How to insulate a concrete floor

Insulating a concrete floor

There are a number of different ways of insulating a concrete floor. Much depends upon whether the floor is new or existing; how the floor will be used; the type of construction, and what you want to achieve.

There are a few things to consider to help make your decision easier…

Is the insulation strong enough?

If your concrete floor is for industrial or heavy duty applications, then any insulation you use needs to have a high compressive strength – to take the weight of whatever is above. Typically the insulation would be situated below the slab and below the damp proof membrane for heavy duty use, whilst normal domestic buildings would have a higher performing, lower compressive strength material above the slab.

How much space do you have?

How much space you have is important. For example, if you are digging down to lay a new slab, then you will need to leave room for the insulation. The thicker the insulation, means the more material you will have to excavate and dispose of. If, however, you are insulating on top of an existing slab, then you will need to consider things such as whether you need to replace or remove skirting boards, door jamb heights, ceiling heights etc. Once again, a thinner insulation such as vacuum insulation may be a more cost-effective or more practical option in the long run.

What u-value do you want to achieve?

You also need to work out what U-value you want to achieve. This is determined by the Perimeter / Area or P/A  ratio and soil type (the UK is predominantly clay. This soil type is taken into account should the soil type not be known, however some areas may be rock or sand in which case this will effect the thermal performance as they have a higher thermal conductivity when compared to clay, meaning more insulation would be required to achieve the same U-value). A whole separate blog exists on this subject, but basically it calculates how much of the floor perimeter is exposed to unheated or external spaces as a proportion of its total area. The more exposure (the high ratio), the more insulation is needed to achieve a particular U-value.Where do you want the insulation within the floor build-up?

This is a crucial question if you are considering using underfloor heating. Insulation directly under a thin screed or as part of a floating floor will mean that you will experience faster response times from that heating. If you are considering a ground source heat-pump with underfloor heating as the heat emitter, where the heat source is a continuous low trickle, then the insulation may be better under the slab as the concrete will act as  ‘thermal mass’ to release and regulate the temperature of the room above it. However if you require a quick heating response as well as thermal mass to help regulate the room temperatures then the underfloor heating should be placed within a screed with the insulation layer beneath the screed and above the floor slab.

A few products that may be of use that include edge and corner detailing are shown below…

Domestic Floor
Kingspan Optim-R Flooring System
Kingspan Kooltherm K3 Floorboard

Heavy duty flooring
Kingspan Styrozone

Floating floor
Kingspan Thermafloor TF70

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Kingspan Insulation is a market leading manufacturer of optimum, premium and high performance rigid insulation products and insulated systems for building fabric and building services applications.

0 comments on “How to insulate a concrete floor
  1. I have a bedroom over a cold garage. The garage ceiling is suspened .
    I would like to make the bedroom warmer in winter and cooler in summer. Would applying rigid insulation sheets to the ceiling of the garage be effective. ?

  2. I would like to insulate and put flooring down in my cellar. At this time it is uneven damp bricks + head room is limited. Would it be – levelling compound – membrane – 30mm insulation boards – 15mm ply – flooring.

  3. I am just about to install a new floor to my property. We have levelled in the duff. Do we put the damp membrane down before the kingspan and concrete or put the kingspan down, then the membrane and concrete? Thanks in advance.

    • Hi Neil,

      If you are considering using Kingspan Kooltherm K103 or Kingspan Thermafloor TF70 a DPM should be laid beneath the insulation to prevent the passage of ground water. A polythene separation layer should then be installed between the concrete and the insulation to prevent the wet concrete penetrating the joints between the boards and to act as a vapour control layer.

      If however you are considering using a Kingspan Styrozone product, the DPM can be laid above or below the insulation, please bear in mind however, if the DPM is laid directly onto the hardcore below the insulation, a polythene separation layer should be installed between the insulation and the concrete as above.

      Hope this helps.


  4. i have a conservatory base wall of approx 6mtrs wide by 3 mtrs depth. i have hardcore to a level. i dont think i have left a great deal of room for a minimum of 50mm therm block insulation.
    whats the worst that could happen if i failed to insulate the floor please


    • Hi Jeremy

      This will need to be discussed with your local building authority, as they are ultimately the ones that will sign off on any project. An uninsulated floor may reduce the thermal efficiency of the room in question.

  5. We have just bought a property and it has concrete flooring which requires insulating to help reduce the energy bills.Which is the best to use and can anyone lay it or does it require a specialist

    • Hi Sue,

      We would recommend the use of Kooltherm K103 Floorboard if the insulation being placed beneath screed, or Thermafloor TF70 if the insulation is being laid beneath a floating timber finish. Unfortunately we do not have a list of improved installers, however, general contractors with experience of laying floor insulation and DIY’ers should be able to install the product. Please ensure that either yourselves or the installers read the site work section of the product literature document beforehand. Advice can also be sought from our technical team, please call them on +44 (0)1544 387 382.

      Hope that helps,

  6. We’re in the process of planning the renovation of our bungalow 1968 bungalow – the majority of the flooring is suspended timber (which I’m confident I know what I’m doing with) but the property has been extended in two places (at different points in time) with a concrete floor – Is there any way of telling if this concrete floor is already insulated?

    • Hi Rich

      Unfortunately there would be no visible signs or indications if the floor is already insulated. The only way to tell would be to excavate part of the floor. Even then it would difficult to identify the insulation that may be there due to varying factors, such as the condition, the way the insulation was installed, whether or not there are visible manufacturer logos on the facings etc.

      Sorry we can’t be of more help in this instance.

  7. I have concrete slab with DPM underneath and up walls. When wooden floor/ its insulation layer and chipboard subfloor underneath that was removed, there was then a thick layer of compacted polystyrene balls followed by a moisture barrier. Now all this has gone…its made a huge difference to the height of the room. My question is: once the reno is underway and the moisture barrier relaid, can I lay a thinner insulation on top (rather than the large polystyrene layer) and then add the wood floor insulation and wooden flooring…thereby omitting a sub floor? If so..what product would be suitable? I did see Air-Cell but doesnt seem to be available in UK. Sorry its a bit long winded! Thanks.

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