Part L of the Building Regulations has been firmly in force since June 2023, yet compliance failures continue to dog housebuilders and main contractors across England. Projects stall at completion. Costly rework eats into margins. Completion certificates get withheld. And with the Future Homes and Buildings Standard on the horizon, the stakes are only going to rise.
So why are so many sites still getting it wrong — and what does a proactive compliance process actually look like?
The Regulatory Landscape: Where We Are Now
The 2021 update to Approved Document L introduced the biggest shake-up to energy efficiency requirements in a generation. New dwellings must now achieve a 31% reduction in CO₂ emissions compared to 2013 standards, assessed under the updated SAP 10.2 methodology. U-values tightened. Air permeability targets dropped from 10 to a maximum of 8 m³/(h·m²)@50Pa. And critically, every single dwelling — not a sample — now requires a pressure test.
Alongside performance targets, the 2021 update introduced two new mandatory documents: the design-stage BREL report and the as-built BREL report. Both must be signed by the developer and energy assessor, and both must be backed by photographic evidence of key construction stages. Without them, building control cannot issue a completion certificate — meaning the property cannot be sold or legally occupied.
This is a compliance regime that demands far more from sites than a box-tick at handover. Yet for many housebuilders, the response has been reactive rather than systematic.
Why Failures Are Still Happening
1. The BREL Photo Burden Is Being Underestimated
Photographic evidence is mandatory across six stages of construction: foundations, external walls, roof structure, openings (windows and doors), airtightness details, and building services. Each image must be unique to the individual plot — the same photo cannot be reused across identical units, even on the same development. Images need to be high resolution, geo-tagged with location, date and time, and clearly labelled to the specific plot and detail.
In practice, this is a significant operational demand on site teams already managing tight programmes. According to research by Housebuilder & Developer magazine, 71% of housebuilders report experiencing BREL photo reporting issues, with 21% describing it as their biggest compliance challenge. Photos taken informally on personal phones get lost in crowded camera rolls. Labelling is inconsistent or absent. By the time a SAP assessor reviews the submission, gaps are identified — often when it’s too late to capture the evidence without intrusive inspection or remedial works.
2. Thermal Bridging Is Being Left to Chance
Thermal bridging has always mattered, but Part L 2021 makes it non-negotiable. Without properly calculated psi-values (Ψ-values) for all key junctions, a default y-value of 0.20 W/m²K is applied in the SAP calculation — a figure so penalising that most dwellings will fail to meet the Target Fabric Energy Efficiency (TFEE) if it’s used.
Yet thermal bridging details are frequently treated as a late-stage consideration rather than a design input. Approved junctions are specified, then quietly substituted on site. Drawings aren’t updated. The SAP calculation isn’t revised. By the time building control scrutinises the as-built BREL report, the discrepancy between design intent and built reality undermines the entire assessment. It’s estimated that thermal bridges can account for 20–30% of heat loss in new-build homes — a compliance risk and a performance gap that directly affects homeowner energy bills.
3. The Design-to-Site Gap Remains Unresolved
The BREL report exists specifically to close the gap between what was designed and what was built. But closing that gap requires an active audit trail throughout the build — not a retrospective scramble at completion. When product substitutions happen without being logged and fed back into the SAP calculation, the as-built report can no longer accurately reflect the dwelling. When insulation is installed behind closed cavities before being photographed, there’s no way to verify compliance. When site managers change and knowledge walks out the door, continuity of evidence breaks down.
The performance gap between design-stage energy modelling and real-world building performance is a well-documented industry problem. The BREL regime was designed to address it — but it only works if compliance is treated as a live process, not an end-of-project administration task.
4. Knowledge Gaps Remain Surprisingly Common
Despite the regulations having been in force for over two years, a 2025 survey by Polypipe Building Products found that only 27% of housebuilders have comprehensive knowledge of Part L, and fewer than a third felt confident they were fully up to date with its requirements. With Part L, Part O, Part F, and the Building Safety Act all overlapping — and ADL 2025 still creating planning uncertainty — it’s no surprise that some teams are operating with incomplete understanding of their obligations.
What Prevention Actually Looks Like
Getting Part L right is not about adding more administration. It’s about integrating compliance into how the build is run from day one.
Start with thermal bridging in design, not on site. Commission bespoke psi-value calculations for all key junctions at specification stage. Ensure any product substitutions during construction are immediately flagged and fed back to the SAP assessor for recalculation.
Treat photographic evidence as a site activity, not a paperwork exercise. Assign clear responsibility for capturing photos at each of the six stages. Use a structured digital process — rather than unmanaged phone cameras — to ensure images are geo-tagged, labelled, and linked to the correct plot and detail in real time.
Close the design-to-site loop with a live audit trail. Every change from the design-stage BREL — materials, U-values, service specifications — needs to be captured, communicated, and documented. Building control are looking for evidence that the dwelling was built as designed. If it wasn’t, they need to see that changes were properly managed and recalculated.
Get air pressure testing right, first time. With sample testing no longer permitted, every dwelling is exposed. Identify high-risk details early — penetrations, junctions, service entries — and inspect them before they’re concealed. Failures after closing up a wall are expensive to diagnose and costly to fix.
Build in a pre-completion check. Before the SAP assessor submits the as-built BREL report, run an internal review of photo coverage, product substitution logs, and pressure test results. Identify gaps while remediation is still straightforward.
The Stakes Are Rising
Part L 2021 is not the finish line. The Future Homes and Buildings Standard — expected to come into effect in late 2026 — will demand homes produce 75–80% fewer carbon emissions than current standards. The compliance documentation regime will become more demanding, not less. Housebuilders who treat the current BREL framework as a burden to be managed reactively are already in the wrong posture for what’s coming.
The firms that are getting this right are those treating compliance as a live operational discipline — where evidence is captured in real time, changes are tracked rigorously, and every plot has a clear, auditable record before completion is requested.
How PlanRadar Supports Part L Compliance
PlanRadar’s construction management platform helps housebuilders and main contractors build the audit trail that Part L demands. From site-level photo capture linked directly to plot and build stage, to defect tracking that flags issues before elements are concealed, to real-time document management that keeps design intent and as-built records aligned — PlanRadar gives site teams and compliance managers the visibility they need at every stage of the build.
As Rob Norton, UK Director at PlanRadar, has noted: without proper quality control measures, housebuilders risk Part L failures that result in expensive rework eating into already tight margins.
If your team is navigating BREL reporting, airtightness sign-off, or the wider compliance demands of Part L, talk to PlanRadar about how our platform can help you stay ahead.
