Generally if a building is over 2.5m in height and closer than 2m to your boundary you will need planning permission.
Other factors may also influence whether you need permission such as the amount of plot you are taking up, the position relative to your boundary, the use of the building and services provided within it. Your local area and the interpretations of you local planning office.
We have an article in Richard's blog that may help more: Planning Permission
The best advice we can give is to always check with your local planning office if you have any doubts or concerns.
Answers to most questions can also be found by typing into the search bar in the widget or our info center or please contact us to help you further with any questions you have.