Class B — additions to the roof of a dwellinghouse (loft conversions and dormers)

Class B – additions etc to the roof This provides permitted development rights for the enlargement of a house consisting of an addition or alteration to its roof. Under Class B the following limits and conditions apply: B.1 Development is not permitted by Class B if – a) permission to use the dwellinghouse as a dwellinghouse has been granted only by virtue of Class M, N, P, PA or Q of Part 3 of this Schedule (change of use) Enlargement is not permitted where the house was created under the permitted development rights to change use, set out in Classes M, N, P, PA, and Q of Part 3 of Schedule 2 to the Order (see page 4). (b) any part of the dwellinghouse would, as a result of the works, exceed the height of the highest part of the existing roof Additions and alterations made to a roof to enlarge a house (for example a loft conversion or the replacement of an existing flat roof with a pitched roof) will only be permitted development if no part of the house once enlarged exceeds the height of the highest part of the roof of the existing house. If it does, planning permission will be required. The highest part of the roof of the existing house will be the height of the ridge line of the main roof (even though there may be other ridge lines at a lower level) or the height of the highest roof where roofs on a building are flat. Chimneys, firewalls, parapet walls and other protrusions above the main roof ridge line should not be taken into account when considering the height of the highest part of the roof of the existing house. (c) any part of the dwellinghouse would, as a result of the works, extend beyond the plane of any existing roof slope which forms the principal elevation of the dwellinghouse and fronts a highway The effect of this is that dormer windows as part of a loft conversion, or any other enlargement of the roof space, are not permitted development on a principal elevation that fronts a highway and will therefore require an application for planning permission. Roof- lights in a loft conversion on a principal elevation may however be permitted development as long as they meet the requirements set out under Class C (see page 38). Principal elevation has the meaning set out in the ‘General Issues’ section of this document (see page 7). The principal elevation could include more than one roof slope facing in the same direction. For example, where there are large bay windows on the front elevation, or where there is an ‘L’ shaped frontage. In such cases, all such roof slopes will form the 34 principal elevation and the line for determining what constitutes ‘extends beyond the plane of any existing roof slope’ will follow these slopes (see guidance on Class A (e) for an illustration of this on page 15). The extent to which an elevation of a house fronts a highway will depend on factors such as those set out in relation to Class A (e) (see page 16). (d) the cubic content of the resulting roof space would exceed the cubic content of the original roof space by more than - (i) 40 cubic metres in the case of a terrace house, or (ii) 50 cubic metres in any other case For the purposes of Class B “resulting roof space” means the roof space as enlarged, taking into account any enlargement to the original roof space, whether permitted by this Class or not. To be permitted development any additional roof space created must not increase the volume of the original roof space of the house by more than 40 cubic metres for terraced houses and 50 cubic metres for semi-detached and detached houses. Any previous enlargement to the original roof space in any part of the house must be included in this volume allowance. ‘Terrace house’ has the meaning set out in the ‘General Issues’ section of this document (see page 6). ‘Original roof space’ will be that roof space in the ‘original building’ (see ‘General Issues’ on page 6 for the definition of this). (e) it would consist of or include - (i) the construction or provision of a verandah, balcony or raised platform, or (ii) the installation, alteration or replacement of a chimney, flue or soil and vent pipe Alterations to the roof of a house for loft conversions involving the creation of balconies are not permitted development and will require planning permission. ‘Balcony’ can be understood as set out on page 29. Installation, alteration or replacement of chimneys, flues or soil and vent pipes will often be necessary when loft conversions are undertaken. Whilst these are not permitted development under Class B of Schedule 2 to the Order, they may be permitted development under Class G. (f) the dwellinghouse is on article 2(3) land In National Parks, the Broads, areas of outstanding natural beauty, conservation areas, and land within World Heritage Sites, roof extensions are not permitted development and will require an application for planning permission. 35 Conditions B.2 Development is permitted by Class B subject to the following conditions - (a) the materials used in any exterior work shall be of a similar appearance to those used in the construction of the exterior of the existing dwellinghouse This condition is intended to ensure that any addition or alteration to a roof for a loft conversion results in an appearance that minimises visual impact and is sympathetic to the existing house. This means that the materials used should be of similar visual appearance to those in the existing house, but does not mean that they need to be the same materials or match exactly. The visual impacts of the materials used will the most important consideration. For example: • the flat roofs of dormer windows will not normally have any visual impact and so, in this case, the use of materials such as felt, lead or zinc for flat roofs of dormers will therefore be acceptable. • the face and sides of a dormer window should be finished using materials that give a similar visual appearance to existing house. So the materials used for facing a dormer should appear to be of similar colour and design to the materials used in the main roof of the house when viewed from ground level. Window frames should also be similar to those in the existing house in terms of their colour and overall shape. (b) the enlargement shall be constructed so that – (i) other than in the case of a hip-to-gable enlargement or an enlargement which joins the original roof to the roof of a rear or side extension – (aa) the eaves of the original roof are maintained or reinstated; and (bb) the edge of the enlargement closest to the eaves of the original roof shall, so far as practicable, be not less than 0.2 metres from the eaves, measured along the roof slope from the outside edge of the eaves; and (ii) other than in the case of an enlargement which joins the original roof to the roof of a rear or side extension, no part of the enlargement extends beyond the outside face of any external wall of the original dwellinghouse It is sometimes necessary to remove the eaves of the original roof wPD technical guidance, Class B · official source →