly exposed elevations where fewer opening joints are preferable
Bifold or sliding?
Bifolds win when you genuinely want the opening cleared — a terrace used daily in summer, a kitchen that becomes an outdoor room. Sliding doors win when the view matters more than the aperture, because the glass area is larger and the frame lines fewer.
We will recommend against a bifold where a slider serves the architecture better. That advice costs you nothing and saves regret.
Considered detailing is what separates a fitted window from a finished one.
Recent installs
Recently completed across Cumbria and the North West
Real installations from across Cumbria and the North West — surveyed, specified and installed under our own supervision.
Alunet Aluminium Picture Windows, Eco Forest Lodges
Ravenstonedale · 2026
Alunet Aluminium French Door Sets, Eco Forest Lodges
Ravenstonedale · 2026
Glazed Rear Elevation, Heritage Aluminium Windows
Near Penrith · 2025
24 Heritage Aluminium Windows, Matt Black
Near Penrith · 2025
Garden Room Glazed on Three Sides, Jet Black Bifolds
Near Keswick · 2025
Four-Panel Aluminium Bifold Run
Near Keswick · 2025
Aluminium French Door Sets In Original Brick Arches
Near Cartmel · 2025
Timber-Look uPVC Windows, Barn Conversion
Near Cartmel · 2025
Steel-Look Georgian-Bar Casements & Bay Windows
Near Windermere · 2025
Full-Width Garden Room Glazing & Lantern Rooflight
Near Windermere · 2025
Full-Width Slimline Sliding Doors, Clad Remodel
North West · 2025
Black Aluminium Picture Windows, Timber-Clad Elevation
North West · 2025
32 Heritage Windows and 4 Doors, Stone Self Build
West Yorkshire · 2025
Black Heritage Windows with Georgian Bars
West Yorkshire · 2025
Triangular Gable Glazing and Heritage Casements
West Yorkshire · 2025
Steel-Look Doors and Screens, Barn Conversion
North West · July 2026
Flush Casement Windows, Oak-Framed Garden Room
Cumbria · July 2026
Grey Aluminium Windows and Doors, Full Elevation
North West · July 2026
Steel-Look French Doors and Window Set
North West · June 2026
Anthracite Bifolding Doors, Brick Extension
North West · July 2026
Steel-Look Screen and Doors
North West · July 2026
Three-Panel Slimline Sliding Doors
North West · July 2026
Five-Panel Bifolding Doors, Cottage Extension
Cumbria · June 2026
Steel-Look Doors and Matching Screen
North West · June 2026
Slimline Sliding Doors, Brick Courtyard
North West · June 2026
Full-Width Steel-Look Glazed Screen
North West · June 2026
Heritage French Doors with Side Screens
North West · May 2026
Aluminium Windows and Glazed Doors
North West · May 2026
Bifolding Doors to a Barn Courtyard
Cumbria · May 2026
Gable-End Glazing and French Doors
North West · May 2026
Internal Steel-Look Screen
Cumbria · April 2026
Bifolding Doors, Clad Garden Room
Cumbria · April 2026
Aluminium Vertical Sliding Sash Windows
Cumbria · March 2026
Slim 20mm Sliding Door Set
Windermere · May 2026
Heritage French Door Set
Barrow · May 2026
Single Door and Window
Windermere · May 2026
AB60 Smart French Doors
Bowness · May 2026
Heritage Alunet Bifold Doors
Lancaster · May 2026
AS20 Smart Slimline Sliding Doors
Carlisle · January 2026
Farmhouse Extension Aluminium Windows
Carlisle · January 2026
Full House Aluminium Windows
Kirkby Stephen · August 2025
Technical
Specification at a glance
Figures shown are indicative system capabilities. Final performance depends on the chosen system, dimensions, glass make-up, configuration and installation detail, and is confirmed on the manufacturer data sheets issued with every quotation. Guarantee cover varies by product and component. The applicable frame, glazing, hardware and installation guarantees are set out in writing at quotation stage.
- Systems
- AB60 and heritage Alunet folding systems
- Configurations
- 2 to 7 panels, in-swing or out-swing, traffic door
- Max panel
- Up to 1.2m wide, 2.5m high
- Thresholds
- Flush or weathered
- Finish
- PPC RAL, dual colour
- Guarantees
- Confirmed by product and component with quotation
Choosing a system
AB-38 or AB-60 — how the two systems differ
Not all bifolds are the same door in a different colour. Frame strength, panel limits and thermal performance vary considerably between systems.
Alumil AB-38
Most slender · most glass
Currently the slimmest bifolding system in the UK, with an 88mm glass-to-glass sightline where panels meet. Specified where the visual impact of the opening is the point of the project.
- — High-end extensions
- — Contemporary new builds
- — Minimal aluminium, maximum glass
Smart AB-60
Proven · serviceable
A refined version of one of Britain's most installed folding systems. Its adjustment mechanism allows the doors to be fine-tuned years later without removing the glass — a genuine advantage over a twenty-year life.
- — Family homes
- — Extensions and renovations
- — Premium quality without extreme slimline
| Alumil AB-38 | Smart AB-60 | |
|---|---|---|
| Position | Slimmest available | Balanced premium |
| Sightline where panels meet | 88mm | 120mm |
| Max panel width | 1300mm | 1200mm |
| Max panel height | 3000mm | 2500mm |
| Max sash weight | 140kg | 100kg |
| Glazing | Double (triple not required) | Double or triple |
| Double glazed U-value from | 1.1 W/m²K | 1.5 W/m²K |
| Triple glazed U-value from | Not required | 1.2 W/m²K |
| Thresholds | Flush or low | Flush or weathered |
Published U-values are based on standard test sizes. Installed performance varies with panel size, glass make-up, threshold and configuration.
