When planning a loft conversion in |London it is not generally necessary to apply for planning permission, except when extending or altering a roof space to exceed specific limits and/or conditions.

These limits include:

  • For a terraced house, a 40 m³ volume allowance in added roof space
  • With detached or semi-detached properties, an allowance of 50 cm³ applies
  • Any extensions should be no higher than the existing high roof part and should be of materials resembling those of the current property
  • No raised platforms, balconies or verandas are allowed
  • Roof enlargements may not hang beyond the original house exterior walls

It is important to inform yourself of any relevant conditions or limits to your own particular building, as they may vary according to property and location. There are also different allowances for maisonettes, flats and any building other than houses in Londo.

When the intention is to convert the loft space into a bedroom or other habitable area, then building regulations approval will be necessary. For a two-storey house, London loft conversion the regulations are quite straightforward: the materials used for the new flooring must be sufficiently strong and structurally sound; the stability of an existing structure, including its roof, must not be compromised in any way; the stairs to the new space must be of safe design; there must be a safe fire escape, there should be sufficient sound insulation between the new and existing spaces. Anyone preparing to undertake this kind of conversion should contact Building Control for advice on keeping the building within regulations.

Other points to be taken into consideration are the properties load-bearing walls, which must be able to support any additional loads. This will be particularly important in homes that have an open plan ground floor, which will have a support beam in place of a central load-bearing wall. This beam will need to be of sufficient strength to hold any additional load from your loft conversion.

The need for a safe fire exit will normally mean that some adjustments may have to be made to other parts of the home, for instance fire resistant doors, or possibly partitions that protect the staircase; this of course must be a full or space-saving staircase, as ladders or retractable stairs will not be acceptable for the new conversion.
As well as checking the flooring materials are strong enough to support the new loads, it may be necessary to install new floor joists. This will depend upon the existing ceiling joints and the weight that they are designed to support.

This article is of course only intended as guidance and individuals should check for details in their own area, certainly if in different parts of the UK other than England. The details above are relevant to houses of one or two stories, and any other type of property will be subject to different regulations and limitations.

The Government provide a document giving technical guidance on permitted development to properties, which they suggest strongly that homeowners should read thoroughly:
Download ‘Permitted development for householders – Technical guidance‘.