Backfilling hole for laying lawn
I've pulled up some rotten decking in our small garden with the intention of laying lawn. From what I can gather from the internet, I need a depth of 10-15cm topsoil but I have a hole of 32cm depth to fill. The good news is the whole area is only approx 2mx2m. The hole is a concrete basin which appears to be broken open, presumably for drainage, in the centre. I'm aware that I need to let the topsoil settle for 6-8weeks before laying the lawn so am eager to get going but I've no idea how to fill the gap. Can anyone guide me in the right direction?