Permitted Development: the basics

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Not sure what you can and can't build without planning consent? Mike Dade sets out the facts
modern single story extension

What’s permitted?

Despite delays to changes in the law covering permitted development rights, the government has revealed the likely shape of things to come. The old system persists until the law changes and any works started before the change will not be affected by it.

Current development rights are complex, open to interpretation and a source of misunderstanding and frustration. Simplification has long been on the cards, so is the new system the streamlined model of simplicity we’ve been waiting for? Sadly, no. What’s emerged so far is a complex set of rules that look open to all the criticisms levied at the old system. No doubt, when the new law comes in - and the exact date is not fixed as we go to press - there’ll be more guidance on interpreting its provisions. Meanwhile, this is how it looks:

House extensions

The good news here is that the old reliance on calculating and comparing the volume of the existing building and the extension has been dropped in favour of a prescriptive, linear approach, based purely on the distance an extension protrudes from the building. So, no more complicated maths to be done but there are winners and losers as a result. Maximum sizes and heights for rear and side extensions apply, regardless of the size of the original house. Owners of small houses will benefit proportionately more than those of large ones.

These rules appear to be based around the notion of a standard-house and the one-size-fits-all approach will make for some interesting outcomes when applied to ‘non-standard’ arrangements.

For example, for an isolated house in the countryside, being restricted to a single storey for a side extension but allowed two or more stories to the rear makes no logical sense.

As before, the rules are less generous in ‘designated areas’. This will probably mean conservation areas, Areas of Outstanding Natural Beauty and National Parks.

Roofs and loft conversions

Some media reports have wrongly indicated that the new regime will bring in the possibility of loft conversions without the need for planning permission. Loft conversions have never needed planning permission, it’s only externally visible works altering or extending a roof that do. As with extensions, the old system relied on complex calculations of volume (tricky when you have odd roof shapes). Sadly, the new system relies on calculations of volume as well!

A new provision that roof extensions must start a minimum 20cm above the eaves looks set to produce some unusual designs but otherwise the new regime is broadly similar to the old. For external roof alterations, the rules are now more flexible to allow for things like solar panels and protruding rooflights on front-facing roof elevations, except, inevitably, in designated areas.

Garden buildings

Here the new system is again similar to the old but with a few extra provisions thrown in for good measure. There’s now a maximum eaves height as well as ridge height restrictions, and, importantly, overall limits on the amount (in square metres) of outbuildings allowed before a need for planning permission kicks in. With the limits set at 20m square metres for smaller gardens and 30 square metres for larger, this is a radical reduction in previous allowances.

The reference to a limit of 10 square metres for outbuildings, garages and swimming pools more than 20 metres from the house in designated areas is an interesting one. What kind of garage or swimming pool has a footprint of 10 square metres – that’s say 5 metres by 2 metres - who would build a garage that barely offers enough room for a car before the doors are opened, or a pool not much bigger than a bath?

The guidance released so far doesn’t mention the vital question of what you can use a garden outbuilding for; clarification of this sometimes contentious area would be helpful.

House extensions

  • No extension forward of the principal elevation or side elevation facing onto and visible from a highway

  • Maximum depth of a single-storey rear extension of 3m for an attached house and 4m for a detached house

  • Maximum depth of a rear extension of more than one storey of 3m including ground floor

  • Maximum eaves height of extension 3m within 2m of boundary

  • Maximum eaves and ridge height of extension no higher than existing house

  • Side extensions to be single storey with maximum height of 4m and width no more than half that of the original house

  • Two-storey extensions no closer than 7m to rear boundary or existing rear wall if closer than seven metres to boundary

  • Roof pitch of extensions higher than one storey to match existing house

  • Side-facing windows above one storey to be obscure-glazed; top opening allowed

  • Materials to match existing house

  • Maximum 50 per cent coverage of garden

Loft alterations and extensions

  • 40 cu m loft extension for terraced houses

  • 50 cu m loft extension for semi-detached/detached houses

  • Extensions must start a minimum of 0.2m above the eaves to maintain the visual appearance of a roof line

  • No extension beyond the plane of the existing roof slope fronting the highway

  • No extension to be higher than the ridge

  • No raised terraces, verandas or balconies

  • Side-facing windows to be obscure-glazed; top opening allowed

Roof alterations

  • Alterations should not project more than 150mm from the existing roof plane

  • No automatic right to build above the ridge of the building

  • No restriction on the percentage of the roof that can be altered

Garden outbuildings

  • No outbuilding, garage or swimming pool forward of the principal elevation

  • Outbuildings and garages to be single storey with maximum eaves height 2.5m and maximum overall height of 4m with a dual pitched roof (3m with mono-pitched roof)

  • Maximum height 2.5m within 2m of boundary

  • Maximum coverage of garages and outbuildings 30 sq m if garden covers more than 100 sq m or 20 sq m if the garden is less than 100 sq m

  • No raised terraces, verandas or balconies to be added to the house

  • Maximum 50 per cent coverage of garden


It looks like we’ve swapped one set of complex and somewhat random rules for another. But the devil will be in the detail and there’s much explanation and clarification to be done that could reveal constraints or opportunities not obvious at present. One vital question for extensions is what is the starting point against which to judge increases in size? The old rules referred to the building as it stood in 1948 or as built, if built since. Given that it’s becoming increasingly difficult to find out exactly what a house looked like 60 years ago, some updated reference point would be welcome.

