Part L compliance for developers from £150 per plot

Part L 2021 tightened the standard significantly: dwellings must now demonstrate lower carbon emissions and primary energy use than the previous edition allowed, with fabric and ventilation standards to match, and non-domestic buildings face an equivalent tightening. Compliance is not a single certificate but a chain of evidence: a design-stage calculation showing the specification passes, a build that matches that specification, air tightness testing and ventilation commissioning results, and an as-built calculation confirming what was constructed still complies. Building control will not sign off without the as-built set, and no dwelling can be legally sold or let without its on-construction EPC.

The cheapest time to solve a Part L problem is before anything is built. We take drawings, elevations, construction build-ups and the proposed heating and ventilation strategy, and model each dwelling type or the whole non-domestic building against the target. Where a plot fails, we model the routes back to compliance and price them in terms of buildability rather than handing over a bare fail: better glazing versus better walls, a change of heat source, more airtight detailing, adding photovoltaics. Getting that decision right at design stage regularly saves more than the fee across a site.

Once the scheme is built, the calculations are re-run against what was actually installed — the boiler or heat pump that turned up, the glazing that was substituted, the insulation depths achieved — together with the measured air tightness results and the commissioned ventilation flow rates. That produces the as-built compliance evidence and the on-construction EPCs. Where substitutions have eroded the margin, we identify it and set out what recovers compliance, rather than discovering it at the point building control refuse to sign the building off.

Two things sink more Part L submissions than anything else: an air test result worse than the figure assumed in the design calculation, and ventilation that was never properly commissioned. Both are avoidable with sequencing. We advise on the air tightness figure to design to, coordinate the testing, and make sure ventilation commissioning records exist in the form the calculation and building control both need. Where a test comes back poor, we model what result is now required to keep the plot compliant and what specification change would achieve it.

Mixed schemes need both methodologies, and the interface between them is where things get missed — a residential block over commercial units, a converted building with new dwellings and retained non-domestic space, student accommodation with amenity floors. Running the SAP and SBEM work through the same consultant keeps the assumptions consistent, keeps the on-construction EPCs aligned with the compliance evidence, and gives you one person to call when building control raises a query rather than two firms pointing at each other.