A simple guide to bi-fold doors. Learn sightlines, thermal breaks, security, and how to choose the right system with clarity. Expert advice from GFD Homes.
What You’ll Learn:
- How Bi-Fold Doors Work and Why They’re So Popular
- How the Top Three Brands Compare
- What to Consider Before You Buy
- How to Ensure a Smooth, Stress-Free Purchase
(Estimated Reading Time: 5-6 Minutes)
Introduction: Folding Glass, Folding Heads
Bi-fold Doors look effortless on TV — huge walls of glass sliding away to open your home into the garden. But once you start researching, it quickly turns into a world of sightlines, thermal breaks, U-values, and traffic doors.
This guide breaks everything down in everyday English. Whether you’re exploring Korniche, Smart, or Cortizo systems, you’ll learn exactly what matters, what’s marketing noise, and how to choose bi-fold doors with total confidence.
What a Bi-Fold Door Actually Is
A Bi-fold Door is a set of glazed panels (called “leaves”) that fold and slide along a track, opening up entire walls.
They’re made from slim aluminium frames with large glass sections to let in maximum light.
When closed, they look like an elegant glazed wall. When open, they stack neatly to one side — giving you a completely open space between home and garden.
Available in 2 to 7 panels, bi-folds can open inwards or outwards, from the left, right, or middle.
Bi-Fold Doors Key Terms Explained
1. Sightlines
The sightline is the visible width of the vertical frame between glass panes.
Slimmer sightlines = more glass, less frame, more light.
Typical range: 110–132 mm depending on brand.
Why it matters: The thinner the sightline, the sleeker and more contemporary your view.
Consider: Ultra-slim systems like Cortizo if you prioritise minimal frame aesthetics.
2. Thermal Break
A thermal break is an insulating barrier (often a polyamide strip) inside the aluminium profile.
It stops heat escaping through the metal.
Why it matters:
Without a thermal break, aluminium conducts heat — meaning higher bills and condensation.
Modern systems like Smart Visofold and Korniche use multi-chambered thermal breaks to achieve U-values as low as 1.4 W/m²K.
3. Traffic Door
One leaf in a bi-fold can act as a normal hinged door.
That’s called a traffic door — handy for everyday use when you don’t want to fold the whole set open.
Why it matters:
Ideal for access to your garden or patio in winter, without losing heat.
Consider: If you use your patio often, make sure your design includes a traffic door.
4. Threshold
The threshold is the bottom track the doors slide on.
There are two main types:
- Low threshold: Flush with the floor for step-free access (great for wheelchairs and children).
- Rebated threshold: Sits slightly higher, offering better weatherproofing.
Tip: If your bifold doors are fully exposed to wind or rain, choose rebated. If sheltered or internal, low is fine.
5. Polyamide Strip
This is the technical name for the thermal barrier inside the aluminium frame.
It prevents heat transfer and is essential for energy efficiency.
Why it matters:
If a brochure mentions “polyamide thermal breaks,” that’s a good thing — it’s doing the insulation work you can’t see.
6. Glazing Bead / Internally Glazed
A glazing bead holds the glass in place.
When a door is internally glazed, the bead is on the inside — which means the glass can’t be removed from outside.
Why it matters:
It’s a security feature. Always look for internally glazed systems, like those sold by GFD Homes.
7. U-Value
Measures how well the door insulates.
Lower = better.
Typical range: 1.4–1.6 W/m²K depending on glass type.
Why it matters:
A low U-value keeps rooms warmer and cuts heating bills. For comparison, old patio doors often had U-values above 3.0.
8. PAS 24 / Secured by Design
PAS 24 is a British Standard for security testing — a door must resist physical attacks to pass.
Secured by Design (SBD) is a police initiative that sets even stricter standards.
Why it matters:
If security’s a concern, check for PAS 24 or SBD certification on your system.
9. Panel Configuration
This refers to how the panels fold and where they open from (e.g. 3L, 3R, 3L1R).
Why it matters:
The configuration determines:
- Where the panels stack.
- Whether you can include a traffic door.
- How space inside/outside is affected.
Consider: For smaller openings, go even-numbered panels (2 or 4). For larger spans, odd-numbered gives you a traffic door.
The Big Three: Korniche, Smart & Cortizo
Korniche Bi-Fold Doors
- From £1,250 inc VAT
- Fastest-fit UK system.
- Ultra-smooth glide track and slim 110 mm sightlines.