All home owners contemplating extensions, alterations or works/buildings in their garden would be well advised to check both the current and the new rules carefully. For some, the new rules will allow bigger changes and for others, smaller. Make sure you know which applies to you and bring forward, or delay your project accordingly.

Remember, even if changes to your house don’t need planning permission, they probably need Building Regulations approval. Always check before you start work!

Caption: Extensions can be allowed under permitted development rights, provided they fit within the criteria

Photo credit: Alistair Nicholls

Also related to this article


Posted on

Thanks for the 'overview' Mike - before people go dashing off and start to construct 'Garden buildings' perhaps you'd also care to mention the bit that most homeowners, architects and 'agents' fall foul of!? And that is that permitted development for such buildings is further encumbered by a requirement that the proposed building is for a purpose 'incidental to the enjoyment of the dwellinghouse as such' - and that can be a whole new unexpected can of worms to deal with.

For those less enlightened as to the pitfalls to avoid I'd recommend you 'Google' "Incidental to enjoyment of dwellinghouse" and entertain yourselves with that conundrum for a while.

Posted on

Hi Rick, thanks for highlighting this contentious grey area.

As I understand it, the phrase 'incidental to the enjoyment of the dwellinghouse as such' is intended to prevent outbuildings being added as a means to creating what would be considered as 'primary' (part of the main house) or self-contained living space (i.e. permanent bedrooms, living rooms and kitchens). It also rules out creating holiday lets without planning permission.

So things like storage sheds, garages, workshops, home offices and greenhouses can all be considered permitted development provided they're within the parameters set.

It seems that living/sleeping quarters can be acceptable under PD rights provided they're clearly used as 'guest' accommodation. That's likely to translate into the 'annexe' or guest unit having no kitchen and being small enough that it wouldn't be possible to add facilities such as a kitchen at a later date.

The reason for this is that planners are wary of homeowners adding large outbuildings that could be subject to a change of use at a later date; thereby circumventing the system by setting in motion the opportunity for 'infilling' a new house on a plot that wouldn't normally have received planning permission for such a development.

It's certainly a muddy area and can seem punishing to those who really do want to build 'incidental' accommodation - but planners have to consider what future owners might do, as well as whether you might change your mind later! As always, it's a good idea to ask your local authority or a local planning consultant for their advice - taking a look at appeal cases in your area may help clarify things.

Posted on

Confusing isn't it? sign up for a trial period to; dcponlineDOTcoDOTuk and search for "incidental to enjoyment"..

(1) A LDC seeking confirmation that a building erected within a garden, was capable of being occupied by family members associated with the dwellinghouse, was rejected with a full award of costs to the council. The appellant claimed that Class E permitted the erection of a building within the curtilage of a dwellinghouse for a "purpose incidental to the enjoyment of the dwellinghouse as such." Accordingly its use for sleeping and eating as an annexe to the main house but not independently occupied from it, was permitted development.

The inspector noted previous court judgments where this matter had been tested including Peche D'Or Investments v SOS [1996] and Rambridge v SOS and East Hertfordshire D.C. [1997]. These judgements supported the view that accommodation put to a purpose integral to the ordinary residential use of the dwellinghouse would not be considered to be incidental and therefore not permitted by Class E.

There was no basis for disagreeing with the High Court judgements and the inspector dismissed the appeal.

(2) A lawful development certificate was sought with regard to whether an outbuilding which could be erected under Class E could lawfully be used as a residential annexe upon its completion without any intervening use.

The appellant argued that previous court judgements which held that Class E rights did not extend to primary residential accommodation even where it was associated with the primary use of a main dwellinghouse, had been wrongly decided. Instead, the appellant argued in accordance with Williams v Minister of Housing and Local Government [1967] that an incidental use was an incident in the life of a planning unit and therefore in accordance with Wood v Minister of Housing [1973], what was built under a development order became part of the existing planning unit and could have the same character as to be found within the planning unit as a whole. Therefore ancillary residential use would be classed as being incidental to the lawful use of the whole planning unit as a dwellinghouse.

The inspector rejected this approach and in citing the dictionary definition of "incidental", he noted that it referred to something being of casual or secondary importance which fitted well with the most recent court judgements where it was held that primary residential accommodation in a curtilage outbuilding would not be expected to be incidental to the enjoyment of the dwellinghouse as such. A lawful development certificate was denied.

Posted on


We're nearing completion on a purchase of a bungalow. The bungalow is in green belt (is Green Belt considered a designated area?). The owners applied for and were granted planning permission for a single story extension. Although it has since expired as no footing were laid. I think they did this to be on the "safe side" as the extension is only 35m2 and therefore does not extend beyond (current) PD rights.

The property has a 15m2 conservatory (with separate planning) and a small 9m2 extension. Both built withing the last 10 years. According to the plans, the extension will replace the conservatory and existing extension, therefore we will only gain an additional 11m2 and loose a lovely conservatory.

There is a lot of talk of PD, but I am happy to forget the PD and go for old fashioned planning permission, creating an extension with a 1st floor and keeping the conservatory. From what I can glean from various Council papers, raising the ridge height in Green Belt is a big no no, however, I can create enough head room for a 1st floor by lowering the ground floor by 800mm.

Am I correct in forgetting PD and applying for full PP in an attempt to get what we want?

Many thanks

Posted on


I own a plot of land (field) which once had a cottage on it. It was demploished in 1939, leaving evidence of 3 walls. Can anybody advise if it is possible to rebuild. The plot is in open countryside and away from the village boundary.

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