Entry 03 · Windows & Glazing
Approved Document L for replacement windows
Understand Approved Document L for replacement windows, covering U-values, energy efficiency duties and compliance checks in England homes today.
Approved Document L sets the energy rules that underpin a window replacement in England, and your project as a homeowner usually falls within the dwellings volume. You will see which document to open, how start dates determine the edition, and where the official page stays silent on window detail.
When you replace sealed units or whole frames in a house or a flat, you are not only choosing glass and frames for light and draughts. You are doing building work that touches the energy performance of an existing building, and Part L of Schedule 1 to the Building Regulations provides the legal framework for that work. Approved Document L gives the technical guidance that explains how to meet those energy efficiency requirements in practice.
The source page applies to England only. It does not describe planning permission for extensions or listed buildings, and it does not name products or installers. It points you to two technical volumes, one for dwellings and one for buildings other than dwellings, plus later amendments and a newer 2026 pair for buildings subject to the 2026 standards.
01 What the rule covers in plain terms
The page holds the current guidance covering the energy efficiency requirements of the building regulations as set out in Part L of Schedule 1 and in a number of specific building regulations. That wording matters for you because it shows the hierarchy. The regulation sets the duty, the Approved Document shows accepted ways to meet it, and your window choice has to sit inside that structure rather than beside it.
For a homeowner this means heat loss through the building fabric is the concern behind the text. Windows and glazed doors let in daylight and give ventilation, yet glass and frame joints also let heat pass out in winter. The guidance exists to keep that balance toward lower energy use across new and existing buildings, which is why replacement work in an older semi or terrace is still in scope even when the wall structure stays untouched.
02 Which volume applies to your house?
Current technical guidance is contained in two documents. Approved Document L, Conservation of fuel and power, Volume 1: Dwellings covers houses and flats, so it is the volume you open first for a home window project. The reference edition on the page is the 2021 edition incorporating 2023 amendments, with reference ISBN 978-1-914124-78-5, published as a PDF of 1.44 MB and 104 pages.
Approved Document L, Conservation of fuel and power, Volume 2: Buildings other than dwellings sits alongside it for shops, offices and other non-domestic stock. The reference edition is the 2021 edition incorporating 2023 amendments, with reference ISBN 978-1-914124-79-2, published as a PDF of 1.35 MB and 116 pages. A separate February 2023 amendments file of 129 KB and 6 pages records small changes to both volumes, and archived versions of previous editions are held on the National Archives for older work.
03 What does the 2026 edition change for you?
The page lists a newer pair under the heading Approved Document L (2026). It says that pair provides guidance on meeting the energy efficiency requirements of Part L for buildings subject to the 2026 standards. The two items are Approved Document L: Energy and greenhouse gas emissions, Vol 1: Dwellings (2026 edition) and Approved Document L, Volume 2: Buildings other than dwellings (2026 edition).
You can check the scope and file list on the official Approved Document L page before you download a PDF for your project dates. The page adds one guardrail that helps you avoid using the wrong year. Earlier versions of Approved Document L continue to apply to buildings subject to previous regulatory standards, so the correct edition follows the regulatory standard for your building work rather than the newest file on the screen.
04 Why does energy performance shape a window choice?
Glass area affects daylight and solar gain, frame material affects airtightness around the opening, and the junction with the wall can cause ongoing heat loss if seals fail. The regulation looks at the building as a heated space, so a change from single glazing to double glazing, or from an old double-glazed unit to a modern sealed unit, alters how that heated space holds warmth. If you follow how glass ratings and heat loss values work, you see why the guidance treats windows as part of fabric efficiency rather than as decoration.
The official page itself does not publish a U-value figure, a window energy rating band, or a product comparison. The page does not publish a cost, a payback period, or a recommendation between uPVC and timber. That silence is useful. It tells you to read the relevant volume for the method and to keep product claims separate from regulatory guidance, then compare frames on maintenance and lifespan with the data from the maker.
05 How do start dates decide which guidance applies?
The Amendment Regulations and accompanying Approved Documents L: Volumes 1 and 2 come into force on 15 June 2022. The page then sets a transitional rule. The changes will not apply in relation to building work where a building notice or an initial notice has been given to, or full plans deposited with, a local authority before 15 June 2022 provided that the building work is started before 15 June 2023.
Three terms in that sentence carry legal weight. The page notes that building notice, initial notice and full plans have the meanings given in Regulation 2 of the Building Regulations 2010, so a letter or phone call does not count unless it meets those definitions. Where an application covers several buildings on one site, for example, several houses, only those individual buildings for which work is commenced can take advantage of the transitional provisions.
06 Who keeps the guidance under review?
Since April 2023, the Building Safety Regulator has a duty under the Building Safety Act 2022 to keep under review the safety and standards of all buildings in England, which includes advising government on updates to the Approved Documents. In plain terms, the technical detail is not frozen. A body with a statutory duty watches how the stock performs and advises on revisions, and the page history shows how that advice turns into published corrections.
The update list on the page records republication on 15 June 2022 to correct a minor misprint and to mark the new documents coming into force, republication on 25 February 2022 with corrections found in a circular, first addition of the two volumes on 15 December 2021, and addition on 2 February 2023 of the 2021 editions incorporating 2023 amendments. For printed research, the page names RIBA books as the online seller for printed copies.
07 How should you read the page before you sign?
Treat the official page as a map rather than a manual for your bay or sash. Open Volume 1 for dwellings, check the ISBN and page count so you know you hold the 2021 edition incorporating 2023 amendments unless your work falls under the 2026 standards, and read the February amendments file alongside it. If your home falls under controls for appearance or structure, use the Planning Portal to find planning and building guidance and, where needed, to apply online for planning permission or make a building control application.
Then translate what you read into questions about the opening itself. Ask what part of the wall build-up will be disturbed, how the new frame will be sealed to the reveal, and which paperwork will record the edition you relied on. If you keep sale paperwork in one folder, file the volume reference next to the certificate file you keep after replacement so a future buyer sees the regulatory basis without hunting through downloads.
About the GOV.UK source page
The GOV.UK page titled Conservation of fuel and power: Approved Document L is building regulation guidance for England on energy performance of new and existing buildings. It gives access to Volume 1: Dwellings and Volume 2: Buildings other than dwellings, the February 2023 amendments file, the 2026 editions list, transitional arrangements, archived editions, and the page update history.
Download the PDF that matches your start date, note its ISBN, page count and amendment file, then write that reference on your quote comparison sheet before you accept a window specification.