Wrap around extensions and the Class A limits

A wrap around extension has to satisfy the rear limits and the side limits of Class A at the same time, and the side element is what usually fails. Under Part 1 of Schedule 2 to the Town and Country Planning (General Permitted Development) (England) Order 2015, a side extension must be single storey, no more than 4 metres high, and no wider than half the width of the original dwellinghouse. A wrap around extension planning question therefore begins with a tape measure on the front of the house rather than with the rear garden.

The second thing that catches people is that the larger home extension route, the one giving 6 metres of depth on a terrace or semi through prior approval, applies only to rear extensions. Wrap the extension round the side and that route closes.

How the rear and side limits interact

Take the two elements separately and apply both sets of limits to the relevant part.

For the rear element on a terraced or semi-detached house, a single storey extension may project 3 metres beyond the rear wall of the original house, or 4 metres on a detached house, with a maximum height of 4 metres. The prior approval route doubles those depths to 6 and 8 metres, subject to a neighbour consultation process, and only for extensions that do not also extend beyond a side wall.

For the side element, the extension must be single storey, no more than 4 metres high, and no more than half the width of the original dwellinghouse. That last figure is measured against the original house, not against the house as it stands today.

Where the two meet in an L, every part has to comply with the limits that apply to it. A 3 metre rear projection with a side element 2.5 metres wide on a house originally 6 metres wide works. The same rear projection with a side element 3.5 metres wide does not, because it exceeds half the original width.

Width restrictions on the side element

Measure the original dwellinghouse at its widest point on the elevation the side extension will sit against, and halve it. That is your maximum.

Two mistakes recur. Measuring the house as extended, which is wrong and generous. And measuring the plot rather than the building, which is wrong and much more generous.

On a typical two bedroom terrace around 5 metres wide, the side element cannot exceed 2.5 metres, which after wall thicknesses gives an internal width of about 2.2 metres. That is a corridor, a utility or a widened kitchen, not a room. If you need more than that, you are applying for permission, and knowing so on day one changes the whole design conversation.

Article 2(3) land removes the side extension entirely. In a conservation area, a National Park, a National Landscape, the Broads or a World Heritage Site, Class A does not permit any extension beyond a side wall of the original dwellinghouse, so a wrap around is never permitted development in those areas.

Height at the eaves next to a boundary

Within 2 metres of a boundary of the curtilage, the eaves height of the extension must not exceed 3 metres. On a wrap around this bites twice, because both the side element and the flank of the rear element are usually close to a boundary.

The practical consequence is a flat roof or a low mono-pitch along the boundary edge, with any height gained towards the middle of the plot. It is also the reason so many wrap arounds end up with a flat roof and rooflights rather than a pitched roof, and why the internal ceiling height at the perimeter can be disappointing if nobody checked the levels first.

Measure from the highest ground level next to the building, not from the internal floor. On a sloping plot that distinction can be several hundred millimetres, which is the difference between complying and not.

Cumulative effect of earlier extensions

Class A is cumulative. The limits apply to the enlarged house as a whole, which means any previous extension counts against your allowance even if it was built by someone else forty years ago.

A house with an existing 2 metre rear addition has 1 metre of remaining depth under the ordinary rear limit, not 3. A house with an existing side addition of a quarter of its original width has a quarter left. And separately, the total area of ground covered by buildings within the curtilage, excluding the original house, must not exceed half the area of the curtilage, which catches large gardens with outbuildings less often than it catches small ones with a garage and a shed.

Check the planning history before you draw. Historic aerial imagery, the council's online register and the title plan will usually tell you what was there and when.

The original dwellinghouse and why it matters

Original means the house as it was first built, or as it stood on 1 July 1948 for anything older. Not as you bought it, and not as the previous owner left it.

This is the definition that decides the side width calculation and the cumulative rear depth, and it is the one most often got wrong. A 1930s semi that was widened in 1975 is measured on its 1930s width.

Where the history is unclear, a Lawful Development Certificate for proposed works under section 192 of the Town and Country Planning Act 1990 is the way to get the council's formal view before spending money. It is the only formal way to confirm that works are lawful, and it is worth having on any wrap around, because the calculation is exactly the sort of thing a buyer's conveyancer will query.

Design of the resulting rear elevation

A compliant wrap around is not automatically a good one. The elevation that results is usually long, low and flat roofed, running the full width of the plot, and it can read as a lean-to if the glazing and the roof edge are not handled with care.

Three moves help. Break the roof line, with a raised section or a rooflight run over the deeper part. Vary the glazing rather than running one continuous band of bifolds. And keep a proportion of solid wall at the junction with the original house so the old rear elevation stays legible.

Materials matter for compliance as well as for looks. Class A requires materials of similar appearance to the existing house for exterior work, and the materials of similar appearance test applies to a wrap around as much as to anything else. A dark grey render wrap on a red brick semi is not obviously similar in appearance.

Deciding between permitted development and an application

Go the permitted development route where the calculations work with room to spare, where the planning history is clear, and where the neighbours are not a concern. Certainty is fast and free of policy argument.

Apply where any of the following is true: the side element needs to be wider than half the original width, the house is on article 2(3) land, the eaves cannot come down to 3 metres near the boundary, the cumulative position is unclear, or the design you actually want breaks a limit by a small margin. A householder application takes eight weeks and gives you the design rather than the compromise.

A Planning Statement explaining the relationship to neighbouring gardens and the daylight position does most of the persuading on a householder application, and on a terrace the side return infill analysis is the closest comparison for the side element. A formal Design and Access Statement is not required for most householder applications, though a page of design reasoning attached to the drawings serves the same purpose.

This is general guidance, not legal advice. Permitted development rights vary with designations, conditions and Article 4 directions, so check the position with your local planning authority or a qualified professional before relying on it.

Enter your postcode on PlanScope to see which documents your extension is likely to need. Reports should be reviewed before submission, and we do not guarantee planning approval.