C.2. Development is permitted by Class C subject to the following conditions—
(a)the appearance of the materials used in each element of any exterior work must so far as practicable match the appearance of the materials used in the equivalent element of the existing dwellinghouse; and
(b)if any element of a window inserted on a roof slope or other element of a side elevation of the dwellinghouse would, if projected downwards in a vertical line to ground level, be within 10.5 metres of any boundary of the curtilage of the dwellinghouse opposite the relevant side elevation, the window must be—
(i)obscure-glazed;
(ii)non-opening unless any part of the window which can be opened is, when measured at any point along the lowest edge of that part, at least 1.7 metres above the internal floor or stair of the dwellinghouse directly below that point; and
(iii)permanently maintained in compliance with paragraphs C.2(b)(i) and (ii).