viqueen-floor-screedNWFS are specialists in the installation of damp proof membranes.

The installation of the damp proof membrane is a key stage of the building process, and one which really needs to be handled with care and attention to detail. Any faults with the installation, leading to damp ingress at a later stage, can be very expensive and difficult to fix.

NWFS only recommends the use of high quality damp proof membranes that meet British Standards. It is simply not worth the risk of using lower grade product for this essential function.


NWFS can supply and install many ranges of floor insulation from the list below ranging from a basic economy board to a premium product.

  • Polystyrene EPS (expanded polystyrene), e.g. Jablite
  • Foil-faced high performance rigid polyisocyanurate (PIR), e.g. Celotex GA4000, Kingspan TF70
  • Fibre-free rigid thermostat phenolic core for better thermal conductivity, e.g. Celotex FR4000, Kingspan Kooltherm K3
  • Specific insulation for underfloor heating applications, e.g. Celotex FF4000
  • Rigid extruded polystyrene insulation is recommended for specialist applications such as heavy duty flooring or heavily trafficked areas.

Tips on how to install your insulation successfully below a floor screed

  • Concrete slabs should be allowed to dry out fully prior to the installation of the insulation
  • The surface of the slab should be smooth, flat and free from projections. Beam and block floors should be level and grouted. Rough cast slabs should be levelled using a thin sand blinding to ensure boards are continuously supported.
  • The damp proof membrane (minimum 300 micron / 1200 gauge polythene) should be laid with joints well lapped and folded, to prevent the passage of ground water, over the concrete floor slab, or beam and block floor prior to laying the insulation boards.
  • The membrane should be brought up the surrounding foundation walls until it is sufficiently above the height of the wall DPC so that it will connect with or form the DPC.
  • The insulation boards should always be loose–laid with offset edges and joints lightly butted.
  • A strip of the insulation board (minimum 20 mm thick) should be placed vertically around the external perimeter of the floor slab in order to prevent cold bridging. The top of the strip of insulation board should be level with the top of the floor screed and the bottom should be level with the bottom of the horizontal floor insulation, and closely butted up to it.
  • Insulation boards should be overlaid with a polythene sheet (not less than 125 micron / 500 gauge), to prevent the wet screed penetrating the joints between the boards, and to act as a vapour control layer. Ensure the polythene sheet has 150 mm overlaps, taped at the joints, and is turned up 100 mm at the walls.