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Permitted development - expansion to guidelines

Changes to The Town and Country Planning (General Permitted Development) Order 1995 came in to force on 1st October 2008. The changes mean that most householders planning extensions or loft conversions will not need to make an application for planning permission.

The number of planning applications for domestic extensions has grown steadily since the start of the last property boom in 1995. Planning Departments have been struggling to process applications, expected to number around 330,000 in the current year, within the target 8 week period. The new regulations are expected to remove around 25% of applications from the planning system.

The most significant changes are outlined below:

Detached Houses

Single storey rear additions, measuring up to 4 metres deep and 4 metres high, may be added to detached properties without planning permission. Where extensions are 2 or more storeys high the permitted depth is reduced to 3 metres and the height must be no greater than the roofline of the existing property. These measurements replace the former volume caps.

For loft conversions the volume caps remain in place, principally as a way of preventing householders from adding overbearing extensions, although they are no longer related to the volume of the original property. Previously extensions were not permitted if they added more than 15% to the volume of a house. The volume cap is now set at a straightforward 50 cubic metres on detached properties.

Semi-detached & Terraced Houses

On semi-detached and terraced properties the maximum depth for all rear extensions is set at 3 metres and the volume that can be added to roof spaces is capped at 40 cubic meters.

All Properties

Only single storey extensions are permitted to the side of a property and only then when they are no more than half the width of the original house. Dormers will not be permitted on elevations that face a highway and must not extend above the ridge of the original roof.

All references to the "original house" mean the house as it was first built or as it stood when the Town & Country Planning Act came in to force on 1st July 1948. Extensions added prior to that date do not affect Permitted Development rights.

Further restrictions will apply to properties within Conservation Areas and to listed buildings. In addition, local planning offices will still have the power to alter the allowances so if you are in any doubt the best advice is to contact your local planning office to discuss the proposals before commencing work.

All new extensions will still require Building Regulation approval and if the planned work will affect a shared wall, or involves excavating close to the boundary with a neighbour it will probably be covered by Party Wall etc Act 1996. Owners planning works which fall within the scope of the Act have an obligation to serve written notice on the adjoining owners.


The Government is attempting to use the planning system to tackle the growing problem of flooding caused by rainwater running off paved-over front gardens. As part of the package of measures which came into force on October 1st householders will require Planning Permission to add 5 square metres or more of paving to their front gardens. Where permeable materials are used that requirement will be removed and the work classed as a Permitted Development.

Acceptable materials include gravel, paving slabs with open joints, and concrete strips with drainage channels between. The over-riding requirement is that the surface water must drain away naturally within the curtilage of the property.

Prepared for Diyfixit by Justin Burns BSc MRICS of

Peter Barry Chartered Surveyors & Party Wall Consultants

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