Modelling and Compliance Checks

Compliance modelling answers a different question from advisory modelling. An advisory model asks which option looks best; a compliance model asks whether a building meets a defined standard, calculated in a defined way. That distinction governs everything else: the method is prescribed, the inputs must follow the method's rules, the software is usually approved for that method, and the result is judged against a threshold rather than against other options.

Because the method is prescribed, a compliance modeller has less freedom than an advisory modeller. Defaults, conventions and calculation rules are set by the standard, and departing from them to obtain a pass invalidates the result, even if the departure seems physically reasonable. Where a building feature is not covered by the method, the modeller should follow the method's treatment of uncovered features and record it, rather than inventing a treatment that helps the result.

Evidence is central to compliance. A compliance submission typically includes the calculation, the input schedule, product specifications for key items, and, for new builds, as-built evidence and commissioning records. The checker, whether a building control body, an accreditation scheme or another verifier, reviews whether the inputs are supported and the method correctly applied. A calculation without supporting evidence is an assertion, not a compliance demonstration, and it should be treated as incomplete.

Verification may also involve site checks, such as airtightness testing or inspection of insulation and details, depending on the regime. Those checks exist because a model describes an intended or recorded building, while compliance concerns the building as built. A model that passes on paper but fails on site has not demonstrated compliance in the sense that matters.

Before commissioning a compliance model, identify the exact requirement: which regulation, which version, which building type and which threshold. Ask the modeller to confirm that the method, software version and input conventions match that requirement, and to list the evidence they will need from you or from the construction team. If any of those items is uncertain, resolve it before modelling, because a model built to the wrong requirement is wasted work.

Also clarify who will check the submission and what form it must take. Some regimes require submission through a particular portal or scheme, some require a registered assessor or approved modeller, and some require specific supporting documents. Meeting the format and accreditation requirements is part of compliance, not an administrative afterthought.

Compliance routes differ markedly by place. In the UK, building regulations set energy requirements for new homes and some existing-home work, with SAP-based calculations and EPCs forming part of the system, while Scotland, Wales and Northern Ireland operate their own regimes. In EU member states, EPBD implementation sets minimum energy performance requirements through national building codes, with national calculation methods and certification systems. A compliance approach that works in one jurisdiction cannot be assumed to work in another.

Timing also matters. Regulations change, methods are revised and thresholds tighten, and a model prepared under an old version may not satisfy a new requirement. Check the version in force at the relevant date, which may be the date of application, construction or completion depending on the regime, and record which version the model used.

A common mistake is to commission an advisory model and present it as a compliance model. The two may look similar, but an advisory model that uses household-specific patterns or unapproved software does not demonstrate compliance, however careful it is. Another mistake is to treat a pass as a guarantee of real performance: compliance shows that a standardised calculation meets a threshold, not that the finished home will use a particular amount of energy in real use.

A further mistake is to leave evidence gathering until the end. Product specifications, photographs and commissioning records are easiest to collect during construction or survey, and reconstructing them afterwards is slower and less reliable. Build evidence collection into the project plan from the start.

Keep the regulation reference, the method and software version, the input schedule and all supporting evidence together as the compliance file. When a checker queries the submission, that file lets you answer from records rather than from memory.

Questions to ask include: which exact requirement must this model satisfy, is the method and software approved for that requirement, and what evidence will the checker expect. Clear answers to those questions prevent most compliance modelling failures.