I have a external stand alone garage which is 6m x 2.5m, 2.2m high with a flat roof and would like to replace it with a 8m x 3.5m with a 3.5m gable roof, one of the existing walls it the on the boundary to next door as would the new one be, do external buildings come under the new permitted builds or would I have to have planning permission? It is on the rear of the house. Next door do not have a problem as they are extending their house along the same boundary I would just like to know where I stand legally please and or what to do next?