Quick Answer
Part L 2021 (England) came into force on 15 June 2022. New dwellings must produce at least 30% less CO2 than under the 2013 edition. Key changes include tighter U-values (walls now 0.26 W/m²K, roofs 0.16 W/m²K), mandatory air pressure testing on every new home, a 55°C maximum heating flow temperature, new SAP 10 calculations, and a legal requirement for photographic evidence at each stage. Every trade on a new build is affected. Read on for the breakdown by trade and how to price it correctly.
Table of Contents
What is Part L and who does it apply to?
Part L of the Building Regulations covers the conservation of fuel and power in buildings. It sets minimum energy performance standards for new buildings, extensions, and certain alterations. There are two volumes: Volume 1 covers new dwellings (houses and flats), Volume 2 covers buildings other than dwellings (offices, shops, industrial units).
In practice, Part L affects almost every trade on a new build or significant renovation. If you are laying foundations, fitting windows, installing heating, or adding roof insulation, Part L applies. It is enforced by Local Authority Building Control (LABC) or an approved inspector, and non-compliance can result in a building notice being rejected or costly remedial works after completion.
Who enforces Part L?
Building Control Officers (BCOs) from the local authority or an approved inspector check compliance at each stage. From 2022, inspections are more rigorous, and photographic evidence is now a legal requirement. Failing an air pressure test after completion can mean costly remedial work and delays to handover.
The seven key changes from June 2022
Part L 2021 (published December 2021, effective 15 June 2022) replaced the 2013 edition. Here are the seven changes that matter most to tradespeople.
1. Tighter U-values across the board
The target U-values for new dwellings dropped significantly. These are the values your building element must hit to pass Building Control:
| Building Element | Pre-2022 (Target) | Post-2022 (Target) |
|---|---|---|
| External walls | 0.30 W/m²K | 0.26 W/m²K |
| Ground floors | 0.25 W/m²K | 0.18 W/m²K |
| Roofs | 0.20 W/m²K | 0.16 W/m²K |
| Windows (target) | 1.40 W/m²K | 1.20 W/m²K |
| Windows (limiting) | 2.00 W/m²K | 1.60 W/m²K |
To achieve the tighter wall U-value of 0.26 W/m²K with a standard brick/block cavity wall, you typically need 125-150mm of mineral wool or PIR insulation in the cavity. Floor insulation depths for ground-bearing slabs have also increased substantially to hit 0.18 W/m²K.
2. Mandatory airtightness testing on every home
Previously, developers could test a sample of homes on large plots rather than testing every single one. That sampling exemption is gone. Under Part L 2022, every new dwelling must be air pressure tested by an accredited tester. The target is ≤5 m³/(h.m²) at 50 Pa, with a maximum permitted value of 8 m³/(h.m²).
This is done using a blower door test, where a large fan temporarily replaces the front door and depressurises the building to 50 Pa. Any air leaks show up as pressure failure. Testing must be carried out by an accredited organisation (e.g. ATTMA registered) and the result fed into the SAP calculation.
3. Maximum heating flow temperature of 55°C
New heating systems in new dwellings must be designed and set to operate at a maximum flow temperature of 55°C. This was previously unregulated in Part L, with systems often set to 70-80°C. The lower flow temperature is designed to work with heat pumps (which run efficiently at 35-55°C) and to make future decarbonisation easier under the Future Homes Standard.
For gas boilers, this means the commissioning engineer must set the boiler flow temperature at or below 55°C using the boiler's built-in controls. The minimum gas boiler efficiency for new installations is now 92% (ErP A rating), and oil boilers must achieve 91%.
4. SAP 10 replaces SAP 2012
The Standard Assessment Procedure (SAP) is the government’s method for assessing the energy performance of dwellings. Part L 2022 requires SAP 10.1 (now 10.2) instead of SAP 2012. The most significant change in SAP 10 is the updated electricity carbon factor: it dropped from 0.519 to 0.136 kg CO²/kWh. This reflects the UK grid’s increasing proportion of renewables and massively favours electric heating (air source heat pumps, etc.) over gas in energy calculations.
