Making alterations to approved Planning Permission

I recently recieved planning permission for a house but I now want to make changes. basically I got planning for velux combi windows in roof but now I want to put in roof rights and decrease the ridge height by 200mm. I aso want to delete a porch and make the building 1m longer. On plan the foot print of the building is the same but the front and back elevation looks different. I have tried getting in contact with the planners but they seem to be on "go slow". If I have to go back in for planning do I have to do a new site suitability test etc?

Before offering you advice, would you mind if I asked whay you want to remove a porch and reduce a permitted ridge height?

ONQ.

ONG,

Sorry, porch is not been deleted and ridge height will not change. I have planning for VELUX combi windows where some of the windw is on the vertical face of the wall and the rest is on the roof. So main change is changing combi windows to roof lights to upstairs. Might I add that there are only 2 bedrooms upstairs and each bedroom has a window on the gable wall so this would satisfy fire escape requirements.

My seperate query is if I was to go back in for planning with a new design but with sae footprint, floor area etc would I have to get a new site suitability test carried out?