Replacing a complete window or external door, including its frame, is controlled by building regulations in every UK nation. The new window must meet standards for energy performance, ventilation, means of escape and safety glazing. How the work is approved differs: England and Wales use competent person schemes or building control, Scotland needs no warrant but full compliance, and Northern Ireland exempts dwellings from applications.
Do building regulations apply to replacement windows?
Yes. Building regulations apply to replacement windows and doors across the UK, but the detail and the approval route differ between England, Wales, Scotland and Northern Ireland. The rules are aimed at whole replacements, where the frame comes out and a new window goes in, because that changes how the opening performs for heat loss, ventilation, fire escape and safety.
Repairs are treated differently. The Planning Portal's guidance for England says building regulations will normally apply when the whole fixed frame and opening parts are replaced, but will not normally apply where the work amounts to no more than replacing broken glass. Replacing a misted sealed unit in a sound frame is therefore usually a repair rather than a new window.
How are replacement windows approved in England?
In England there are two routes. The first is to use an installer registered with a competent person scheme for replacement windows and doors, such as FENSA or Certass. The installer self-certifies that the work complies, the local authority is notified, and the householder receives a certificate. GOV.UK says you do not need to get approval yourself if you use someone registered with a competent person scheme.
The second route is to apply to a building control body, either the local authority or a registered building control approver. For small domestic jobs this is usually a building notice, which allows work to start two days after it is submitted, and the body inspects and issues a completion certificate if satisfied. Either way, keep the certificate, because it will be asked for when the property is sold.
What standards must replacement windows meet in England?
Energy performance is set by Approved Document L, Volume 1, 2021 edition incorporating 2023 amendments, in force since 15 June 2022. For replacement windows in existing dwellings, Table 4.2 sets a limit of 1.4 W/(m²·K), or a Window Energy Rating of Band B or better. Doors have a 1.4 limit or a Doorset Energy Rating of Band C for mostly glazed doors and Band B for others. Rooflights are limited to 2.2.
Ventilation is covered by Approved Document F, Volume 1. If the old windows had trickle vents, the new ones should too, no smaller and controllable. If they did not, ventilation must be no worse than before, and Approved Document F gives minimum trickle vent areas of 8000mm² for habitable rooms and kitchens and 4000mm² for bathrooms, or other provision agreed with building control.
The replacement must also keep at least the same potential for escape as the window it replaces, and glass in critical locations must be safety glazing under Approved Document K. The Planning Portal gives escape window sizes as a clear openable area of at least 0.33m², at least 450mm high and wide, with the bottom no more than 1100mm above floor level.
- Energy: Approved Document L, Volume 1
- Ventilation: Approved Document F, Volume 1
- Safety glazing: Approved Document K, Section 5
- Means of escape and fire spread near boundaries
| Nation | Approval route for a dwelling | Main guidance |
|---|---|---|
| England | Competent person scheme installer, or a building control body (building notice or full plans) | Approved Documents L, F and K |
| Wales | Competent person scheme installer, or a building control body | Welsh Approved Documents L and F, and Approved Document N |
| Scotland | No building warrant to replace a window including its frame, but the work must meet the building standards | Technical handbooks, standards 2.9, 3.14, 4.8 and 6.2 |
| Northern Ireland | No notice or plans for replacement windows or external doors of a dwelling, but the work must comply | Technical Booklets F1, K, E and V |
What are the rules for replacement windows in Wales?
The Welsh Government says building regulations have applied to all replacement glazing in Wales since 1 April 2002. An installer registered with a competent person scheme can do the work without building control involvement, notify the local authority and issue a certificate. Otherwise approval comes from a building control body, which inspects the work and issues a certificate of compliance if satisfied.
Wales publishes its own Approved Documents. Approved Document L, Volume 1, 2022 edition incorporating 2024 amendments, for use in Wales, sets limits for replacement windows of 1.4 W/(m²·K) or Window Energy Rating Band B, with similar limits for doors and 2.2 for rooflights. A new Welsh Approved Document L and Approved Document F, Volume 1, take effect on 4 March 2027, so check which edition applies to your work.
The Welsh Government's guidance also covers means of escape, using the same 0.33m², 450mm and 1100mm escape window criteria, and safety glazing under Approved Document N. For dwellings built from 1999 onwards, a replacement main entrance door should keep its level threshold, so the work does not make access worse than when the home was built.
Do you need a building warrant to replace windows in Scotland?
No, but the work must still comply. In Scotland, schedule 3 to the Building (Scotland) Regulations 2004 lists replacing a door, window or rooflight, where the work includes replacing the frame, as work that does not need a building warrant, on condition that it meets the standards in all respects. Smaller work to a window, including reglazing, must be to a standard no worse than before. Altering the size of the structural opening generally needs a warrant.
