We are nearing completion of our self build and one of the last major tasks is to install the soakaway for rainwater. Prior to starting our build we had to carry out a percolation test and provide a scheme for dealing with the surface water and this was submitted and Discharge of Condition was approved by the Council as part of our PP. However, our percolation test result required a whooping 40m3 of soakaways to cater for a roof size of 120m2 plus 45m2 for the double garage. I've spoken to the firm who carried out the calculations a couple of times and they verified their calcs are correct. Installing a green roof or rain harvesting tank would not offset this at all. Building control will return to check for underground drainage of pipes and inspection chambers but are not really interested in the number of crates installed. My question is: when does planning get involved with this? Do they check what is installed before I cover over....?