mesh of planks and bars criss-crossing each other. Below these planks, and in between the bars, there's a 100 mm thick layer of mineral wool, under which there's a folio acting as vapour barrier. The folio also makes the house airtight, which aides insulation. Below the folio are the electrical cables and then the ceiling panelling. Thus it is fairly dangerous to step onto the yellow mineral wool, since one might just crash down into the house. The photo above shows the first planks crossing the loft, onto which longitudinal plants will be placed to create a walkway.