If your property is a flat, maisonette, or a listed building, as planning permission is always required for these.
If your proposed garden room is in front of your house.
If your property is in a conservation area.
National Park or AONB: In such areas, verify the additional rules, allowing development within 20 meters of the house but restricting outside development to 10 square meters.
If the total area of all structures, including the proposed garden room, exceeds 50% of the total area of your garden.
If the garden room is within 2 meters of the boundary, confirm that its maximum height is 2.5 meters.
If that the eaves of the garden room are more than 2.5 meters above ground level.
If you plan to use your garden room as a living accommodation e.g. you want to sleep in it, have a kitchen and/or bathroom.
Building Regulations: For England and Wales, understand that Building Regulations might apply if the garden room is attached to the main home, has over 15 square meters of floor area with sleeping accommodation, or if you plan to use it for specific purposes like sleeping.