Help

I have a single storey kitchen extention attached to my house. I believe that it has been there about five years. I want to increase the wall thickness using brick and insulation on the outside. I will also have to increase the roof thickness/size to accomodate this. The question is do I need planning permission to do this. I am not sure that there is planning on the existing building, I believe that if the existing structure has been there for over four years, planning is not required. Your help would be appreciated. Best regards.