If you want to put up small detached buildings such as a garden hobby room, gym, store room 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 with substantially non combustible materials.
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.
For more information, please refer to the goverment planning and building regulations portal at www.planningportal.co.uk