Thermal Insulation below Underfloor Heating

Why Conventional Underfloor Heating Systems Have an Insulation Layer and a Low Profile Underfloor Heating Normally Does Not Need This

The conventional construction of an underfloor heating system with a heated screed above the heating pipes normally also has a thermal insulation layer. Why is that?

The thickness of the heated screed and the insulation below the heating pipes are mutually dependent. The 50mm thick screed protects the insulation so that it is not indented by traffic loads. The heated screed builds up thermal resistance above the heating pipes impeding an efficient release of heat into the room. Therefore the insulation under the heating pipes must ensure that heat does not initially seep into the floor structure before it is able to reach the surface of the floor and enter the room.

In addition, the thick heated screed acts as a heat reservoir. What at first sounds good, often has drawbacks in practice. If sometime not very much heat is needed in the room, this heat reservoir gives off heat afterwards. If the underfloor heating is switched on after being off for a while, the heated screed lengthens the heating-up period and delays the release of heat into the room. The response time of the underfloor heating slows down.

Further drawbacks of conventional superstructures for underfloor heating: The insulation and heating screed normally have a structural height of 65 to 90mm. This structure imposes a considerable additional load of around 110 kg/m2 onto the existing ceiling. This procedure is often unsuitable for retrofitting underfloor heating in existing and older buildings.

The insulation of a storey ceiling can be neglected thermally, provided the rooms above and below the ceiling are heated. Insulation measures are required solely for noise prevention. The FLEXIRO thin-bed underfloor heating system utilises these insulation layers. If a thin-bed underfloor heating system is built onto an existing storey ceiling, the "thermal resistance" of all the materials built into the ceiling already acts as adequate insulation downwards. The thin heating pipes lie just below the surface of the floor and thus quickly emit heat into the room almost loss-free.

Moreover for comparable heat output, the heating water temperatures of the thin-bed underfloor heating system at around 35°C are much closer to the target room temperature than those of a conventional underfloor heating at around 45°C. This is also why the "heat loss" to the floor structure is far lower in the case of thin-bed underfloor heating. For these reasons, additional insulation under the thin-bed underfloor heating can normally be dispensed with.


Minimum Thermal Conduction Resistances of the Insulating Layer

The current (German) energy saving ordinance (EnEV) gives information about the obligation to insulate and the minimum values of thermal insulation to be adhered to for the top storey ceiling and the bottom storey ceiling above the cellar or ground. DIN EN 1264-4 for water-based surface embedded heating and cooling systems along with the energy saving ordinance regulate adherence to insulating values below underfloor heating systems. Here, the existing insulation in the floor or underlying intermediate ceilings can be included in the calculation of insulation values. Below are the specifications for the thermal conduction resistance under the different room conditions.



Heated room lying underneathUnheated or occasionally heated room lying underneath or room lying directly on the groundRoom lying underneath with external air temperature

Design external temperature Td >=0°C

Design external temperature 0°C<Td >=-5°C

Design external temperature -5°C>Td >=-15°C

Thermal conduction resistance (m2K)/W






Table from DIN EN 1264-4

If the Thermal Resistance of the Insulation Is Insufficient

In a modernization project, it can occasionally happen that the existing floor structure does not have the minimum thermal protection required for energy-saving operation of the thin-bed underfloor heating. This could be the case if an old stable building is to be converted into living space, or a room above an unheated cellar or a drive-through is to be modernized. Since it is not pleasant to stand on a cold floor even in summer, you should think about a complete overhaul of the floor structure in these cases.

The insulation of the low profile underfloor heating can be done here by doubling up. For this purpose, FLEXIRO offers load-bearing insulation panels in various thicknesses. The insulation panels are glued to the prepared old floor. The technical description of the installation of the insulation boards gives precise instructions on how to proceed. The FLEXIRO underfloor heating can be installed on the non-slip insulation panels using the knobbed mat laying method. After pouring a self-leveling leveling compound over the 10mm PE-RT heating pipes, the floor structure can be finished with tiles, laminate or vinyl.

The doubling method can also be used to compensate for height differences between rooms. If the uninsulated area is a cellar ceiling and the cellar is not heated, the insulation panels can also be installed on the cellar ceiling from the cellar.