Future Homes and Buildings Standards from 24 March 2027: What the 2026 Approved Document L Says About Windows and Doors in England

The Building Regulations etc. (Amendment) (England) Regulations 2026 come into force on 24 March 2027, and a new 2026 edition of Approved Document L Volume 1 (dwellings) takes effect on the same date for building work that is not higher-risk building work. For a housing project in England that will buy windows and doors from China, this decides which U-value limits, which test or calculation method and which installation guidance the building control body will use.

This guide reads the primary texts: the statutory instrument, the Ministry of Housing, Communities and Local Government (MHCLG) circular letter of 24 March 2026, and the 2026 edition of Approved Document L Volume 1, which we read on 7 October 2026. It covers England and dwellings only, it is a reading guide and not building control advice, and it does not compare the 2026 edition with earlier editions, because we did not read an earlier statutory edition for this guide.

When do the new rules apply, and to which projects?

Regulation 1 of SI 2026 No. 335 says the Regulations come into force on 24 March 2027, except that regulations 3, 4, 6, 7, 8 and 9 come into force for higher-risk building work and work to existing higher-risk buildings on 24 September 2027. The Regulations extend to England and Wales and apply to buildings and building work in England. The 2026 edition of Approved Document L Volume 1 states the same two dates on its second page.

The MHCLG circular letter describes the transitional arrangements. For work that is not higher-risk building work, the changes do not apply to work on a building where a building notice, an initial notice, or an application for building control approval with full plans was given to the relevant authority before 24 March 2027, provided the building work is commenced before 24 March 2028. Separate arrangements apply to higher-risk building work. The letter notes that other earlier transitional arrangements can also continue to apply.

For a procurement team, the point is practical: which edition governs a given block or phase depends on when the notice or application was given and when work starts. Ask the architect or building control body which edition applies to each phase before the window and door specification is fixed, and put that answer in the brief.

How must a window or door U-value be shown?

Paragraph 3.1 of the 2026 edition says U-values should be assessed using the methods and conventions in the Building Research Establishment’s BR 443, for the whole fabric element, which for a window means the combined performance of glazing and frame. For new dwellings, paragraph 3.2 says the U-value of a window or door should be determined by one of two routes: measured using the hot-box method in BS EN ISO 12567-1 for windows (BS EN ISO 12567-2 for roof windows), or calculated using the actual size and configuration of the window in line with BS EN ISO 10077-1 and BS EN ISO 10077-2.

Paragraph 3.3 says that for new dwellings the determination is to include, where present, the actual frame sections, sills and thresholds, add-ons and frame extenders, dummy sashes, dummy transoms and mullions, decorative glazing bars within the glazing unit cavity, and non dead-load-bearing coupling components, and to exclude dead-load-bearing items such as bay poles. A U-value quoted for a standard test size or for the glass alone therefore does not answer the question the text asks.

Paragraph 3.6 adds that the U-value must be calculated for the element in the appropriate plane: vertical for windows and roof windows, horizontal for rooflights, with data for the wrong plane adjusted following BR 443. Ask the maker for the calculation or test report for the exact product configuration on your schedule, in the form paragraphs 3.2 and 3.3 describe.

What limiting values does the 2026 edition list for new dwellings?

Table 3.1 of the 2026 edition, “Limiting U-values for new fabric elements and air permeability in new dwellings”, lists a maximum U-value of 1.6 W/(m²·K) for windows (including roof windows and curtain walling), 2.2 for rooflights, and 1.6 for doors including glazed doors. The table’s first note says the values are area-weighted average values. Note 4 says that if other performance, such as wind load, safety, security or acoustic attenuation, requires thicker glass, an equivalent window unit with standard 6 mm glazing should be shown to meet the required standard.

Paragraph 3.7 says insulating fabric elements in new dwellings should meet the limiting standards in Table 3.1, and a further note below the table says that to meet the target fabric energy efficiency rate in Section 1 the energy efficiency of some elements will need to be significantly greater than the limiting standards. Treat Table 3.1 as the floor for the window and door schedule, not as the design target.

The same document is guidance, not the regulation itself, and the edition that applies to your project is decided by the transitional rules above. Confirm the values against the edition your building control body names.

What changes when you replace or add windows and doors in existing dwellings?

Table 3.2 sets limiting values for new fabric elements in existing dwellings: windows at 1.4 W/(m²·K) or Window Energy Rating Band B minimum; doors with more than 60% of the internal face glazed at 1.4 or Doorset Energy Rating Band C minimum; other doors at 1.4 or Doorset Energy Rating Band B minimum; rooflights at 2.2; and a maximum of 1.8 permitted for external fire doorsets as defined in Approved Document B Volume 1. Paragraph 3.9 adds that a replacement element’s U-value should be no higher than that of the element being replaced and should also meet Table 3.2.

