As-Built BRUKL Report

The as-built BRUKL report is the second and final compliance submission required for every new non-domestic building under Part L. It must be provided to the building control body after construction, confirming that the building as actually constructed meets both the Target Primary Energy Rate (TPER) and Target Emission Rate (TER). Without a satisfactory as-built BRUKL, the completion certificate cannot be issued (AD L2 2026, Appendix C).

What does the as-built BRUKL require?

The as-built BRUKL report is produced using SBEM or an approved Dynamic Simulation Model, just like the design stage version. However, it must reflect the building as actually constructed, not the design intent. The report must include (AD L2 2026, Appendix C):

• As-built BPER and TPER — the Building Primary Energy Rate calculated from as-built specifications, demonstrated to be no greater than the target
• As-built BER and TER — the Building Emission Rate confirmed as meeting the target
• As-built fabric specifications — actual U-values, including any changes from the design stage
• Measured air permeability from pressure testing (replacing the design stage target with the actual test result)
• Final HVAC system specifications as installed and commissioned
• As-installed lighting specification and efficacy
• As-installed renewable energy systems, including actual PV capacity
• Any changes from the design stage BRUKL and supporting specifications

Air permeability testing

One of the most significant differences between the design stage and as-built BRUKL is the air permeability value. At design stage, the assessor uses a design target. At the as-built stage, this is replaced by the measured result from a pressure test (AD L2 2026, Regulation 43).

Key requirements for pressure testing:

• All non-domestic buildings must be pressure tested, including extensions treated as new buildings. Testing follows CIBSE TM23 Testing Buildings for Air Leakage
• The only exemption is buildings with less than 500 m² total useful floor area — but these must use a default air permeability of 15 m³/(h·m²) at 50 Pa in the calculation, which is deliberately punitive
• The BPER and BER calculated using the measured air permeability must not exceed the target rates. If they do, the building fails compliance
• Results of all pressure tests — including failures — must be reported to the building control body
• Testing equipment must be calibrated at least every 24 months by a UKAS-accredited facility

What changes between design and as-built?

It is common for the as-built BRUKL to differ from the design stage submission. Changes typically fall into three categories:

• Air permeability — the design target is replaced by the measured pressure test result. This is the single most frequent change and can shift the compliance outcome in either direction
• Specification substitutions — products substituted during construction (different window manufacturer, different heat pump model, different insulation thickness). Each substitution must be reflected in the as-built calculation with accurate performance data
• Design amendments — changes to the building geometry, services layout or renewable energy provision made during construction. These may have been captured in revised design stage submissions, but must all be reflected in the final as-built report

The assessor must verify that the as-built specifications match what was actually installed. This typically requires site information from the contractor, including product data sheets, commissioning records and the pressure test certificate.

Commissioning records

The as-built BRUKL sits alongside the commissioning process required under Regulations 44 and 44ZA (AD L2 2026, Section 7). All fixed building services must be commissioned to ensure they use no more fuel and power than is reasonable. On-site electricity generation systems must be commissioned to ensure they produce as much electricity as is reasonable.

Commissioning includes:

• Setting to work, regulation (testing and adjusting to achieve specified performance), and calibration of all fixed building services
• Setting up and testing associated automatic control systems
• Recording system settings and performance test results
• A notice of completion must be given to building control within 5 days of commissioning completion for full plans applications (AD L2 2026, para 7.7)

The completed commissioning records form part of the building log book that must be provided to the building owner within 5 days of work completion (AD L2 2026, Section 8). The assessor may need commissioning data to finalise the as-built BRUKL — particularly for HVAC system performance and control settings.

Relationship to the EPC

The as-built BRUKL and the Energy Performance Certificate (EPC) for a new non-domestic building are closely related but serve different purposes:

• The BRUKL demonstrates Part L regulatory compliance — it compares the building's energy performance against the targets derived from the notional building
• The EPC rates the building's energy efficiency on an A–G scale for the purposes of sale, letting and construction — it uses the same SBEM calculation data but presents it differently

In practice, the as-built BRUKL data feeds directly into the ‘on-construction’ EPC. Both are typically produced by the same qualified Non-Domestic Energy Assessor at the same time. The EPC cannot be lodged until the as-built calculation is complete, and the EPC is itself required before the completion certificate is issued.

Completion certificate dependency

The as-built BRUKL is one of several documents that building control requires before issuing the completion certificate. The full chain of dependencies is:

1. Construction is completed and all fixed building services are installed
2. Air permeability pressure testing is carried out and the results reported to building control
3. All fixed building services and on-site generation systems are commissioned, with the notice of completion given to building control within 5 days
4. The energy assessor produces the as-built BRUKL using measured air permeability, final specifications and commissioning data
5. Both the assessor and client sign the as-built BRUKL
6. The on-construction EPC is produced and lodged on the national register
7. The building log book, including commissioning records, is provided to the building owner
8. Building control issues the completion certificate

Common issues and how to avoid them

As-built BRUKL submissions frequently encounter problems that delay the completion certificate. The most common issues are:

• Pressure test failure — the measured air permeability is worse than the design target, causing the as-built BER or BPER to exceed the target. Remedial airtightness work and retesting may be needed
• Undocumented substitutions — products were changed during construction without informing the assessor. The as-built BRUKL must reflect what was actually installed, and discovering substitutions late in the process causes delays
• Missing commissioning data — the assessor cannot finalise the as-built BRUKL without commissioning records for HVAC systems. Late commissioning or incomplete records hold up the entire process
• Specification downgrade — a value-engineered change during construction (e.g. thinner insulation, lower-rated heat pump, reduced PV capacity) tips the building below the compliance threshold. The assessor should be consulted before any specification changes are agreed
• Incorrect building geometry — the as-built floor areas or zone definitions differ from the design stage model. Significant geometry changes require the assessor to rebuild parts of the SBEM model
• Late assessor engagement — appointing the energy assessor only at the completion stage means they have no design stage context. This increases both the time and cost of producing the as-built report

The simplest way to avoid these issues is to maintain communication between the contractor, design team and energy assessor throughout the construction phase. A change log tracking any specification changes, combined with early scheduling of pressure testing and commissioning, keeps the as-built BRUKL on the critical path rather than a last-minute bottleneck.

As-built compliance under the FBS

Under the Future Buildings Standard, the tightened targets leave less margin between design and as-built stages. Small specification downgrades or a worse-than-expected pressure test result can push a building from compliant to non-compliant. This makes:

• Accurate design stage modelling more important — realistic inputs at design stage reduce the risk of surprises at as-built
• Construction quality critical — the notional building assumes 3 m³/(h·m²) air permeability for side-lit zones (5 for top-lit), and careful airtightness detailing remains essential for meeting overall compliance targets
• Substitution control essential — any product substitution should be checked against the energy model before being approved

Need an as-built BRUKL?

If you need BRUKL calculations for your non-domestic project, visit Easy EPC for professional SBEM assessment and compliance support from qualified Non-Domestic Energy Assessors.