Permitted Development: The Basics

Not sure what you can and can't build without planning consent? Mike Dade sets out the facts
by Mike Dade
25th November 2012

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

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