In the UK, planning permission is not always required for a summer house, but certain conditions must be met to avoid needing planning permission.If the summer house meets the following criteria, it is generally considered to be permitted development and does not require planning permission:The summer house is located within the property’s boundary and is not taller than 4 metres (or 3 metres if it has a flat roof).The summer house does not cover more than 50% of the total land area around the original house.The summer house is not used as living accommodation and is used for recreational purposes only.The summer house is not located in a conservation area, an area of outstanding natural beauty, a national park, or a site of historical interest.The summer house doesn’t have a raised platform or veranda of more than 30cm above ground level.It's important to note that these guidelines may vary depending on the specific location and circumstances, and it's always best to check with your local planning authority to confirm whether planning permission is required for your summer house project.