What Are The Planning Regulations For Garden Rooms?

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What are the rules around Garden Rooms?
Garden rooms are governed by the same set of regulations that cover all detached structures in the garden - sheds, workshops, kennels and garages. In planning circles all of those structures are called outbuildings and the regulations that govern outbuildings are defined in a set of legislation called the General Permitted Development Order or the GPDO. That's where the term PD rights comes from - General Permitted Development Order. You can find that on the gov.uk website, but be warned - those regulations are fairly opaque and difficult to interpret.
But thankfully there are other sources of information for permitted development rights, namely the Planning Portal website, which has an excellent interactive house and allows you to answer some of the basic questions around outbuildings.
It's important to state from the outset to establish if you have the rights to erect these outbuildings. Some examples of where you don't have those rights would be for; listed buildings, conservation areas have limited rights, Areas of Outstanding Natural Beauty (AONBs). But there could be fundamentally other reasons - for example you could live on a ground floor flat with a garden and you might think you can erect structures in the garden. In fact flats and maisonettes don't have any permitted development rights, and the same is also true of some houses that are built on a relatively modern estate - anything built in, say, the last 10 or 15 years. You shouldn't assume that you have your full permitted development rights.
Equally, a former occupier of your home 10, 20 or 30 years ago could have made an application - a seemingly unrelated application maybe - for a loft conversion, where the planning officer at that point in time considered it necessary - fairly or unfairly - to remove the permitted development rights to erect these structures. So don't make the assumption you have them. Obviously, many houses do - most do, to be fair - but don't make the assumption you have those rights. You can check those either with the council or by looking on the council's website and going back over your site history and finding out if there are conditions attached to a previous permission. But don't make the assumption that you have your full permitted development rights.
So back to the principal thrust of your question about Garden Rooms. They're governed by the GPDO. The type of structures we're talking about are called Class E buildings. Class A is to do with extensions etc, but Class E covers outbuildings and those rules are pretty generous.
In fairness to the government, their rules are pretty generous. You can erect buildings that cover up to 50% of the plot - that's excluding your house. Typically in the rear garden and the side garden, but the building has to be reasonably necessary. So just because you could build something that's the size of a primary school in your rear garden doesn't mean that you can, because it has to pass a reasonably necessary test.
Most of the buildings that I've seen erected for offices or a gym or that type of use in the back garden would easily pass that test, but there was an interesting case of a gentleman in 2016 who erected a 10,000 square foot leisure complex in his back garden, complete with cinema and bowling alley, that didn't meet the necessary test and the whole thing had to be removed. So it's always worth making that inquiry.
So the dimensions of the building are one set element, so you can have a building that's up to two and a half metres tall when it's less than two metres from the boundary, or up to three metres tall if it's more than two metres from the boundary, and like I say, that building can cover as much of the area as you consider necessary of your garden - but just bear in mind that reasonably necessary test.
But most people don't want to cover their garden in outbuildings - you want to use it for a specific purpose, such as an office, so in that sense you should be okay in that regard. Bear in mind also that you can apply for a certificate of lawfulness before or after you've had the building built and we often get inquiries very late in a conveyancing process where a client needs a documentation to prove that something didn't require planning permission. Of course that's a slight frustration and irony of the process - the government removing some of the red tape around outbuildings, then people end up having to make those applications at some point in the future.
So my advice certainly is to get permission in advance or have it confirmed as lawfully permitted development before you get to a position where you're looking to sell a property or let it out, or prove that permission wasn't required.
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Recorded February 2023. This content does not constitute formal advice from New Garden Room Company or Mark Doodes Planning.