A rear extension and a set of bifold doors go hand in hand: the doors are what turn a new room into a bright, open space that connects to the garden. But a few decisions made early will determine how well they perform and look for years. Here is what to think about when choosing bifold doors for an extension.
Bifold door size and panel count
Most rear extensions suit a three-panel or four-panel bifold, opening up roughly 2.4m to 3.2m of wall. Decide early whether you want a traffic door — a single panel you can use day to day without folding the whole set back — as this affects the configuration and should be designed in from the start. Our guide to bifold door panel configurations explains the options.
Glazing and thermal performance
For an extension you will spend a lot of time in, specify good glazing: double glazing as standard, with options for solar-control glass to reduce overheating in south-facing rooms, or acoustic glass if you are near a road. A thermally broken aluminium frame keeps the room comfortable year round and can meet current Part L requirements — our building regulations guide explains what applies.
Thresholds, colour and system
- Threshold — a low or flush weathered threshold gives a near-level transition to the patio and is more accessible, while a standard threshold offers the highest weather resistance; some systems, such as the Schüco AS FD 75/90.HI, offer several threshold heights
- Colour — anthracite grey (RAL 7016) is the most popular modern finish, but aluminium can be powder-coated in almost any RAL colour, including dual-colour inside and out
- System — premium systems such as Schüco and Cortizo offer slimmer sightlines, strong security and long guarantees; our Schüco vs Cortizo guide helps you choose
The best bifold door systems for an extension, compared
There is no single best bifold door: the right one depends on the width of the opening, the threshold you want and how well insulated the extension is. These are the aluminium systems we make, with the figures that usually decide it. All of them are tested to PAS 24.
| System | Best suited to | Key figures |
|---|---|---|
| Schüco AS FD 75/90.HI | A near-level step onto the patio, and large panels | Panels up to 1500mm wide and 3500mm high; thresholds of 71mm, 15mm or 4mm; U-value 1.0 W/m²K; RC 2 |
| Cortizo Bifold | Wide openings with many panels | Panels up to 1200mm by 3000mm; up to 14 sashes; 120mm sightline where panels meet |
| Cortizo Bifold Plus | Large, well-insulated extensions and new builds | 110mm central section; 45mm thermal break; U-values from 0.8 W/m²K |
| Schüco ASS 70 FD | Openings where the leaves slide to either side | Folds inward or outward; vents up to 3 m²; U-values as low as 1.3 W/m²K |
| Schüco cornerless | Corner extensions and garden rooms | No post at the corner, so the structure above must span the opening |
Whichever system you choose, the doors sit in an outside wall, so the threshold, opening direction and drainage matter as much as the frame; our external bifold doors page explains each choice. If your builder is fitting the doors, they can be ordered supply only for the trade.
Bifold or sliding doors for an extension?
If you spend more time looking at the garden than walking into it, sliding doors may suit the extension better, with larger panes and slimmer frames — our bifold vs sliding doors guide compares the two. For rooms set back from the garden, a roof lantern adds daylight from above. On the Wilderness Reserve estate in Suffolk, for example, we supplied and installed slimline folding sliding doors and aluminium windows across a collection of country houses.
Planning the doors with your builder
Coordinate the doors with your builder early. The structural opening, lintel and floor level all need to suit the doors you choose, so it pays to confirm the specification before the brickwork goes up. For budgeting, see our bifold door cost guide: most 3–4 panel aluminium bifolds fall between £3,000 and £6,000 supplied and fitted including VAT.
Frequently asked questions
What size bifold door do I need for an extension?
Most rear extensions suit a three- or four-panel bifold door, covering an opening of roughly 2.4m to 3.2m. Wider openings use five panels or more.
Do I need a steel or lintel for bifold doors?
If you are forming or widening an opening, yes. A correctly sized lintel or steel beam needs to be designed by a structural engineer and approved by building control. Final door measurements are best taken once the opening is formed.
Planning an extension? Tell us your opening size and we will help you specify the ideal bifold doors and send a free quote — supply only or supply and fit.
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