Do you need planning permission for a side return extension?

The side return is the narrow strip beside the back addition of a Victorian or Edwardian terrace. Filling it in is one of the most popular ways to get a bigger kitchen in London. Whether you need planning permission depends on the house, how big the extension is and where you live. Some side returns can be built under permitted development. Plenty of London ones can't, especially in conservation areas or where the extension wraps around the back.

The permitted development rules that apply

A side return infill sits beside a side wall of the house and beyond its back wall, so it has to meet the rules for both. The government's technical guidance says that where an extension fills the area between a side elevation and a rear wall, the restrictions on both apply. In practice, to go ahead without planning permission it must:

• be single storey and no more than 4 metres high
• be no wider than half the width of the original house, measured at its widest point
• extend no more than 3 metres beyond the back wall of the original house on a terrace or semi (4 metres if detached), or up to 6 metres (8 metres if detached) through the prior approval process
• keep the eaves to 3 metres or less if it's within 2 metres of a boundary, which a side return almost always is
• use materials similar in appearance to the existing house
• together with other extensions and outbuildings, cover no more than half the land around the original house

"Original house" means the house as it was first built, or as it stood on 1 July 1948 if it's older. Earlier extensions count towards these limits.

When you will need planning permission

• Conservation areas. On this kind of protected land, all side extensions need householder planning permission, and the prior approval route isn't available.
• Wraparound extensions. An L-shaped extension that fills the side return and also runs across the back of the house is usually wider than half the house, so it needs planning.
• Flats and maisonettes. They don't have householder permitted development rights.
• Article 4 directions. Some councils have removed permitted development rights on certain streets, and some older planning permissions remove them by condition.
• Listed buildings. These need listed building consent as well.
• Anything over the limits above, including going more than one storey.

Check before you build

If you're relying on permitted development, apply for a lawful development certificate. It confirms the council agrees the work is lawful, it should be decided within eight weeks, and it costs half the normal planning fee. It's also useful to have when you come to sell.

If the extension goes beyond 3 metres past the back wall, you can use prior approval instead of a full application. The council consults your neighbours and has 42 days to decide. A full householder application normally takes eight weeks from when it's validated, including a 21-day consultation.

Party wall notices

Side returns are built right up to the boundary, so they almost always involve the Party Wall Act. You'll usually need to serve notice on your neighbours:

• at least one month before building a new wall on the boundary line
• at least one month before digging foundations close to their house (within 3 metres and deeper than their foundations)
• at least two months before work to an existing party wall, such as cutting in steels

Your neighbours have 14 days to respond. If they don't, it's treated as a dispute and surveyors are appointed, which can add weeks. A notice lasts a year. On our Latimer Road job we spoke to the neighbours early, which kept things moving.

Building regulations

Whatever the planning route, a side return needs building regulations approval for the foundations, steels, insulation, drainage and glazing. With a full plans application, the council has five weeks to decide, which can be extended to two months. You can run this alongside planning to save time.

What our side return extensions have cost

Both needed steels across the full width of the house. Glazing, the kitchen and how much of the rest of the house you refurbish at the same time make the biggest difference to the final figure.

Common questions