Outbuildings Planning Permission + Building Regulations

Outbuildings Planning Permission

You are viewing guidance on England. Regulations for Scotland, Wales and N.Ireland may differ. The following information should be used as a guide only. We recommend that you contact your local Planning Authority for qualified advice.

Outbuildings such as log cabins, summerhouses, garden offices, garden gyms, workshops, sheds, greenhouses and garages do not require planning permission subject to certain limits and conditions. (outlined below). Building regulations may apply subject to building size. Please see Building Regulations

Under new regulations that came into effect on 1 October 2008 outbuildings are considered to be permitted development, not needing planning permission, subject to the following rules, limits and conditions:

[1] No outbuilding on land forward of a wall forming the principal elevation.
[2] Outbuildings and garages to be single storey with maximum eaves height of 2.5 metres
* and maximum overall height of four metres with a dual pitched roof (ie gable roof - peak in the centre, known as the ridge, and the roof slopes down either side) or three metres for any other roof (ie Pent or Mono roof - flat slanting roof).
[3] Maximum height of 2.5 metres
** in the case of a building, enclosure or container within two metres of a boundary of the curtilage of the dwellinghouse.
[4] No verandas, balconies or raised platforms.
[5] No more than half the area of land (50%) around the "original house"
*** would be covered by additions or other buildings.
[6] In National Parks, the Broads, Areas of Outstanding Natural Beauty and World Heritage Sites the maximum area to be covered by buildings, enclosures, containers and pools more than 20 metres from house to be limited to 10 square metres.
[7] On designated land
**** buildings, enclosures, containers and pools at the side of properties will require planning permission.
Within the curtilage of listed buildings any outbuilding will require planning permission.
[8] To be permitted development, any new building must not itself be seperate, self contained, living accommodation and must not have a microwave antenna.

*Since the introduction of RULE [2], most of our log cabins and summerhouses have been specifically designed so that the eaves do not exceed the '2.5m eaves height' threshold. You may still require planning permission subject to the size of your garden and where you intend on installing the building.

**If you plan on installing a building within 2 metres of a boundary, the cabin, greenhouse, shed etc must not exceed 2.5 metres in total height. If it does exceed a total height of 2.5m then you are not allowed to erect the building without planning permission. It is also worth noting that if you are looking at an outbuilding (log cabin, summerhouse etc) measuring 4x4m (width and depth), you would need to allow a footprint of 8x8m (width and depth) allowing for 2m clear space around the perimeter of the entire outbuilding.

***The term "original house" means the house as it was first built or as it stood on 1 July 1948 (if it was built before that date). Although you may not have built an extension to the house, a previous owner may have done so.

****Designated land includes national parks and the Broads, Areas of Outstanding Natural Beauty, conservation areas and World Heritage Sites.

Please note: the permitted development allowances described here apply to houses not flats, maisonettes or other buildings. Guidance on flats and maisonettes may differ.

Building Regulations

If you want to put up small detached buildings such as a garden shed or summerhouse in your garden, building regulations will not normally apply if the floor area of the building is less than 15 square metres and contains NO sleeping accommodation.

If the floor area of the building is between 15 square metres and 30 square metres, you will not normally be required to apply for building regulations approval providing that the building contains NO sleeping accommodation and is either at least one metre from any boundary or it is constructed of substantially non-combustible materials.

This section provides you with general information to help you comply with the Building Regulations when constructing a new outbuilding within the boundaries of an existing property, such as:

• garage or carport
• summerhouse or shed
• greenhouse

Building a new garage attached to an existing home would normally need building regulations approval.

Building a new attached carport (open on at least two sides) would not normally require building regulations approval if it is less than 30 square metres in floor area.

Building a detached garage of less than 30 square metres floor area would not normally need building regulations approval if:

• the floor area of the detached garage is less than 15 square metres.
• the floor area of the garage is between 15 square metres and 30 square metres, provided the garage is at least one metre from any boundary, or it is constructed from substantially non-combustible materials.
• If you want to convert an integral or attached garage into habitable use, building regulations will normally apply, view specific information for garage conversions.

In many cases, these structures will be exempt from requiring approval under the Building Regulations if they meet certain exemption criteria.

If the Regulations do apply to the building then it must be built to reasonable standards.

The following pages give an indication of some of the elements normally required to satisfy the requirements of the Regulations when building an outbuilding:

• Foundations
• Walls below ground
• Flooring


Foundations are required to transmit the load of the building safely to the ground. Therefore, all buildings should have adequate foundations (normally concrete), which will vary from one project to another depending on the circumstances of each case.

These foundations can be cast as deep-fill (filling most of the trench) or shallow-fill (where the minimum thickness to transfer the load to the soil is provided).

