What evidence will building control expect for a liquid-applied roof system?

Building control tends to look for evidence that the system as installed, not just the individual products, does the job. In practice that usually means third-party approval or certification for the build-up, for example an accredited product certificate covering waterproofing performance and expected service life, reaction-to-fire evidence appropriate to the roof, and confirmation that UKCA or CE marking is in place where the products fall under a harmonised standard. Manufacturer's installation guidance, a system guarantee and evidence that the applicator is approved usually help too. The important point is that these apply to a defined system build-up, so mixing products across suppliers can quietly break the certification. Ask the system manufacturer for the certificate and its scope early, and if anything is missing or unclear for your specific detail, get in touch so it can be checked before you submit.