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  4. Home Extensions Part Two: A Guide to Planning Permission and Building Regulations

Building

Expert advice on structural work, home extensions, renovations and understanding building regulations.

Building

Home Extensions Part Two: A Guide to Planning Permission and Building Regulations

You may think that making the decision to invest in an extension, then researching the different extensions available to you are the key steps in transforming your home. However, with most major decisions, there is at least some red tape, and home improvements are no exception. Before you start building extensions, converting garages, or knocking down walls, you may need to get the right permissions. Here’s what you need to know.

You may think that making the decision to invest in an extension, then researching the different extensions available to you are the key steps in transforming your home. However, with most major decisions, there is at least some red tape, and home improvements are no exception. Before you start building extensions, converting garages, or knocking down walls, you may need to get the right permissions. Here’s what you need to know.

Permitted development rights

Permitted development rights mean that you are allowed to extend your home or renovate it without having to submit a full (and often expensive and time-consuming) planning application. The last few years have seen changes in permitted development rights which mean that homeowners are able to undertake a wide range of home improvements without negotiating planning permission. These include:

Two-storey extension – until recently, this would have needed planning permission. A two-storey extension adds upstairs and ground floor space. One of the most common two-storey extensions is to double the size of the kitchen downstairs to give a large, open-plan space downstairs, and an extra bedroom or bathroom (or both) upstairs. In order to build a two-storey extension without needing planning permission, it must:

  • Be a rear extension
  • Not take up more than half of the land around the original house (including sheds and any other outbuildings)
  • Be made of materials that match the exterior of the house
  • Not go beyond 3m of the original wall, or within 7m of a boundary opposite the rear wall
  • Not be taller than the original house
  • Not be more than 3.5m higher than the next tallest terrace (for terraced properties)
  • Not have balconies or verandas
  • Not have clear or opening upper floor side windows (any side windows on the upper floor should be privacy glazed and non-opening).

Side extensions of more than one storey must have planning permission, and these rights do not apply to single-storey buildings.

A new storey – since 2020, it is possible to add a new storey to your home, providing you meet a range of caveats, including that the new storey must be no more than 3.5 m higher than the next tallest terrace.

Loft conversion – permitted rights allow you to convert your loft space and add a new dormer, up to 50m3 for detached properties and 40m3 for terraced.

Side extension – single-storey side extensions are a great way of extending your property without losing valuable garden space, as they often absorb rarely-used side alley space. If you are considering a wraparound extension to the side and rear, you will need planning permission.

Garages and outbuildings – you can usually convert a garage without planning permission, unless parking is an issue in your area, in which case there may be local restrictions (check with your local authority). Outbuildings and garden rooms offer a great way of adding space, but if you plan on using them as a bedroom rather than a gym, playhouse, office space or tv room, for example, you may need planning permission.

If you are unsure about what you are allowed to do, ask your builder or architect, or give your local authority a call. Next week, we discuss finding an architect; follow us on X or Facebook to avoid missing it.

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Find clear, practical answers to common building questions, helping homeowners understand everyday issues, know what checks they can carry out safely, and when it is best to contact a qualified professional.

  • Do I need planning permission for a home extension?

    Plenty of extensions don't need planning permission - they fall under Permitted Development. Whether yours qualifies depends on the size, location, and type of build. Single-storey rear extensions up to four metres on a detached house often get the green light, but side extensions, two-storey builds, and properties in conservation areas usually do need permission. Always check with your local planning authority before you start - building without the right approvals can mean being made to undo it all.

  • What is involved in building a conservatory?

    You're looking at groundworks and foundations, the frame and glazing, the roof, and then the internal fit-out - flooring, heating, electrics. Most conservatories under a certain size fall under Permitted Development, but they still need to comply with Building Regulations, especially if you want to use the space as a proper room year-round. On the roof: solid or tiled options make a huge difference to usability - traditional polycarbonate can be unbearably hot in summer and freezing in winter. Most projects take two to six weeks.

  • Do I need a structural engineer for my home renovation?

    Not for everything - but if structural changes are involved, yes. Removing a load-bearing wall, putting in a steel beam, touching the roof structure, or adding a sizeable extension all need a structural engineer to design the solution and produce the calculations for Building Regulations approval. A builder might tell you whether a wall is load-bearing, but only a structural engineer can specify the right beam and carry professional liability for that advice.

  • Do I need planning permission to install patio doors?

    Usually not, if you're replacing an existing door or window in the same opening - that typically falls under Permitted Development. But if you're making the opening larger or creating a new one in an external wall, you may need planning permission or Building Regulations approval. Conservation areas, listed buildings, and properties with an Article 4 Direction have tighter rules, so check before assuming. Any structural work to the opening, like fitting a new lintel, needs Building Regs sign-off regardless.

  • Does my extension need Building Regulations approval even without planning permission?

    Almost always, yes. Planning permission and Building Regulations are two separate things. Extensions need to meet regulations covering structural integrity, fire safety, insulation, ventilation, and drainage - regardless of whether you needed planning approval. Your local authority's building control team can confirm exactly what's required. And don't skip it - missing Building Regs sign-off can cause real headaches when you come to sell.

  • How long does a typical home extension take?

    A small single-storey extension usually takes eight to twelve weeks from groundworks to completion. Add several months if planning permission is needed before work can even begin. Bigger builds - two-storey additions or anything needing significant structural work - can take four to six months or more. Get a realistic timeline from your builder upfront, and factor in a buffer for the unexpected.

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