There are other types of foundations that may be used if the ground conditions do not make trench fill practicable. It is advisable to contact a structural engineer or speak to building control for further advice.

Factors to be taken into account of when designing a foundation:

Type of soil

The type of soil that the foundation will sit on is important for two reasons:

it should be able to bear the weight (load) of the foundation and the extension - different soils have different load bearing capabilities.
the way it reacts to variations in moisture content (such as in prolonged rainy or dry seasons) can lead to the soil expanding or contracting. This is a particular issue with some clay soils. These changes mainly occur up to a certain depth (typically about 0.75m) therefore foundations should be made deeper so they are not affected by ground movement (although see "Trees" below).
Adjacent structures

It is important to ensure that the excavation for the new foundation does not undermine adjacent structures. In general it is good practice to excavate at least to the same depth as the bottom of the foundation to the adjacent building. If the excavation runs alongside an existing footing then care will be needed - for example, by excavating and concreting the foundation in shorter sections to avoid undermining a whole length of an adjacent structure (see also guidance on the Party Wall Act).


Trees will draw moisture from the ground around them and beyond through their root system. As moisture is drawn from the ground it will have a tendency to shrink. How much the ground will shrink will depend on the following factors:

Type of soil - Clay soils shrink more than other types of soil. Therefore excessive movement of the ground could cause damage to the foundation and the structure it supports.
Size and type of tree - How large a tree or shrub will grow (its mature height), and the tree type will determine how much moisture it generally draws from the ground.
The presence of trees in clay soil areas can mean foundations need to be significantly deeper than might be first expected, although if the trees are far enough away, there may be no impact. Note: If existing trees are removed or significantly reduced in size, all or some of the moisture in the root system will be released over time into the soil and, if the soil is clay for example, could cause swelling of the soil and damage to nearby foundations and structure(s) supported.

Drains and sewers

As the weight (load) from the foundation of a building is transferred to the soil it spreads downwards outside the footprint of the foundation at a typical angle of 45 degrees. If a drain or sewer is within the area coveredby that 45 degrees area there is a risk that it could be affected by the load from the foundation and possibly crack. Therefore,the foundation excavation should normally be at least to the same depth as the bottom (invert) of the deepest part of the drain, sewer or its trench.

Size and construction of new building

The foundation will need to support more weight (load) from a two storey building compared to a single storey. This has a significant factor in determining design, particularly in respect of its depth and width. This is directly related to the bearing capacity of the soil supporting it. The width of the foundation is also governed by the wall thickness.

Ground condition

Generally the topsoil is taken away and good undisturbed ground is found i.e. ground that has not been built on. In some cases there are areas which have previously been backfilled, such as above where drains have been laid or to level a site, which consist generally of soft, mixed soil with foreign objects. The foundation can not be poured until undisturbed ground has been found.

Landfill sites

Some properties have been constructed on landfill sites which may require a more extensive form of foundation like piling as the depth of undisturbed ground could be many metres deep. An alternative may be a "raft" foundation. A structural engineer will be able to advise you further.

For health and safety reasons, care should be taken when working in trenches due to the risk of collapse causing potentially serious injury.

Walls below ground

Depending whether the foundation for a new detached building has been cast as deep-fill or shallow-fill, there could be a small or large amount of wall construction needed below ground level (referred to as substructure), on which the above ground walls (referred to as superstructure) will be built.

The principal requirement of the substructure is to ensure adequate support is provided to the superstructure. The substructure (bricks or blocks and mortar) should be effective and be resistant to frost and also to sulphates within the ground.



A floor will need to provide for one or more of the following:

• Structural support of the room's contents and users and the weight of the floor itself; and
• If the floor is a ground floor, provide resistance to:
• Ground moisture; and
• Heat loss (thermal insulation)

There are three general types of ground floor construction:

• Solid, ground bearing, concrete floor
• Suspended Timber Floor
• Suspended Concrete floor


A typical floor for a garage generally consists of hardcore, sand blinding, DPM (damp proof membrane) and concrete. It is considered to be good practice to place reinforced mesh within the concrete as this can reduce the chances of cracking from the load (weight) of a vehicle. The floor will not normally need to be insulated.

Storage buildings, annexes and summer houses

Floors in these types of building can take one of the three general types outlined above. The exact specification for the floor will depend on how the building is to be used and whether it is to be heated. More information on each floor type can be found in the section on floors for extensions.


Source © PlanningPortal.Gov This is an introductory guide and is not a definitive source of legal information.Click here for further information

This guidance relates to the planning regime for England. Policy in Scotland, Wales and N.Ireland may differ. We always recommend that you contact your Local Planning Authority for further information prior to planning your new external installation.

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