As-built Part L: the evidence pack building control expects

What the pack contains

Approved Document L sets the expectation clearly enough: at completion you need the as-built calculation, air tightness test results, commissioning records and photographic evidence of key construction details. Your building control body may want it presented in a particular order or through a particular portal, but the substance is the same everywhere, and it is all evidence about the building as it actually exists.

Photographic evidence: the part that cannot be redone

Every other item in the pack can, at a push, be produced late. Photographs of a junction that has been plastered over cannot. The plots that go through cleanly are the ones where site has a standing instruction to photograph the named details as each one is completed, with the plot number and date captured, and where someone reviews a sample early in the programme rather than at the end of it. The first plot of each house type is worth checking in detail — the habits set there tend to repeat across the site.

Air tightness testing

The air tightness result feeds directly into the as-built calculation, so it is one of the few pieces of site evidence that can turn a comfortable design-stage pass into an as-built problem. Two things reduce that risk: setting a design target the build can actually achieve rather than the best figure that makes the model work, and testing early enough in the programme that a detailing issue can be corrected on the remaining plots. We do not carry out air tightness testing ourselves; we tell you what the model needs and work with the results your tester provides.

Commissioning and controls

Commissioning records for the fixed building services are part of the compliance evidence, not an afterthought for the O&M manual. Under the 2026 edition of Approved Document L there is new and updated guidance on the commissioning and certification of fixed building services, on minimum services efficiencies and heat pump controls, and on limiting heat loss from low-carbon heating systems — all of which makes the quality of that paperwork more visible, not less.

Handling substitutions without a late failure

The realistic cause of as-built trouble is not fraud or incompetence; it is procurement. A window with a slightly different U-value, an alternative insulation board, a different heat pump model, a ventilation unit with a different specific fan power. Each is defensible on its own and each moves the calculation. A one-line email to your assessor at the point of substitution costs nothing and prevents the version of this conversation that happens with a buyer waiting to complete.

Who owns it

On the sites that run well, one named person owns the Part L evidence for each plot and knows what is outstanding at any point. It does not have to be a full-time role, and it does not have to be us — but where nobody owns it, the pack is assembled under pressure at hand-over, and that is exactly when a missing photograph becomes a delayed completion.