5. Target Primary Energy Rate (TPER) metric
Part L 2022 introduces a new compliance metric alongside the CO² target: the Target Primary Energy Rate (TPER). This measures the total primary energy used by the dwelling per square metre, including the energy used to generate and distribute the fuel. A new build must meet BOTH the CO² target AND the TPER. This dual-metric approach was designed to prevent developers from gaming the system by switching to low-carbon fuels without genuinely reducing energy demand.
6. Bespoke Psi values for thermal bridging
Thermal bridges are places where heat leaks through the building fabric at junctions (e.g. where a wall meets the floor, or where a window frame sits in an opening). Under the old rules, developers could use default “Accredited Construction Details” (ACDs) for their linear thermal transmittance (ψ values). Under Part L 2022, bespoke Psi values are required for each junction type. This forces greater design care at critical junctions and typically requires the architect or engineer to calculate the ψ value for each detail used on the project.
This affects groundworkers and bricklayers directly
The thermal bridging details at wall-floor junctions, lintel positions, and sill-to-frame connections must now be built exactly as drawn. Deviations from the design details can invalidate the SAP calculation and fail the compliance report. If you substitute materials or change junction details on site, notify the SAP assessor immediately.
7. Photographic evidence at each stage
Part L 2022 introduces a formal requirement for photographic evidence throughout the build process. This includes photos of insulation installation before it is covered up, airtightness membrane installation, and window and door installation showing the thermal detail. These photos form part of the Building Regulation Inspection Report (BRIEL) and are submitted to Building Control as evidence of compliance. Keep a timestamped photo record on every job.
How different trades are affected
Builders and groundworkers
The biggest hit is on ground floor and wall insulation depths. To achieve 0.18 W/m²K on a ground-bearing concrete slab, you typically need 150mm of PIR foam (e.g. Celotex or Kingspan) or 200mm of EPS, depending on the ground configuration. Cavity walls now need 125-150mm of full-fill insulation rather than the 100mm that was common before 2022. This increases material costs and can affect door and window reveal widths, which knock on to the window installer’s design.
Bricklayers also need to be more careful at thermal bridge junctions. Wall ties must be the correct type (low-conductivity stainless), and the junction details at sills, lintels, and wall-floor interfaces must match the SAP design exactly. Take photos at each stage.
Heating engineers
The 55°C maximum flow temperature affects commissioning. When commissioning a gas boiler in a new build, the flow temperature must be set at or below 55°C using the boiler’s heating curve or programmer. Gas Safe recommends documenting this at commissioning with a photo of the settings. For heat pump installations, the system design should already be at 45-55°C flow, so this is less of a change.
The boiler efficiency minimum of 92% (ErP A rating) means basic boilers are out. This is the standard for most modern condensing boilers anyway, but check the ErP label before specifying on a new build.
Window installers and glazing contractors
The target window U-value for new dwellings dropped from 1.4 to 1.2 W/m²K, with a hard limit of 1.6 W/m²K. Triple glazing (typically 0.8-1.0 W/m²K) is now common on higher-specification new builds. The window-to-wall junction detail (Psi value) is also more critical. A poorly detailed reveal can add 10-20% to the building’s heat loss at junctions. Coordinate with the SAP assessor on window reveal details before ordering frames.
Roofers and insulation contractors
Roof insulation must now achieve 0.16 W/m²K. For a standard ventilated cold loft with mineral wool, this means a minimum of 400mm of glass wool (typically 100mm between joists plus 270mm cross-batten). For warm roof constructions or flat roofs, the required PIR thickness increases substantially to meet the target. Airtightness detailing at the eaves is also critical, as the roof-wall junction is a common thermal bridge and air leakage point.
