In England, a replacement sliding door is a controlled fitting under the Building Regulations, so it must either be fitted by an installer registered with a competent person scheme or be notified to Building Control. Forming or widening an opening is structural work and needs a Building Regulations application of its own.
The rules differ across the UK. Wales has its own energy guidance, Scotland uses building warrants and building standards, and Northern Ireland has its own regulations run by district councils. This guide sets out the position nation by nation, then explains why the certificate matters when you sell. It is general guidance, so check the current rules for your property before work starts.
What are the rules in England?
Replacement doors are controlled fittings, which means the work has to meet the Building Regulations and someone has to confirm that it does. There are two routes:
- Competent person scheme. An installer registered with a scheme self-certifies the work and notifies it, and you receive a certificate.
- Building Control. The work is notified to Building Control, which checks it and confirms compliance when it is satisfied.
On a sliding door replacement with us, compliance is arranged through a competent person scheme installer or by notifying Building Control, and the route is stated in your quote. Three Approved Documents matter most for the door itself, covered below.
If you buy a door supply only, the person who fits it is responsible for compliance. Before you book them, check whether they are registered with a competent person scheme or will notify Building Control, and agree who pays any Building Control fee. A door fitted with no notification at all leaves you without the paperwork a buyer will later ask for.
What U-value does a sliding door need in England?
Under Approved Document L (2021 edition), a new or replacement door in an existing home with more than 60% glazing must achieve a U-value of 1.4 W/m²K or better. Almost every sliding door is more than 60% glass, so this is the figure that applies. A lower U-value means less heat lost through the door.
The figure is for the whole door, frame and glass together, not the glass alone. Good thermally broken aluminium double glazed sliders typically achieve around 1.2–1.6 W/m²K depending on the system, so the system and glass have to be chosen to reach 1.4 or better. Triple glazed sliders typically reach around 0.8–1.1 W/m²K, which is worth considering for large north-facing doors; see triple glazed sliding doors.
What about safety glass and security?
Under Approved Document K, glazing in doors is in a critical location, so it must be safety glazing: toughened or laminated glass classified to BS EN 12600. That applies to every pane in a sliding door. Toughened glass breaks into small, blunt pieces; laminated glass holds together when broken because of its plastic interlayer, which also helps with security.
Approved Document Q sets security requirements for doors and windows in new dwellings. It does not apply when you replace a door in an existing home, so on a replacement the level of security is your choice. Systems are available tested to PAS 24, the UK enhanced security test standard for doorsets. If you are building a new home, including a self-build, tell us at the start so the door is specified to suit.
What if I am forming or widening an opening?
Forming a new opening or widening an existing one changes the structure of the house, so in England it needs a Building Regulations application, structural calculations and usually a steel beam or lintel. Building Control checks the calculations and inspects the work as it goes, then issues a completion certificate.
This is separate from the door, which is still a controlled fitting in its own right. Our guide to widening an opening covers the process, and planning is a separate question again.
What are the rules in Wales?
Wales has its own Building Regulations guidance, including its own Approved Document L (Wales) for energy efficiency. Do not assume the English figures apply: Welsh requirements are set separately and can change on a different timetable.
Check the current guidance on GOV.WALES or ask your local authority building control, and make sure your installer confirms in writing how compliance will be shown for your door. Wales also has its own planning rules, covered in our planning permission guide.
What are the rules in Scotland?
In Scotland, a like-for-like door replacement in a house usually does not need a building warrant, but the work must still meet the Scottish building standards, including those for energy and safety. The new door therefore still has to be specified to current standards even though no warrant is issued.
Forming or widening an opening needs a building warrant before work starts. Applications go to your local council's building standards service, and the Scottish Government's building standards pages explain how the system works.
What are the rules in Northern Ireland?
Northern Ireland has its own Building Regulations (Northern Ireland), administered through district council building control. Energy efficiency guidance is set out in Technical Booklet F1, which is separate from the English Approved Documents.
Ask your council's building control service what applies to your door, and to any structural work, before you order. Work in Northern Ireland is by arrangement, so tell us early if your property is there.
Why does the certificate matter when you sell?
When you sell, the buyer's solicitor will usually ask for evidence that replacement doors and any structural work met the Building Regulations. In England that means the competent person scheme certificate for the door, or confirmation from Building Control, plus the completion certificate for any new or widened opening.
Missing paperwork can hold up a sale or lead the buyer to ask for extra assurances before exchange. If you are buying a home with newer sliding doors, ask the seller for the same paperwork. Keep these together with your property documents:
- The competent person scheme certificate, or Building Control's confirmation, for the door
- The completion certificate for any new or widened opening, with the structural calculations
- Your written quote and the product details, including the whole-door U-value and glass type
- The manufacturer guarantee documents for the frame, hardware and sealed units
Common questions
Do I need Building Regulations approval to replace a patio door?
In England, yes: a replacement door is a controlled fitting. Either an installer registered with a competent person scheme self-certifies and notifies the work, or the work is notified to Building Control. You do not normally make a separate application yourself when a registered installer is used. Scotland, Wales and Northern Ireland have their own rules.
What U-value does a sliding door need?
In England, Approved Document L requires a new or replacement door in an existing home with more than 60% glazing to achieve a U-value of 1.4 W/m²K or better, measured for the whole door. Wales, Scotland and Northern Ireland set their own energy requirements, so check the guidance for where you live. Your quote should state the whole-door U-value of the door being supplied.
Does a sliding door need toughened glass?
It needs safety glass. Under Approved Document K in England, glass in doors is in a critical location, so it must be toughened or laminated safety glazing classified to BS EN 12600. Both types count. Laminated glass holds together when broken, so it is often used for the inner pane where security matters.
What if I cannot find the certificate for my doors?
Start with the installer, or the competent person scheme they used, which may hold a record of the work. For structural work, ask Building Control for a copy of the completion certificate. If nothing can be found, your solicitor can advise on the options, so it is worth checking well before you put the house on the market.
Sources and further reading
- Building regulations approval (GOV.UK)
- Competent person schemes: current schemes and how they are authorised (GOV.UK)
- Approved Document L: conservation of fuel and power (GOV.UK)
- Approved Document K: protection from falling, collision and impact (GOV.UK)
- Approved Document Q: security in dwellings (GOV.UK)
- Building regulations in Wales (GOV.WALES)
- Building standards in Scotland (gov.scot)
- Building Control Northern Ireland (nidirect)
- Building Regulations in Northern Ireland, including Technical Booklets (Department of Finance NI)