Part L Building Regulations Guide 2026: Energy Standards | ATSPACE

 

DOWNLOAD - Essential guide: New regulations U-value handbook: The latest updates to Part L Building Regulations:Approved Document L Energy Standards Specification

Building Regulations Part L addresses the conservation of fuel and power in new and existing homes in England. With buildings contributing about 40% of UK greenhouse gases, improving energy performance under Part L building regulations directly determines whether your scheme passes Building Control or halts completion.

Statutory Fabric Standards & Part L Framework

In June 2022, significant updates were made to Part L regulations to support the government’s net-zero target. The new rules emphasise a fabric-first approach and renewable technologies like heat pumps, aiming to reduce the carbon output of new homes by 31%. Standards for extensions and replacements in existing homes have also tightened.

To be exempt from these new requirements, projects adhering to the 2013 version of Approved Document L2A must have started on-site by 15 June 2023. These changes set the stage for the Future Homes Standard (FHS), which, starting in 2025, will require new homes to produce 75-80% fewer carbon emissions than those built to the previous standard. Transitional rules have now completely lapsed; all active plots must achieve full compliance under SAP 10.2 modelling without grandfathered exceptions.


Consolidation of Part L Documents

The updated Part L now consolidates into two documents:
- Approved Document L1 (ADL1): For new and existing domestic buildings
- Approved Document L2 (ADL2): For new and existing non-domestic buildings

These changes emphasise the importance of both fabric performance and low-carbon technologies in achieving energy-efficient homes. This structure merges new-build and renovation rules into single volumes, simplifying requirements across domestic and non-domestic developments.


Energy Performance Standards
The new standards, effective from 15 June 2022, set out detailed requirements for elements like floors, walls, and roofs, with a focus on improved insulation and reduced U-values. These standards are a precursor to the even stricter requirements anticipated under the Future Homes Standard in 2025. In practice, building to backstop limits will result in an immediate SAP failure. Compliance requires matching the SAP Notional Dwelling Recipe specifications.

Part L building regulations performance benchmarks compare against previous standards as follows:
- External Walls: 2013 Limiting = 0.30 W/m²K | Current Limiting Backstop = 0.26 W/m²K | SAP Notional Target = 0.18 W/m²K
- Ground Floors: 2013 Limiting = 0.25 W/m²K | Current Limiting Backstop = 0.18 W/m²K | SAP Notional Target = 0.13 W/m²K
- Pitched Roofs (Insulated at Ceiling): 2013 Limiting = 0.20 W/m²K | Current Limiting Backstop = 0.16 W/m²K | SAP Notional Target = 0.11 W/m²K
- Flat Roofs: 2013 Limiting = 0.20 W/m²K | Current Limiting Backstop = 0.16 W/m²K | SAP Notional Target = 0.11 W/m²K
- Windows and Rooflights: 2013 Limiting = 2.00 W/m²K | Current Limiting Backstop = 1.60 W/m²K | SAP Notional Target = 1.20 W/m²K
- External Doors: 2013 Limiting = 2.00 W/m²K | Current Limiting Backstop = 1.60 W/m²K | SAP Notional Target = 1.00 W/m²K
- Airtightness: 2013 Limiting = 10.0 m³/(h·m²) | Current Limiting Backstop = 8.0 m³/(h·m²) | SAP Notional Target = 5.0 m³/(h·m²)

Thermal bridging (psi values) now accounts for up to 30% of total heat loss. Default junction values penalise calculations heavily, making accredited or calculated junction details essential on site.

For detailed energy performance standards, refer to the downloadable Part L regulations sheet HERE!

On-Site BREL Compliance & Photographic Evidence

Sign-off under Part L building regulations requires indisputable photographic proof via the Building Regulations England Part L (BREL) report. Building Control Bodies will reject compliance reports if site teams fail to capture geo-located, high-resolution photos prior to plasterboard dry lining. Critical inspection stages include:
- Perimeter edge insulation at ground-bearing and beam-and-block floors.
- Continuous insulation fill around external cavity closures, lintels, and window reveals.
- Roof insulation continuity over wall plates, eaves, and loft hatches.
- Pipework, ductwork, and soil stack penetrations sealed before boxing in.

Missing photographic evidence forces destructive opening-up works or costly recalculations with punitive default penalties.

Interim Changes in Wales and Scotland

Devolved nations enforce distinct rules from English Part L building regulations, meaning regional specifications cannot be transferred without adjustment.

Wales: New amendments now require newly constructed buildings to follow the SAP 10 methodology and meet a minimum energy efficiency standard, aiming for an EPC rating of B or 81. Mandatory air-tightness testing is also required for new-build homes with all plots tested rather than sample testing.

Scotland: Revised Section 6 energy standards apply to new building applications received after 1 February 2023. These updates aim to reduce carbon emissions by 32% compared to the 2015 standards and include mandatory airtightness testing and measures to address overheating risks under Scottish Building Standards Section 6 and Section 3.

Commercial Action Plan for Site Managers & Developers

Treat airtightness and thermal detailing as structural disciplines, not a mastic panic on testing day. Air seals must be formed at plasterboard junctions, dry lining perimeters, service penetrations, and loft hatches during first fix. When soil stacks and dry water traps are unsealed, air test results fail immediately.

Securing first-time sign-off under Part L building regulations protects your construction schedule and stops costly remedial works. ATSPACE brings over 15 years of industry experience (est. 2008), supporting 12,000+ clients across England and Wales with 1,000+ 5-star reviews. From same-day quotes (8am–4pm Mon–Fri) to next-day compliance certification and dedicated account management, we steer your scheme through Building Control smoothly.

Need immediate compliance guidance or design-stage SAP modelling? Call our technical team directly on 0345 6465 454.

For more detailed information and to download the complete regulations here!