Paragraph 10.3 says that for new and replacement windows, roof windows, rooflights and doors (controlled fittings), if the entire unit is provided, units should be draught-proofed, meet the Table 3.2 standards, and have insulated cavity closers installed where appropriate. Paragraph 10.4 says building control bodies may accept a Window Energy Rating or Doorset Energy Rating from a certification scheme that provides a quality-assured process and audit trail from calculation through to installation. Paragraph 10.6 says replacing glazing, or replacing a window or door in its existing frame, is not providing a controlled fitting and does not need to meet these energy efficiency requirements.

These paragraphs matter mainly for refurbishment and conversion packages. For a related case, see our guide to office-to-residential conversions.

What does the guidance say about installation?

The 2026 edition’s guidance on building and installing the thermal envelope says windows and doors should be installed so that the thermal integrity of the insulated plane is maintained. It says tolerance around a unit and its opening should be minimal and in accordance with BS 8213-4, that windows should overlap the inner face of the external leaf by 30 mm to 50 mm and doors by 50 mm so that the unit is contiguous with the insulation layer of the wall, and that fully insulated and continuous cavity closers should be used. For doors, perimeter insulation should be installed in the threshold zone or a reinforced cavity closure used.

On airtightness, the same document says window and door units should connect to the primary air barrier and frames should be taped to the surrounding structural openings using air-sealing tape, with compressible seals or gun sealant used to supplement taping. Those are site details, but they affect what a maker should supply: frame depth and sill or threshold details need to be drawn to suit the wall build-up. For overheating in new dwellings, paragraph 0.27 sends readers to Approved Document O, so glazing area and solar control are not settled by Approved Document L alone.

What to put in a window and door enquiry for an England housing project

• Edition and phase: state which Approved Document L edition applies to each block or phase, as confirmed by the architect or building control body.
• Product schedule: list every window and door type with sizes, configuration, opening type and glazing, so a U-value can be tied to each.
• U-value evidence: ask for a hot-box test report or a calculation for the exact configuration, in the form paragraphs 3.2 and 3.3 describe, and for the plane the element is installed in.
• Energy rating route: for replacement work, ask whether the maker’s Window Energy Rating or Doorset Energy Rating comes from a certification scheme the building control body will accept.
• Thicker glass: if wind, safety, security or acoustic needs require thicker glass, ask for the equivalent-unit evidence that note 4 describes.
• Installation details: ask for frame depth, sill and threshold details and cavity closer proposals drawn against the wall build-up.
• Documents with the shipment: ask what test or calculation documents and product marking will travel with the goods, so site staff can match them to the schedule.

Next steps for a UK housing window package

Send each maker the same schedule and ask for the evidence above in writing. For the market-specific marking rules, see our guide to UKCA versus CE marking, and for the supply side see our guide to aluminium window and door manufacturers for UK and European projects. FBM Sourcing also runs FBM Furniture’s compliance pages for furniture-only packages; windows and doors stay on this site.

Questions buyers ask about windows and doors under the 2026 Approved Document L

When does the 2026 edition of Approved Document L Volume 1 take effect?

The document states that it takes effect on 24 March 2027 in England for building work that is not in connection with higher-risk building work, and on 24 September 2027 for work in connection with higher-risk building work. Transitional arrangements are set out in MHCLG Circular Letter 01/2026.

Does a project that has already given a building notice or full plans have to follow the new edition?

The circular letter says that for work that is not higher-risk building work, the changes do not apply where a building notice, initial notice or full plans application was given before 24 March 2027 and the work is commenced before 24 March 2028. Ask the building control body to confirm how this applies to your phases.

How should the U-value of a new window be determined for a new dwelling?

Paragraph 3.2 allows either a hot-box measurement under BS EN ISO 12567-1 (roof windows 12567-2), or a calculation using the actual size and configuration under BS EN ISO 10077-1 and 10077-2, including the items listed in paragraph 3.3.

Is replacing glazing in an existing frame covered by the window standards?

Paragraph 10.6 says replacing glazing, or replacing a window or door in its existing frame, is not providing a controlled fitting and does not need to meet the energy efficiency requirements. Replacing the entire unit including the frame does.

How does FBM Sourcing support a window and door package?

We review the brief, collect comparable quotations and manage the package for the project. For suppliers you nominate, we charge a 5% commission; for products we source for you, we quote a direct price. Our own team performs one inspection after bulk production is complete and before shipment, and the client’s project team is welcome to attend.

FBM Sourcing manages the entire China procurement package for overseas construction projects. We work with Developers · General Contractors · Builders · Commercial Project Owners · Interior Design & Construction Companies · FF&E Solution Providers.