You may need to apply for planning permission if you are changing the use of a building, or making alterations to the exterior of a building.  By reading some basic guidelines from the Office of the Deputy Prime Minister you can see where planning permission is required. 

Alternatively, you can contact Planning Services at Bristol City Council about your proposals - officers will tell you whether planning permission is required for your particular property.  The direct number for this department is 0117 922 3097.