Building regulations are not always required. The following information has been taken from the Government’s Online Planning Portal.
If you want to put up a small detached building 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 15m2 and contains NO sleeping accommodation.
If the floor area of the building is between 15m2 and 30m2, you will not normally be required to apply for building regulation approval providing that the building contains NO sleeping accommodation and is either at least 1m from any boundary or is constructed of substantially non-combustible material.
These notes are for guidance only. We recommend that if you have any concerns over the above you consult with your Local Authority.