December

Polythene sheet (damp proof membrane) installed and sealed all round the edge.

Then 40mm of floor insulation.  I’d prefer more, but the low ceiling height is getting lower with every layer I add to the floor.  The other option would be break up the existing concrete floor and excavate down, and then install lots of more eco insulation and a new floor.  Sorry, but no.

It’s XPS – eXtruded PolyStyrene.  XPS is stronger than EPS (expanded polystyrene) so good for floors.  We previously used EPS for EWI.  This product is also grey, as it’s treated to be reflective and so even more insulating, to get more benefit in the limited thickness.  The insulation really matters here, because the floor will be heated, and there may not be any insulation at all between the existing concrete floor and the earth.