Replacement windows, and external doors that are more than half glazed, must meet the Building Regulations. That means Part L energy limits, at least the same ventilation and means of escape as before, and safety glass in critical areas. The work is certified by a registered installer, through a scheme such as FENSA or CERTASS, or by building control.
Do replacement windows need Building Regulations approval?
Yes. In England, replacing a whole window, roof window or rooflight, or an external door that is more than half glazed, counts as building work and must comply with the Building Regulations. GOV.UK says external doors that are less than half glazed don't need approval, although they should still be fitted properly. There are two ways to show that windows comply:
- Use an installer registered with a competent person scheme for windows and doors. They certify the work themselves and register it with building control.
- Or apply to a building control body, either the council or a private approver, before the work. It inspects the installation and issues a certificate.
- Either way you should get a certificate. FENSA and CERTASS are two of the government-authorised schemes for replacement windows and doors. A registered installer must give you a certificate and notify building control within 30 days of finishing. If nothing has arrived after 30 days, contact the scheme operator.
What does Part L require for replacement windows and doors?
Part L of the Building Regulations limits heat loss, measured as a U-value: the lower the number, the less heat escapes. A new edition of Approved Document L was published in March 2026 and is due to take effect in 2027. Industry guidance so far indicates the standard for replacement windows is unchanged, with the main changes aimed at new homes. For new or replacement units in an existing home in England, the current limits are:
- Windows and roof windows: a U-value of 1.4 W/m²K or better, or a Window Energy Rating of band B or better.
- External doors with more than 60% of the internal face glazed: 1.4 W/m²K, or a Doorset Energy Rating of band C or better.
- Other external doors: 1.4 W/m²K, or a Doorset Energy Rating of band B or better.
- Rooflights: 2.2 W/m²K.
Do my new windows need trickle vents?
Trickle vents are small slotted vents, usually in the top of the frame, that let a little fresh air in while the window is shut. Approved Document F, which covers ventilation, says:
- If your existing windows have trickle vents, the new ones must have them too. They must be no smaller than before and must be controllable.
- If your existing windows don't have them, the new windows mustn't leave the house less well ventilated than before. Fitting trickle vents is the usual way to show this: at least 8,000 mm² equivalent area in habitable rooms and kitchens, and 4,000 mm² in bathrooms.
- In some homes there are alternatives, such as continuous mechanical extract ventilation or existing wall vents that are big enough, but these need to be agreed with building control. Trickle vents can be closed, and they help prevent condensation and mould once draughty old windows are replaced with airtight ones.
What about fire escape windows and safety glass?
A replacement window must give at least the same means of escape as the one it replaces. Where a window is needed for escape, the opening part should give a clear area of at least 0.33 m², at least 450 mm wide and 450 mm high, with the bottom of the opening no more than 1,100 mm above the floor. Ask which of your windows are escape windows before the order is placed.
Safety glass is needed in 'critical locations' where people could fall against or walk into the glass. These include any glazing within 800 mm of the floor, glazing in doors up to 1,500 mm from the floor, and side panels within 300 mm of a door edge.
Do I need planning permission for new windows or doors?
Usually not. Replacing windows and doors with ones of a similar appearance to those on the house is normally permitted development. The exceptions are:
- Listed buildings, where you need listed building consent for significant works, inside or out.
- Conservation areas and areas covered by an Article 4 direction, where extra restrictions may apply, particularly to windows and doors facing the street.
- Flats and maisonettes, where you should check with the council, and with the freeholder if you are a leaseholder.
- New bay windows, which are treated as extensions and may need permission.
- New upper-floor windows in a side wall or roof slope, which must be obscure-glazed and non-opening unless the opening part is more than 1.7 m above the floor.
How much do replacement windows and doors cost?
Prices depend on the number and size of openings, the frame material and style, and how easy the old frames are to remove. These are typical 2026 West Midlands ranges, including VAT, removal of the old frames and certification. Bays, sash styles, coloured or woodgrain finishes, triple glazing and awkward access all push prices up. Most whole-house installations take two to four days on site, after a manufacturing lead time of a few weeks.
- A single white uPVC casement window, supplied and fitted: around £380–£650.
- All the windows in a typical three-bedroom semi, around 8–10 openings, in white uPVC: around £3,800–£6,500.
- A composite front door in a standard frame, supplied and fitted: around £1,100–£1,750, or £1,800–£3,400 with side panels.
Why does the window certificate matter?
The FENSA, CERTASS or building control certificate is your proof that the windows comply. When you sell, the buyer's solicitor will usually ask for it for any windows replaced while you owned the house, and a missing certificate can delay the sale. FENSA's own guidance says that if an installer doesn't offer a compliance certificate, you'll need to pay for a building control inspection. If you lose a certificate, the scheme the installer used can usually supply a replacement, sometimes for a small fee.
Before you sign a window or door quote, ask which scheme the installer is registered with for this type of work, who registers the job, the U-value or energy rating of the units quoted, whether trickle vents are included, which windows will be escape windows, and what manufacturer's guarantee terms apply to the frames and glass. The answers should be in writing.
Sources
- Planning Portal – Doors and windows: building regulations
- Planning Portal – Doors and windows: planning permission
- GOV.UK – Approved Document L, Volume 1: Dwellings, 2021 edition incorporating 2023 amendments
- GOV.UK – Approved Document F (ventilation), Volume 1: Dwellings, 2021 edition
This guide is general information for homes in England, not legal or professional advice for your property. Rules change — check with your council or the Planning Portal before you rely on it.