The short answer
Modern bifold doors need not be cold or draughty, but cheaper or poorly fitted ones can be, and a large glass area always feels cooler than a solid wall. Bifolds got a reputation for being chilly because early or budget systems had thin frames, basic glazing and several panels meeting along gaskets that could let air through. A well-specified bifold today — with a thermally broken aluminium or insulated frame, high-performance double or triple glazing, and good-quality weather seals — performs to modern energy standards and resists draughts. The things that decide it are the door's U-value (lower is warmer), the glazing, the quality of the gaskets where panels meet, and above all the standard of installation. Get those right and a bifold is comfortable; cut corners and it can feel cold.
The "bifolds are cold" worry is partly history and partly physics. The sections below explain where the reputation comes from, what actually determines warmth, and how to specify and fit a door that does not feel draughty.
What decides warmth
- FrameThermally broken/insulated = warmer
- GlazingDouble or triple, low-E
- SealsQuality gaskets at panel joints
- MeasureU-value (lower is better)
- Biggest factorInstallation quality
Where the cold reputation comes from
Two things drive the perception that bifolds are cold. The first is physics: any large expanse of glass loses heat faster and feels cooler to sit beside than an insulated solid wall, simply because glass conducts heat more readily. That is true of all glazed doors, not just bifolds, but a wide bifold replaces a lot of wall with glass, so the effect is noticeable.
The second is history. Early and budget bifold systems often had thin, non-insulated frames, basic glazing and several panels meeting along gaskets that were not always well sealed — so they did lose heat and could let draughts through at the joints. Those doors gave the type its chilly reputation. Modern, well-made systems are a different proposition, but the reputation lingers, which is why specification matters so much when buying.
What actually determines warmth
How warm a bifold feels comes down to a handful of measurable things. The headline figure is the U-value — how much heat passes through the whole door per square metre; the lower the number, the better the insulation. A quality modern bifold achieves a low whole-door U-value through three contributions: an insulated or 'thermally broken' frame (a non-conductive barrier inside aluminium frames that stops cold transferring through the metal), high-performance glazing (double or triple, with a low-emissivity coating and warm-edge spacers), and well-designed weather seals at every panel joint and the threshold.
| Element | Cold/draughty version | Warm version |
|---|---|---|
| Frame | Non-broken aluminium | Thermally broken / insulated |
| Glazing | Basic double | Low-E double or triple |
| Spacer bar | Standard aluminium | Warm-edge |
| Seals | Single, basic gaskets | Multiple quality gaskets |
| Threshold | Poorly sealed | Weather-sealed, low/flush |
| Whole-door U-value | Higher (worse) | Lower (better) |
Indicative comparison for guidance; ask for the quoted whole-door U-value.
How to avoid a cold, draughty bifold
Avoiding a chilly door is mostly about specification and fitting. On specification, choose a thermally broken aluminium or insulated frame, low-E double or triple glazing with warm-edge spacers, and ask the supplier for the quoted whole-door U-value so you can compare like for like. Solar-control glass is worth considering too — it limits summer overheating without making the door cold in winter.
On installation, even a top-quality door will still feel draughty if it is fitted into a poorly sealed opening or left out of adjustment so the gaskets do not compress evenly. A competent installer will fix the frame square and plumb, seal around it properly, and adjust the panels so they close tightly with the seals fully engaged. The threshold matters too: a well-detailed low or flush threshold should be weather-sealed and drained so it neither leaks water nor lets draughts in. Done properly, a modern bifold is comfortable year-round; the cold-and-draughty problem is almost always a sign of a budget system or a poor fit rather than anything inherent to bifolds.
Frequently asked questions
Do bifold doors let in draughts?
Cheap or poorly fitted bifolds can let draughts through at the panel joints or threshold, but a quality modern system with good gaskets, adjusted correctly and sealed into the opening, resists draughts well. Draughtiness is usually a sign of a budget door or a poor installation.
Are bifold doors warm enough for a UK winter?
Yes, if specified well. A thermally broken or insulated frame with low-E double or triple glazing achieves a low U-value and keeps a room comfortable through a UK winter. A large glass area always feels slightly cooler than a solid wall, but good glazing keeps this minor.
What U-value should a bifold door have?
Lower is better. Building Regulations set a maximum U-value for replacement doors, and quality bifolds comfortably beat it, with the strongest achieving low whole-door figures through insulated frames and high-performance glazing. Ask the supplier for the quoted whole-door U-value to compare options.
Sources & further reading
- gov.uk — Building Regulations Approved Document L (conservation of fuel and power)
- HomeOwners Alliance — bifold doors guide
Figures on this page are typical UK ranges drawn from published sources and depend on your specific opening and material. They are guidance, not a quotation.