The technical handbooks set out how to meet the standards. They include a target U-value for replaced windows, doors and rooflights under standard 6.2, ventilation under standard 3.14, and safety glazing under standard 4.8. The domestic handbook also covers safe cleaning, recommending that windows more than 4m above the adjacent ground can be cleaned safely, for example from inside.
Escape windows are recommended in apartments on upper storeys up to 4.5m above ground unless there is an alternative escape route. The handbook gives an unobstructed openable area of at least 0.33m², at least 450mm high and 450mm wide, with the bottom no more than 1100mm above the floor.
What are the rules for replacement windows in Northern Ireland?
In Northern Ireland, regulation 9 of the Building Regulations (Northern Ireland) 2012 exempts the replacement of windows or external doors of a dwelling from the need to give notice or deposit plans with the council. The same regulation says the replacement work must in all respects meet the relevant requirements of the regulations, so the exemption removes the application, not the standards.
The Department of Finance publishes the technical booklets that explain those requirements. Technical Booklet F1 (June 2022) covers conservation of fuel and power in dwellings, Technical Booklet K covers ventilation, Technical Booklet E covers fire safety and Technical Booklet V covers glazing. For buildings other than dwellings, ask the council's building control team whether an application is needed.
Do you need planning permission or other consents as well?
Building regulations and planning are separate. In England, the Planning Portal says new windows and doors of a similar appearance to those used in the house usually do not need planning permission, but permitted development rights can be removed by an Article 4 Direction, and conservation areas may have extra controls. Flats, leasehold homes and commercial premises can also have their own restrictions.
Listed buildings need listed building consent for works affecting their character, inside or out, in every UK nation, and Historic England notes that this can include replacing windows. Applications go to the local planning authority, or the council in Northern Ireland. Cadw advises that replacing traditional windows in a listed building with uPVC will not normally be acceptable in Wales.
What paperwork should you get after replacement windows are fitted?
In England and Wales, you should receive either a competent person scheme certificate from a registered installer or a completion certificate from a building control body. Keep it with your property documents. Buyers' solicitors commonly ask for evidence that replacement windows were installed in line with building regulations.
In Scotland and Northern Ireland, there is no warrant or application for straightforward window replacement in a dwelling, but the work must still meet the standards. Ask the installer to confirm in writing the energy performance, safety glazing and ventilation provided. Our written quotes list the specification for each window, and guarantee terms are set out in writing with your quote.
Frequently asked questions
Do I need building regulations approval to replace my windows?
The work must comply with building regulations everywhere in the UK, but the approval process varies. In England and Wales, a competent person scheme installer can self-certify, or you apply to building control. In Scotland, no building warrant is needed to replace a window including its frame. In Northern Ireland, dwellings are exempt from making an application.
What is a FENSA or Certass certificate?
FENSA and Certass are competent person schemes for replacement windows and doors in England and Wales. An installer registered with a scheme can self-certify that the work meets building regulations, and the installer or scheme notifies the local authority and provides a certificate. Keep the certificate with your property documents, as solicitors usually ask for it on a sale.
Do replacement windows need trickle vents?
In England, Approved Document F says that if the old windows had trickle vents, the new ones should have them too, at least as large and controllable. If they did not, ventilation must be no worse than before, typically by fitting trickle vents. Wales, Scotland and Northern Ireland have their own ventilation guidance, so confirm what applies to your property.
Can a replacement window be smaller than the old one?
It depends on the window's role. In England and Wales, guidance says a replacement should provide at least the same potential for escape as the window it replaces, so an escape window should not be made smaller than the minimum sizes. Reducing the structural opening can also affect ventilation and daylight, and in Scotland altering the opening generally needs a building warrant.
Do replacement doors have to meet building regulations?
Yes, external doors are covered as well as windows. In England, Approved Document L sets a limiting U-value of 1.4 W/(m²·K) for replacement doors in existing dwellings, with an alternative Doorset Energy Rating, and glazing in doors must be safety glass. Wales has similar limits. Scotland and Northern Ireland apply their own handbooks and technical booklets.
Sources
- Doors and windows: building regulations – Planning Portal
- Approved Document L, Volume 1: Dwellings, 2021 edition incorporating 2023 amendments – GOV.UK
- Approved Document F, Volume 1: Dwellings – GOV.UK
- Building regulations: doors and windows – GOV.WALES
- Approved Document L: conservation of fuel and power – GOV.WALES
- Building standards technical handbook 2022: domestic – 0.5 work not requiring a warrant – gov.scot
- The Building Regulations (Northern Ireland) 2012, regulation 9 – legislation.gov.uk
- Building regulations technical booklets – Department of Finance NI
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