Cost impact: how much more does Part L 2022 add?
On a typical 3-bedroom detached new build, the additional material cost from Part L 2022 versus the 2013 edition is approximately £1,500 to £3,000 in extra insulation, airtightness membranes, and testing fees. The airtightness test alone costs £250-500. A SAP assessment for a new dwelling costs £200-400. These costs must be reflected in your quotes, particularly for groundwork, plastering, and heating contracts where the additional labour and material is most significant.
How to adjust your quotes
Part L 2022 has specific, quantifiable cost impacts. Here is what to add to your quotes on new build projects.
Insulation materials
Check the SAP design document (ask the developer’s SAP assessor or architect) for the required U-value targets and the specified insulation product. Do not substitute without telling the assessor. Common increases versus pre-2022 specs:
- Ground floor insulation: Budget for 150mm PIR or 200mm EPS rather than 100mm. Add £15-25/m² to your groundwork quote depending on access and configuration.
- Cavity wall insulation: Full-fill 125-150mm mineral wool or PIR bead rather than 100mm partial fill. Extra cost is typically £3-8/m² of wall area.
- Roof insulation: 400mm total glass wool depth versus 270mm previously. Material cost increase is approximately £5-10/m².
- Window specification: Triple glazing or high-spec double with warm-edge spacers. Window cost uplift of £80-150 per window versus standard double glazing.
- Airtightness membranes: Breather membranes and vapour control layers to AVCL specification. Allow £500-1,000 for a 3-bed detached in additional membrane costs.
Testing and compliance costs
These are fixed costs that should be included in every new build quote or contract:
- Air pressure test (ATTMA): £250-500 per dwelling. Book in advance; retests cost the same again. Budget for one retest on tight airtightness specifications.
- SAP assessment (DEA): £200-400 per dwelling. Usually the developer’s cost, but worth confirming who is responsible in your contract.
- Photographic documentation time: Allow half a day per trade per dwelling for photographing and labelling compliance photos at each stage. This is a real cost that is often overlooked.
Protect yourself on specifications
If you are pricing from a tender package that references 2013 Part L specifications, flag it immediately. Many older tender documents have not been updated. Quote on the correct 2022 specification and note the discrepancy in writing. If you build to an under-specified design and fail the SAP or airtightness test, the remedial costs could fall on you.
Part L timeline: 2006 to the Future Homes Standard
Part L has been tightened in stages since 2006. Here is the progression, so you know where the current standard fits in the bigger picture.
Part L evolution at a glance
2006: Part L 2006 introduced the first significant energy efficiency requirements for new dwellings. Wall target U-value: 0.35 W/m²K. Airtightness testing on sample basis only.
2010: Part L 2010 tightened requirements by 25% versus 2006 standards. Wall target dropped to 0.30 W/m²K. SAP 2009 introduced.
2013: Part L 2013 made modest improvements. This edition remained in force for almost a decade.
15 June 2022: Part L 2021 (the current edition) came into force. 30% CO² reduction target, tighter U-values, mandatory airtightness testing on every home, SAP 10, 55°C flow temperature maximum.
December 2026 (planned): Future Homes Standard. New builds will need to produce 70-80% less CO² than a 2013-compliant home. Gas boilers are expected to be effectively banned in new builds from this date. Heat pumps, solar PV, and MVHR are likely to be standard specification.
Future Homes Standard: start preparing now
The Future Homes Standard (originally planned for 2025, now expected December 2026) will require far more radical changes than Part L 2022. Tradespeople who get comfortable with heat pump commissioning, mechanical ventilation, and Passivhaus-style airtightness detailing now will be ahead of the curve when it lands. Developers are already specifying to Future Homes Standard voluntarily on some schemes.
