C. Any other alteration to the roof of a dwellinghouse.
C.1. Development is not permitted by Class C if—
(a)the alteration would protrude more than 15 centimetres beyond the plane of the slope of the original roof when measured from the perpendicular with the external surface of the original roof;
(b)it would result in the highest part of the alteration being higher than the highest part of the original roof;
(c)it would consist of or include—
(i)the installation, alteration or replacement of a chimney;
(ii)the installation, alteration or replacement of a microwave antenna;
(iii)the installation, alteration or replacement of an air source heat pump, solar PV, solar thermal equipment or a flue forming part of a biomass heating system or combined heat and power system;
(iv)the construction or provision of a veranda or raised platform;
(v)the construction or provision of a balcony which—
(aa)contains a platform of any description;
(bb)projects from the part of the exterior of the dwellinghouse to which it is affixed by more than 30 centimetres; or
(cc)if projected downwards in a vertical line to ground level, is within 10.5 metres of any boundary of the curtilage of the dwellinghouse opposite the relevant side elevation;
(vi)the construction or provision of a roof terrace, whether or not it would incorporate associated railings, fencing or other means of enclosure;
(vii)the removal of a chimney from a dwellinghouse on article 1(5) land or within a World Heritage Site; or
(d)the alteration would consist of or include the insertion of a roof light into a roof slope and the dwellinghouse is on article 1(5) land or within a World Heritage Site.
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).
C.3. For the purposes of paragraph C.1(b)—
(a)in the determination of the height of the highest part of the original roof, no account is to be taken of any relevant structure projecting from that roof;
(b)in the determination of the height of the highest part of the alteration, account is to be taken of any relevant structure comprised in the alteration; and
(c)“relevant structure” means any parapet wall, firewall, chimney or other roof furniture or similar structure.