I want to build an extension with a depth of 3.9 metres from the existing building. I have an Oak tree 11.5 metres from the existing building. I have worked out that that the Root Protection Area (RPA) is 4.8 metres around the tree from its centre. Therefore 11.5 - 4.8 = 6.7. So the edge of the RPA is 6.7 metres from the existing building, I only want to build out 3.9 metres so I have 2.8 metres leeway. My architect says I need planning permission because the tree has a TPO rather than Permitted development rights. Who's right. I know I have to protect the tree from damage