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Everything you need to know about loft conversions

Published on: 05 Oct, 2017

Loft Conversions smlConverting and extending your roof can be a very cost effective way of creating additional living space in your home. Unlike an extension to the main body of the building it does not take up valuable garden space or other land surrounding the property. Consequently, on smaller sites, where space for extensions is limited, it can be the only option.

The most straightforward method of conversion is to install roof lights which provide both natural light and ventilation. However, to increase the amount of useable floor area and headroom you could consider the construction of a dormer window or a hipped-to-gable roof extension.

A dormer is a roofed structure, usually containing a window, which projects vertically beyond the roof plane of a pitched roof. They come in a variety of sizes and styles and can range from large box type structures to more modest additions with pitched roofs.

Alternatively, a hipped-to-gable addition extends the ridge line of the existing roof out in line with the flank wall of the original building. The existing flank wall is then built-up to meet the extended ridge, creating a gable end.

In some cases, it may be possible to carry out roof alterations and extensions without the need for formal planning permission, under what are called ‘Permitted Development Rights’. These Rights derive from a general planning permission granted not by the Local Authority but by Parliament. However, it is important to seek professional advice beforehand, and you must comply with the specified criteria.

For roof lights this criteria comprises the following:-

  • The alteration (roof light) must not protrude more than 0.15 metres beyond the plane of the roof slope of the original roof
  • It must not project above the highest part of the existing roof (excluding the chimney)
  • It must not consist of, or include, the installation, alteration or replacement of a chimney, flue, soil and vent pipe, or solar panels or solar thermal equipment
  • Any new side-facing windows must be obscure-glazed and any opening part of the window must be at least 1.7 metres above the internal floor level

Likewise, for dormer windows and hipped-to-gable roof extensions the following criteria is applicable:-

  • No extension is allowed to be higher than the highest part of the existing roof (excluding the chimney)
  • No extension is permitted beyond the plane of the existing roof slope of the principal elevation that fronts the highway
  • The extensions cannot exceed 40 cubic metres, including any existing extensions to the roof which have been added previously, for terraced houses, or 50 cubic metres detached and semi-detached dwellings
  • No verandas, balconies or raised platforms are allowed
  • Roof extensions are not possible under Permitted Development in designated areas – this includes Conservation Areas, Areas of Outstanding Natural Beauty and National Parks
  • Materials must be similar in appearance to the existing house
  • Roof extensions, apart from hipped-to-gable additions, need to be set back, as far as practicable, at least 20 centimetres from the original eaves of the dwelling. In all cases the eaves of the original roof must be maintained
  • The roof enlargement cannot overhang the outer face of the wall of the original house
  • Any new side-facing windows must be obscure-glazed and any opening part of the window must be at least 1.7 metres above the internal floor level

As set out above, it is not possible to extend your roof under Permitted Development if you live within a Conservation Area, however, it may be possible to install roof lights. Similarly, if your property is Listed or is a flat, it will not benefit from Permitted Development Rights and, therefore, formal planning permission will be required for all alterations and extensions.

It is important to check that your property has Permitted Development Rights before you undertake any work, as in some cases these may have been withdrawn. Likewise, I would always recommend that you apply to the Local Planning Authority for what is called a Certificate of Lawfulness beforehand.

This form of application asks the Council to confirm that what you want to build complies with all of the relevant Permitted Development criteria and, therefore, does not need formal planning permission. This is particularly important if you are planning to build a large box type dormer window as in many cases the Council would not approve this form of extension if you applied for it under planning permission. The certificate issued by the Council is a legal document and can be used if you sell your property in the future to prove that the extensions were lawful and did not require formal planning permission at the time they were built.

Should you require formal planning permission for your proposal it is important to consider the size and scale of the roof extensions to ensure they do not dominate the building or existing roof scape. Most Local Planning Authorities have specific guidance and policies which guard against the construction of large box type dormer windows and other forms of roof extensions. In specific respect to St Albans the Council has a Design Guide for residential extensions –‘Extensions in Residential Areas: A Design Guide’. I recommend that you read this document before considering any extensions to your home, not just loft conversions, and also the specific design policies within the Council’s Local Plan, all of which are available on their website.

For information on whether your property has Permitted Development Rights and for advice on the correct application route for your proposal please contact Andrew Boothby on 01442 874087 or via email at for further assistance.

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