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Bifold Doors Building Regulations: When You Need Approval, the U-Value to Hit, and the Glazing Limit in an Extension
Bifold doors building regulations depend on one question: are you replacing doors in the same opening, or making the opening bigger? A like-for-like swap fitted by a registered installer needs no application to building control; the installer self-certifies that the new doorset meets the energy and safety rules. Widen the opening, knock through a wall or put bifolds in an extension, and building control is involved, because the structure changes. This page sets out both routes, the numbers your doors must meet, and where planning permission comes in.
Bifolds are a controlled fitting
The Building Regulations 2010 treat a new or replacement door as a “controlled fitting” when more than half of its internal face is glazed. Bifolds almost always are. That means the whole unit, frame included, has to meet the energy efficiency standards in Approved Document L. Replacing only the glass, or fitting a new door leaf into the existing frame, is not providing a controlled fitting and does not need to meet them.
The numbers your doors must meet
| Requirement | Standard | Where it comes from |
|---|---|---|
| Thermal performance (door more than 60% glazed) | U-value 1.4 W/m²K, or Doorset Energy Rating Band C or better | Approved Document L, Table 4.2 |
| Draught-proofing | Units draught-proofed, with insulated cavity closers where appropriate | Approved Document L, paragraph 10.3 |
| Glazing in doors | Safety glass, or otherwise protected, in doors and side panels within 1500mm of the floor | Approved Document K |
| Glazing in an extension | No more than 25% of the extension floor area, plus the area of windows and doors it covers | Approved Document L, paragraph 10.7 |
Most aluminium bifolds sold for UK homes are double or triple glazed to meet 1.4 comfortably. Ask the supplier for the whole-unit U-value, not the centre-pane figure, which is always lower and is not the number building control looks at. For listed or historic buildings where a modern unit would harm the character, Approved Document L allows a centre-pane U-value of 1.2 W/m²K instead.
A new edition of Approved Document L takes effect on 24 March 2027, but the limits for replacement doors in existing homes are not changing.
Route 1: replacing doors in the same opening
Swapping old French doors or patio doors for bifolds in the same-width opening is the simple case. If the installer is registered with a competent person scheme for windows and doors, such as FENSA or Certass, they certify that the work complies and notify the council for you. You should receive a certificate within a few weeks; keep it, as your buyer’s solicitor will ask for it when you sell.
If the installer is not registered, you must apply to building control yourself, usually by building notice, before the work starts. Doors fitted without either route can leave you needing a regularisation certificate later.
Route 2: widening an opening or making a new one
Bifolds look best across a wide span, so most projects widen the existing opening, often turning a window into doors or knocking through to a kitchen extension. That is structural work: a new lintel or steel beam has to carry the wall above, and it needs a structural engineer’s calculations and building control approval under Part A. The doors themselves then get signed off as part of that application rather than through the installer’s scheme. Our page on removing a load-bearing wall covers the beam, the calculations and the party wall side if the opening is near a neighbour’s wall.
Bifolds in an extension: the 25% rule
Large glazed rear extensions are where bifolds most often meet the regulations. Approved Document L limits the total area of windows, doors and rooflights in an extension to 25% of the extension’s floor area, plus the area of any existing windows and doors that the extension covers up. A 4m by 5m extension (20m²) that covers a 3m² patio door could have about 8m² of glazing before the limit bites. Go over it and you need to show the extension performs as well as a compliant one overall, usually with an area-weighted U-value calculation or SAP assessment, which can mean better insulation in the walls or roof to compensate.
Safety glass and escape
Approved Document K treats glazing in a door between the floor and 1500mm above it as a critical location, and in a bifold that is most of the glass, so in practice every pane is specified as safety glass, toughened or laminated, and marked to show it. See safety glass regulations for the zones and markings. Where the bifolds open from a room that relies on them as a way out in a fire, such as an open-plan ground floor, building control may look at the escape route too; our page on open-plan kitchen fire regulations explains when.
Ventilation
Bifolds rarely carry trickle vents, and they are not the main way rooms are ventilated. But if the doors replace windows that had background ventilators, or the room relies on them, building control or the installer will want to see ventilation kept at least as good as before. See trickle vents regulations.
Planning permission
For most houses in England, replacing rear doors with bifolds, or creating a new opening at the back, is permitted development and needs no planning application. You will need to check first if the house is listed (listed building consent is required for almost any alteration), in a conservation area with an Article 4 direction, or if permitted development rights were removed when the house was built. Flats have no householder permitted development rights, and a leaseholder will also need the freeholder’s consent; see licence to alter.
Checklist before you order
- Decide whether the opening stays the same width or gets wider.
- If it gets wider, appoint a structural engineer and apply to building control before work starts.
- Ask for the whole-unit U-value or Doorset Energy Rating in writing.
- Confirm the installer’s scheme membership if it is a like-for-like swap.
- In an extension, add up the glazing against the 25% allowance early.
- Check planning and lease restrictions for flats, listed buildings and conservation areas.
Sources: Approved Document L, Volume 1: Dwellings (2021 edition incorporating 2023 amendments), GOV.UK; Approved Document K, GOV.UK; The Building Regulations 2010, regulation 2 (controlled fitting). Checked 26 October 2026. Every building is different: confirm requirements with your building control body. More on the Vertigo Interiors homepage.
Frequently Asked Questions
Do bifold doors need building regulations approval?
Yes, in the sense that a new or replacement bifold doorset is a controlled fitting and must meet the energy rules. If a FENSA, Certass or similar registered installer fits it in an existing opening, they self-certify and you do not apply to building control. A new or widened opening needs building control approval because of the structural work.
What U-value do bifold doors need?
In an existing home, Approved Document L sets a limit of 1.4 W/m²K for a door with more than 60% of its internal face glazed, or a Doorset Energy Rating of Band C or better. The same 1.4 limit applies to new doors in an extension.
Do I need planning permission for bifold doors?
Usually not for a house, where replacing doors or creating a new opening at the back is normally permitted development. Flats, listed buildings and houses in conservation areas or with permitted development rights removed are different, so check with the council first.
Do bifold doors need safety glass?
Yes. Glazing in doors and in side panels within 1500mm of floor level is a critical location under Approved Document K, so it must be toughened or laminated safety glass, or otherwise protected.
Is there a limit on how much glazing an extension can have?
Approved Document L says glazing in an extension, including bifolds and rooflights, should not exceed 25% of the extension’s floor area plus the area of any windows and doors it covers up. Above that, you need to show the extension performs as well overall, usually with a calculation.