Can anyone answer if replacement windows, are an engineering operation and thus development. The next question is whether they are permitted by the GPDO. In the case of dwellinghouses Class A the section on windows states: A.3 Development is permitted by Class A subject to the following conditions— (a) the materials used in any exterior work (other than materials used in the construction of a conservatory) shall be of a similar appearance to those used in the construction of the exterior of the existing dwellinghouse; (b) any upper-floor window located in a wall or roof slope forming a side elevation of the dwellinghouse shall be— (i) obscure-glazed, and (ii) non-opening unless the parts of the window which can be opened are more than 1.7 metres above the floor of the room in which the window is installed; and (c) where the enlarged part of the dwellinghouse has more than one storey, the roof pitch of the enlarged part shall, so far as practicable, be the same as the roof pitch of the original dwellinghouse. The word development at the beginning of the section suggests they are 'development' which is permitted in particular circumstances. This section doesn't differentiate between replacement windows or windows in new openings because it uses the word 'any'. Therefore although this may have not been the writers intention, it appears both must follow the same criteria, and therefore any upper floor window, whether a replacement or a new one in a new opening must meet criteria (i) and (ii) in order to benefit from the rights under Class A
