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The Expert’s Guide to Bifold Doors: Thresholds, Traffic Doors & Technical Specs
The Expert’s Guide to Bifold Doors: Thresholds, Traffic Doors & Technical Specs
Most bifold door guides stop at “they look nice.” But if you are planning to spend thousands of pounds on a home improvement, you need the technical details. You need to understand how the water drainage works, how the doors stack, and how to stay legal with Building Regulations.
At KJM Group, we want you to be an informed buyer. This technical guide covers the critical decisions you need to make: Thresholds, Configuration, and Regulations.
- 🛑 Weathered Thresholds are essential for external use to prevent leaks and drafts in the UK climate.
- 🚪 Traffic Doors are a must-have. A “3+1” or “3-panel” setup gives you a daily door without opening the whole wall.
- 📋 Part L & F: New doors must meet strict U-values (1.4 W/m²K) and usually require trickle vents for background ventilation.
- ☀️ Solar Control: South-facing bifolds can overheat a room. Integral blinds or solar glass are highly recommended.
1. The Threshold Dilemma: Flush vs. Weathered
The most common request we get is: “I want a completely flush floor from my kitchen to my patio, with no step.”
While this looks amazing in magazines, there is a harsh reality to face: True flush thresholds are not weather-proof.
Because a flush threshold has no “upstand” or rebate, there is nothing for the door seals to compress against. This means they offer little resistance to wind-driven rain and air pressure.
2. Configuration Logic: The “Traffic Door” Secret
If you have a wide aperture, the configuration (how the doors split) is critical. You need to decide if you want a Traffic Door—a single panel that opens independently like a normal back door, so you don’t have to unlock the entire sliding mechanism just to let the dog out.
📐 Panel Configurator
Enter your opening width to see our recommendation:
3. Solving the “Goldfish Bowl” Problem (Integral Blinds)
Bifold doors are essentially a wall of glass. In summer, this can lead to solar gain (overheating), and in winter evenings, it can feel like a “black hole” with zero privacy.
Traditional curtains often get in the way of the folding mechanism. This is why we strongly recommend Integral Blinds. These are Venetian-style blinds sealed inside the double-glazed unit. They never need dusting, they don’t dangle, and they move with the door panels perfectly.
👉 Learn more about KJM Integral Blinds here.
4. Building Regulations (The Boring but Important Stuff)
Since the update to Building Regulations in 2022, compliance has become stricter.
- Part L (Conservation of Fuel & Power): Any new door installed in an existing dwelling must achieve a U-Value of 1.4 W/m²K or better. Our Aluminium systems (Smart Visofold and Korniche) meet these strict targets.
- Part F (Ventilation): If you are replacing windows or doors that had trickle vents, the new ones must also have them. Even if the old ones didn’t, we are usually required to install trickle vents to ensure “background ventilation” for healthy air quality.
Detailed FAQ: Technical Specs
We generally prefer Bottom Rolling systems for bifolds. Top-hung doors put all the weight (which is significant with triple glazing) on the lintel above, requiring massive structural support. Bottom rolling transfers the weight directly to the floor, which is mechanically more stable and smoother to operate over time.
Yes. A popular choice is Anthracite Grey (RAL 7016) on the outside to look modern, with White (RAL 9910) on the inside to keep your interior bright and match your skirting boards. This is standard for our aluminium ranges.
Both are premium aluminium systems. Visofold 1000 is the industry standard—reliable, robust, and slightly more traditional in profile. Korniche is often praised for its “cleaner” aesthetics and slightly slimmer engineering. We have both available to view in our Andover showroom.
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Mark Pearce is a highly experienced specialist in the double glazing industry, having built his knowledge from the ground up through hands-on experience in installation, manufacturing, sales, and business management. Beyond his role at KJM, Mark is a keen blogger, writer, and traveller, often sharing insights on the latest innovations in the home improvement industry.
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