Solid floor insulation – How to create a solid, insulated floor

Here, using some simple 3d models, we look at how to create a solid, insulated, ground floor without the use of a concrete slab.

If you’re looking for suspended floor insulation, please go to our page on suspended floor insulation here. Otherwise, read on…..

The floor build-up

(click on the models to allow 3D viewing, full screen icon bottom right)

This build-up can be used to replace a standard solid floor construction using a concrete slab and PIR insulation and creates a free draining, re-useable floor structure that is completely dry and can be finished immediately. This makes it ideal for projects where time is of the essence or where lots of timber is present that needs to be kept dry.

The actual specification for the floor build-up would be as follows:-

Floor finish
45mm Lithotherm underfloor heating tiles
22-35mm BeltermoTop wood fibre boards or UdiTOP wood fibre boards
Ampatex Solero weather resistant vapour control layer membrane, (all joints taped with Ampacoll Flexx Pro airtightness tape)
10 – 30mm levelling layer of Cemwood CW2000 insulating levelling aggregate
Geotextile membrane
250mm (compacted thickness) Foamglas Aggregate (Such as Geocell)
Geotextile membrane

So, on to the installation, starting with the Foamglas aggregate. This is installed to the required thickness to achieve the building control target, typically between 200 – 250mm (contact us for a definitive specification). The Foamglas is installed in 2 layers over the geotextile, raked level and compacted with a plate compactor to ensure solidity. It is difficult to get this perfectly level so, once the perimeter insulation has been installed we recommend using a layer of geotextile membrane over the top and a layer of the Cemwood CW2000 to level the surface exactly. The Cemwood layer should be screeded/scraped across the top of the membrane, using rails as a guide.

The Ampatex Solero vapour control/airtightness/moisture barrier membrane is then installed in sections over the Cemwood layer, with all of the joints well taped and an upstand around the perimeter to allow connection to the walls or IWI system that may be used. It is important that this layer is not punctured as it is the airtightness layer for the floor.

The wood fibre sarking boards are laid over this in strips to allow you to walk over the floor build-up and install the membrane. Do not walk directly on the cemwood. These boards form a flat, clean base for the Lithotherm underfloor heating tiles and also provide the additional benefit of absorbing sound from the tiles, making the floor much better at absorbing impact vibration.

Once the wood fibre boards are in place the Lithotherm tiles can be laid and the pipes installed using the following procedure:-

  • Starting with a full tile placed 100-120mm away from the wall perpendicular to the grooves and abutting the perimeter insulation on the edge parallel to the grooves, lay the Lithotherm tiles in rows with the tiles firmly butted up to each adjacent tile.
  • The second row should start with a half tile, connecting the T&G connection with the row adjacent to it,  to create a brick bond pattern. Generally the rows should proceed across the floor in such a way that space is left to be able to install the last 5-6 rows , one tile at a time in a diagonal line, to prevent the installer having to walk on the tiles.
  • Rows should be finished in such a way that the brick bond pattern is maintained and the 100-120mm gap is left against the wall perpendicular to the grooves.
  • The tiles should not be walked on during installation, except by the installer and only when necessary. Lay boards over the tiles to prevent damage if access is required.
  • Once complete, the pipes can be installed in loops of around 100m (roughly equivalent to 10m2 of tiles). The pipe should run from the flow side of the manifold to the tiles and be laid in every 4th groove, starting with the first. Pipes can be bent by hand at the end of each run.
  • Once the 50m point is reached on the pipe (identified by the length markings on the sidewall of the pipe) then the pipe should return in between the first set of pipes laid, at the same spacing, so that once complete every second groove is filled.
  • Once all the pipework is installed and pressure tested fill the voids around the perimeter of the tiles, including the pipework, with a dry-mix cement screed, flush with the surface of the tiles.
  • Lay Lithotherm reinforcing mesh over the entire surface of the floor and bond to the surface of the tiles with a 3mm layer of flexible tile adhesive. Any adhesive conforming to BS EN 12004 C2TE is suitable. Ensure 100mm laps on the mesh at all joints.
  • UFH system must be off and at ambient internal temperature  during laying of mesh and adhesive to allow correct curing of the adhesive.
  • Once cured in line with the adhesive manufacturers guidance the surface is suitable for receiving tiles as per tile manufacturers guidance.

For more information on installation please contact us or see the online installation guide at

How does this fit in with the rest of the building?

(click on the models to allow 3D viewing)

Here you can see how the suspended floor insulation joins up with the internal wall insulation, how it goes through the first floor and how it meets the roof or ceiling insulation. Obviously the floor buildup above is solid but the Ampatex Solero membrane will still be bonded to the surface of the wood fibre insulation in the walls as shown.

If you have any questions about this installation, please contact us.

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  1. Hi could would you please advise on internal board for a cavity filled wall. The cavity is filled permabead. we would like a breathable product for our outside, facing internal wall. We have taken them back to the internal brick and breezeblock wall.

    Thank you for your help and advice.
    Kind regards Amanda

    • Hi Amanda

      We wouldn’t usually suggest insulating the inside of a cavity filled wall as this can exacerbate moisture issues within the wall. However, if you do not have any timber bedded in the wall you could line the interior with the UdiIN2CM board. This would improve the comfort levels on the inside of the wall by insulating you from the masonry and raising surface temperatures.

      Hope that helps but please contact us for any further advice.