Quick question, for various reasons it looks like we need to increase the thickness of the floor on the oversight in our extension. Originally it was going to be 150mm - 100mm cellotex board with 50mm screed. It now looks like it will be nearer 172mm + the thickness of floor tiles - 20mm Newton membrane, 50mm insulation board, 2mm DPM, 25mm cellotex board, 75mm screed (to take pipes and UFH). Whilst there is enough head room, the finished level of the floor will be above the DPC in the inner leaf by 10mm or so..... is that a problem? The damp proofing specialist we just had in was sucking air through his teeth which has made me wonder! In fact because we are planning to put in water UFH we will be insulating around the edge of the screed as per normal practice so the screed slab won't touch the walls... if that makes any difference.