- 17 colours plus dual-colour options.
- PAS 24 security.
Smart Visofold 1000 / 6000 Bi-Fold Doors
- From £1,502 inc VAT
- Reliable, robust, widely specified in UK homes.
- Over 200 RAL colour options.
- Thermal break with U-values down to 1.4 W/m²K.
- Excellent all-round balance of performance and price.
Cortizo Slimline Bi-Fold Doors
- From £1,500 inc VAT
- Premium European engineering.
- Ultra-thin sightlines, perfect for architectural homes.
- High strength-to-weight ratio and luxury feel.
Common Confusions Explained
| Term | What People Think | What It Actually Means |
|---|---|---|
| Threshold | A design detail | The barrier keeping water/draughts out |
| Sightline | A visual term | The width of visible frame between panes |
| Traffic Door | Optional extra | Essential if you want daily access |
| Thermal Break | Marketing fluff | Crucial layer that keeps heat inside |
| PAS 24 | Random code | Proof of security testing |
| Internally Glazed | Decorative | Security feature preventing glass removal |
What to Think About Before Ordering
- Opening Direction: Do you want the panels stacking left, right, or split?
- Traffic Door: Do you need everyday access?
- Exposure: Choose thresholds and seals suitable for your weather conditions.
- Colour & Finish: Match to windows and other aluminium products.
- Space Planning: Ensure furniture, lighting, and paths don’t clash with stacking panels.
Buying Smart: Get It Right the First Time
At GFD Homes, every bi-fold door is made to measure and priced online to the millimetre.
That means no vague estimates — just clear, instant pricing before you commit.
You can even pair your bifolds with:
- Roof Lanterns for open-plan light.
- Matching Aluminium Windows for a seamless finish.
All backed by genuine warranties and UK-wide delivery.
Warranty Tip: Buy in Your Name
If you place the order, your warranty and consumer rights sit with you.
If your builder orders it, the warranty belongs to them — which can make aftercare complicated.
At GFD Homes, we recommend ordering directly under your name to stay protected and deal directly with our aftercare team.
Summary: Knowledge is Power
You now understand:
- What sightlines, thresholds, and thermal breaks actually do.
- Why a traffic door matters more than you thought.
- How U-values and PAS ratings protect your comfort and security.
- And how to buy smarter, safer, and with confidence.
With GFD Homes, you get transparency, expertise, and products we’d proudly install in our own homes.
🛒 Browse the full collection at www.gfdhomes.co.uk
📞 Or call 01642 309576 for expert guidance and a no-pressure quote.
In a rush? Why not contact us via Whatsapp
Bi-Fold Doors: Browse Our Articles
- Cortizo Bi-Fold Plus: An Introduction
- Why bi-fold doors are still popular…
- Are Bifold Doors Secure? Your Bifold Door Security Guide
- Trade access to bifold door costs: looking for trade prices? Visit our trade site, The Trade Village
FAQ’s
1. Are bi-fold doors better than sliding doors?
It depends on how you use the space. Bi-fold doors create a fully open wall, while sliding doors offer uninterrupted glass when closed. Bi-Fold Doors : Bi-Fold Doors Demystified: What All Those Specs Actually Mean explains how panel setup affects openness, sightlines, and layout.
2. Do bi-fold doors lose heat easily because they’re made of glass?
No — modern bi-fold doors use thermal breaks, polyamide strips, and high-performance glazing to keep U-values low. As covered in Bi-Fold Doors : Bi-Fold Doors Demystified: What All Those Specs Actually Mean, top systems can reach U-values around 1.4–1.6 W/m²K.
3. Do I need a traffic door?
If you want everyday access without opening the full set, yes. A traffic door acts like a normal hinged door for quick trips outside. This is explained in Bi-Fold Doors : Bi-Fold Doors Demystified: What All Those Specs Actually Mean.
4. What’s the difference between low and rebated thresholds?
Low thresholds offer seamless access; rebated thresholds provide better weatherproofing. Bi-Fold Doors : Bi-Fold Doors Demystified: What All Those Specs Actually Mean outlines which is best based on exposure to rain or wind.
5. How secure are bi-fold doors?
With features like PAS 24 testing, multi-point locks, and internal glazing, modern bi-fold doors are highly secure. Security standards are covered in Bi-Fold Doors : Bi-Fold Doors Demystified: What All Those Specs Actually Mean.
