Outbuildings are considered to be permitted development, not needing planning permission, subject to the following limits and conditions:
No outbuilding on land forward of a wall forming the principal elevation.
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 or three metres for any other roof.
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.
No verandas, balconies or raised platforms.
No more than half the area of land around the "original house"* would be covered by additions or other buildings.
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.
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.
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.
Check for updates on gov plannig portal
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.
Building regs on gov planning portal