If you are doing a ‘flat reform’, the typical Valencian builder will expect you to lower the ceiling with escayola (plaster), to make it easy to rewire the flat. However Escayola does nothing to insulate the flat from the cold / heat or from noise. Also you lose much more headroom with Escayola. The cost effective alternative is pladur (plasterboard), fitted with a layer of roofing felt between the old ceiling and the plasterboard. Insulation against temperature changes is important in top floor flats and on walls that get hit by the afternoon sun. Sound insulation is also important. In the main bedroom I recommend sound insulation in the ceiling and on the wall where your bed head will be. When contracting for ‘pladur’, make sure that the contractor puts in the best / thickest roofing felt. If you do not include painting in the contract, make sure that the installer prepares the board for paint. Ie applies tapes to the joints and filler to the holes left by the nails.