Can anyone offer me some advice on the best way to build up my floor level for UFH installation? I have removed the old suspended timber floor on the ground floor level as it was rotten, I now have a void of 330mm to fill to make up the floor level. The house has a concrete base level which runs all the way through already. I had planned to use some hardcore then soft sand, Damp proof membrane then insulation and UFH screed. but the building inspector did not like this plan and sa