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What the trades community thinks
Frequently asked questions
Part L applies to new dwellings in full. For extensions and renovations, the rules are more nuanced. Extensions over a certain size must meet the new build fabric standards for the extension itself. Replacing a “thermal element” (e.g. re-rendering an external wall or replacing a flat roof) triggers a requirement to upgrade that element to a set standard. Replacing more than 50% of an existing window triggers compliance with the new limiting U-value of 1.6 W/m²K. Always check Approved Document L Volume 1 (or consult your BCO) if you are unsure whether a renovation job triggers Part L.
Yes. If a full plans application or building notice was submitted before 15 June 2022, the project could proceed under the 2013 Part L rules provided work started on site before 15 June 2023. If you have a project that was designed under the old rules but has not yet started on site, check the submission date against these deadlines. Anything submitted after 15 June 2022 must comply with the 2022 edition. Any project where work started after 15 June 2023 must comply regardless of when the application was submitted.
If a dwelling fails the air pressure test, you have three options: carry out remedial works to seal the air leaks and retest; use the failed test result in the SAP calculation (if the result is between 8 and 15 m³/h.m², the dwelling may still pass SAP if the fabric is good enough elsewhere); or fit whole-house mechanical ventilation with heat recovery (MVHR) to compensate, if this was not already in the design. In practice, a failed airtightness test means finding and sealing the leaks. Common culprits are penetrations through the airtightness layer (pipes, cables), service voids, letterboxes, and poorly taped membrane joints. The retest costs the same as the original test.
The 55°C maximum flow temperature applies to the heating system as installed and commissioned in a new dwelling. It is set during commissioning by the heating engineer. It does not retrospectively apply to existing properties. However, the Boiler Plus regulations (which apply to existing domestic gas boiler replacements) require time-weather compensation or a flue gas heat recovery device to be fitted. For new builds specifically, the 55°C maximum is a Part L compliance requirement that must be documented and submitted to Building Control as part of the commissioning record.
The Future Homes Standard (FHS) is the government’s next major update to Part L. It was originally planned for 2025 but is now expected in December 2026. The FHS requires new homes to produce 70-80% less CO² than a 2013-standard home, compared to the 30% required by Part L 2022. In practice, this is expected to mean: no fossil fuel heating systems in new builds (gas boilers effectively banned), air source heat pumps or electric heating as standard, photovoltaic solar panels on most new homes, high-performance triple glazing, very tight airtightness targets, and MVHR as standard specification. A Future Homes Standard interim uplift (FHS 2025 Transitional) applies from June 2025 onwards for planning applications, requiring a 31% improvement in dwelling emission rate over the current standard.
Yes. Every new dwelling requires a SAP assessment carried out by an accredited Domestic Energy Assessor (DEA). The SAP assessor produces a Predicted Energy Assessment (PEA) at the design stage (submitted with the building regulations application) and an Energy Performance Certificate (EPC) at completion. The SAP calculation feeds directly into the Part L compliance check. As a tradesperson, your job is to build to the specifications in the SAP design. If you substitute materials or change junction details, notify the SAP assessor, as any change can alter the compliance outcome.
Our Verdict
Part L 2022 is the biggest change to building energy regulations in a decade. The 30% CO² reduction target is real and enforceable, and the move to mandatory airtightness testing on every new home has shifted compliance from a box-ticking exercise to a genuine technical challenge. The seven changes covered in this guide each have direct cost and labour implications for every trade on a new build. The time to understand them is before you price the job, not after the BCO visit.
Most affected trades: Builders (groundwork, brickwork), heating engineers (flow temp commissioning), roofers (400mm insulation depth), window installers (1.2 W/m²K target)
Key cost to add to quotes: £250-500 for airtightness test, £200-400 for SAP assessment, £1,500-3,000 additional insulation materials on a 3-bed detached
What’s coming next: Future Homes Standard (December 2026) will be far more disruptive. Start upskilling on heat pumps, MVHR, and airtightness detailing now.
One rule to follow: Photograph everything, build to the SAP spec, and get the BCO on side early. Surprises at handover are expensive for everyone.
