This is a ‘standing seam’ zinc roof. This build-up probably looks fine, right? It’s not — the design does not satisfy Requirement C2 in The Building Regulations 2010. There is no 50mm vented air gap at the eaves and no VCL on the ‘warm’ side of the insulation (ref: BS5250:2011+A1:2016). The condensation risk assessment results in a ‘fail’ (ref: BS EN ISO 13788:2012). The BBA certificate isn’t valid either and the build-up falls short of the manufacturer’s requirements.