Part L and the Future Homes Standard

What do Part L and Approved Document L require in 2026?

Part L of the Building Regulations 2010 sets the energy efficiency standards for new and existing buildings in England, and Approved Document L is the statutory guidance on meeting it. Most projects are designed to the 2021 edition today, but a 2026 edition implementing the Future Homes and Buildings Standards comes into force on 24 March 2027, or 24 September 2027 for higher-risk building work.

That makes October 2026 a transition year. A project being designed now may be built under either standard, depending on when the building control application goes in and when work starts.

Part L sits in Schedule 1 to the Building Regulations 2010. Requirement L1 currently requires reasonable provision for the conservation of fuel and power: limiting heat gains and losses through the fabric and from pipes, ducts and vessels, and providing fixed building services that are energy efficient, have effective controls and are properly commissioned. Requirement L2 covers on-site electricity generation.

Part L is supported by a group of regulations, including the energy performance targets for new buildings (regulations 24 to 27), consideration of high-efficiency alternative systems (regulation 25A) and the provision of information (regulation 40).

Volume 1 vs Volume 2

Volume 1 covers dwellings and work to existing dwellings. Volume 2 covers buildings other than dwellings. Both are currently the 2021 edition incorporating 2023 amendments, and both are replaced by 2026 editions from 24 March 2027.

How new homes comply with the 2021 edition

The 2021 edition came into force on 15 June 2022. A new dwelling has to pass four tests: three calculated rates set by a notional dwelling, plus minimum standards for fabric and fixed building services.

When it was announced, the government said CO2 emissions from new homes would be around 30% lower than under the previous standard, and 27% lower for other new buildings including offices and shops. The four tests in Volume 1 are:

1. Target primary energy rate (kWhPE/m² per year): the dwelling primary energy rate must not exceed the target set by the notional dwelling.
2. Target emission rate (kgCO2/m² per year): the dwelling emission rate must not exceed the target.
3. Target fabric energy efficiency rate (kWh/m² per year).
4. Minimum standards for fabric and fixed building services.

Two evidence requirements that changed site practice

• BREL reports: a design stage and an as-built Building Regulations England Part L report, with the as-built version signed by the energy assessor and the developer.
• Photographic evidence: photographs for each dwelling of key junctions and details, including foundations, walls, roof, openings, airtightness and services, taken before they are concealed (Appendix B).

For new buildings other than dwellings, Volume 2 uses a target primary energy rate and target emission rate calculated through the National Calculation Methodology, plus minimum fabric and services standards.

The Future Homes and Buildings Standards

The Future Homes and Buildings Standards are the next uplift to Part L, designed so that new buildings will not need retrofitting to become zero carbon as the grid decarbonises. The regulations (SI 2026/335) and the new Approved Documents were published on 24 March 2026.

According to MHCLG Circular 01/2026, the regulations and the 2026 Approved Document L come into force on 24 March 2027 for work that is not higher-risk building work, and on 24 September 2027 for higher-risk building work and work to existing higher-risk buildings.

How the transitional arrangements work

For non-higher-risk work, the new standards do not apply to a building where a building notice, initial notice or full plans application was given before 24 March 2027, provided work on that building starts before 24 March 2028. Protection is building by building.

For higher-risk building work, the new standards do not apply where a valid building control approval application was submitted to the Building Safety Regulator before 24 September 2027 and has not been rejected. The 2026 regulations also revoke earlier transitional arrangements from 2013 and 2021 that let some sites keep building to older energy standards, subject to exceptions. On a long-running consented site, check which standard actually applies.

What changes in the 2026 Approved Document L

The 2026 edition is retitled "Approved Document L: Energy and greenhouse gas emissions", and Part L's aims are restated to cover reducing greenhouse gas emissions as well as conserving energy. The biggest practical changes are on-site renewables and low carbon heating.

The PV benchmark assumes panels facing south-east to south-west at a 45° pitch and not overshaded. GOV.UK published FAQs on requirement L3 in September 2026, including that north-facing or overshaded roof areas are not automatically excluded from the "reasonably practicable roof area". L3 applies subject to its limits on application.

The regulations do not name gas boilers, but the government's consultation response says they are unlikely to be present in new buildings given the guidance on the carbon intensity of heating fuel. In practice, new homes will use low carbon heating such as heat pumps or heat networks. For non-domestic buildings, the Future Buildings Standard requires low carbon heating and sets the notional building's PV at an area equivalent to 40% of the foundation area.

The fabric backstops have not moved. The step change comes from the notional dwelling, which sets the target.

SAP 10.3 or the Home Energy Model?

SAP 10.3 is the approved calculation method for dwellings when the new standard launches. The Home Energy Model (HEM), which will eventually replace SAP, was delayed and will not launch alongside the Future Homes Standard. Once HEM is approved, there will be a dual running period of at least 24 months in which either HEM or SAP 10.3 can be used.

What this means for projects in design now

Any scheme that will not start on site well before March 2028 should be tested against the 2026 edition now. Roof form, plant space and ventilation are much harder to change after stage 4.

• ✓
  Submission dates are checked. For non-higher-risk work, a full plans application or initial notice before 24 March 2027, and a start on each building before 24 March 2028, keeps the 2021 standard. Anything later is assessed against the 2026 edition.
• ✓
  Roofs are designed for PV. Requirement L3 affects roof form, plant space, orientation and parapet details. Retrofitting PV into a design after stage 4 is costly.
• ✓
  Heat pumps are planned. External unit locations, cylinder space and acoustics are resolved early, particularly in flats.
• ✓
  Approved Document F is coordinated. The 2026 changes include a revised Approved Document F Volume 1 for dwellings, so the ventilation strategy is checked against the edition that applies.
• ✓
  Long-running sites are rechecked. Older 2013 and 2021 transitional protections are revoked, subject to exceptions.

For how these requirements carry through into clauses, see our post on energy performance specifications from Part L to the Future Homes Standard.

Where Avoice fits

With two editions of Approved Document L live on GOV.UK, it is easy to cite the wrong one. Most errors come from quoting the 2021 guidance on a project that will be built to 2026, or the reverse.

Avoice Regulations lets teams read and search the full Approved Document L, both the 2021 and 2026 editions, alongside the Building Regulations 2010, with answers that cite whether they come from legislation or statutory guidance. In Avoice Practice, the Building Regs Tracker records which Part L edition applies to each project and the transition dates it relies on, and spec writing keeps U-value, PV and heat pump clauses consistent with the energy strategy.

Software can retrieve, compare and flag. The energy assessor, the architect and building control still decide which standard applies and whether the design meets it.