Specify it your way
Colours, glass, hardware and details worth saving
Save anything that appeals and it travels with you — into your Inspiration Collection and then into your consultation.
Frame colours
- RAL 7016 AnthraciteThe contemporary default — quiet against stone and render alike.
- Pure White InteriorDual-colour frames that disappear from inside the room.
- Jet BlackSteel-look elevations and rural conversions.
- Painted CreamTraditional joinery language for cottages and farmhouses.
Glass & glazing
- Corner pocket glazingTwo elevations opening into one another with no corner post.
- Slim 20mm sliding sightlinesMaximum glass, minimum frame, panes that stack behind one another.
- Full-height fixed panesFrameless-feeling picture glazing framing one specific view.
Hardware
- Flush lever handlesMinimal, colour-matched and unobtrusive on modern frames.
- Concealed hingesNothing interrupting the sightline when the frame is closed.
- Monkey-tail handlesForged period detailing for heritage and conservation openings.
Design features
The whole opening, open
Panels stack neatly to one or both sides, leaving over 90% of the aperture clear.
Slim stacked sightlines
Narrow mullions keep the closed elevation disciplined rather than busy.
Traffic door included
A single access leaf for everyday use, so the full set is only opened when you want it.
Weather-sealed properly
Multi-point locking, brush and bubble gaskets and drained thresholds detailed for exposed sites.
How it is fitted — filmed on site
Fitting a Gable-End Apex Screen
Two installers set, pack and level a raked aluminium gable screen on a first-floor deck, then glaze the apex — filmed over a working morning.
0:32 · Windermere, Cumbria · August 2025
This is the part of a project homeowners rarely get to watch: a raked, gable-end aluminium screen being set into a finished opening at first-floor level. The frame is offered up dry, packed off the structure, checked for plumb and level, and only then fixed and glazed.
Everything about the sequence is deliberate. The deck is boarded and the working area kept to one side so the finished surfaces below are never used as a workbench. Packers carry the load at fixed points rather than the frame being pulled square with fixings. The apex angle is cut and jointed in the factory to the surveyed pitch, so nothing is adapted on site.
- System
- Smart aluminium, gable-end apex screen
- Stage shown
- Frame fitting through to sealing and finishing
- Access
- First-floor deck, boarded working zone
- Frames
- Powder-coated aluminium, raked to the roof pitch
- Glazing
- Double glazed units, externally glazed, internally beaded
- Filmed
- Windermere, Cumbria, August 2025
Frame fitting, packing and levellingGlazing the unitsAdjustment and alignmentWeather sealingTrims and finishing
How it is fitted — filmed on site
Commissioning a Four-Panel Sliding Door Run
The moment a glazed, fifteen-metre sliding run is first moved on its track — the commissioning and adjustment stage, filmed on a garden room build near Grasmere.
0:17 · Near Grasmere, Cumbria · September 2025
This is the stage homeowners feel every single day for the next twenty years, and the one that separates a competent fit from a genuinely good one. The frames are in, the units are glazed, and the installer is now running each panel end to end by hand — repeatedly — to prove the track, the rollers and the interlocks before anything is signed off.
What you are watching is a test, not a demonstration. A correctly commissioned sliding panel moves with one hand, at the same effort from one end of the run to the other, and stops dead where you let go of it. Any change in resistance across the track means the cill is not perfectly level or the rollers need setting, and that is corrected now — while the building is still open and everything is accessible.
- System
- Slimline aluminium sliding doors, multi-panel run
- Stage shown
- Glazing through to commissioning, adjustment and handover
- Setting
- Single-storey garden room, timber frame, open to the field
- Threshold
- Low-level track set into the deck structure
- Frames
- Powder-coated anthracite grey aluminium
- Filmed
- Near Grasmere, Cumbria, September 2025
Glazing the unitsAdjustment and alignmentTrims and finishingClean down and handover
Brochure
The Bifold Doors guide, including the mistakes worth avoiding
Configurations, sightline comparisons, structural considerations and the questions to ask before you order. Printed copies posted on request.
Start the conversation
If you are planning an extension, renovation or new-build project and want glazing designed and installed without compromise, we would be glad to talk.
Direct
01768 254554projects@windowsinthelakes.co.ukBased in Appleby-in-Westmorland, with installation teams across Penrith, Keswick, Kendal, Windermere and the South Lakes.
Common questions
Bifold Doors: your questions answered
Practical answers to what homeowners ask us most about this system. Anything else, just ask.
Book a Design ConsultationVisit the Knowledge CentreKnowledge Centre
Guides worth reading first
Flagship guide · 8 min read
The Complete Guide to Indoor–Outdoor Living
Indoor-outdoor living is a genuine design discipline, not just a wide door. Done well, it works through a grey Cumbrian February as well as a warm August evening.
Buying Guides · 3 min read
Bifold Door Buying Guide
A practical guide to choosing bifold doors: configurations, tracks and thresholds, glass, and how they compare with sliding doors for cost and everyday use.
Get an initial project price
Considering bifolding doors for your extension or garden room?
Send us the opening size, drawings or photographs and we’ll advise on the panel configuration, likely system and budget.
Not sure if this would suit your home?
Share a photograph and we’ll show you how this collection works on properties like yours.
Wondering what this collection typically costs?
Plan your project investment with a guide based on comparable completed projects.
Designed with
Frequently paired with this collection.
RAL 7016 Anthracite GreyColours Studio
Solar Control GlassGlass Studio
Brushed Bronze Pull BarHardware Studio
Flush ThresholdsDesign Details
Obscure Glass CollectionGlass StudioDual Colour: Anthracite / WhiteColours Studio
Design Studio
Keep exploring in the Design Studio
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Let’s design something exceptional.
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