Under regulations, the guidelines for permitted development are undeniable: “Materials must exhibit a similar appearance to the existing house.” When submitting an application for review under the GPDO legislation, a case officer meticulously assesses all aspects, with a particular focus on materials. Failure to align the proposed materials with those currently present on the house, such as tiles or slate, will result in refusal based on non-compliance. Compliance with material consistency is a crucial determinant in the approval process.