Guest Blog – How to insulate a concrete floor

In this guest blog Kingspan explain different methods 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.

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