According to current regulations, the roof over heated rooms should have a U-value of no more than 0.15W/m2K.

In the sandwich panel industry, cores of EPS polystyrene, MWF mineral wool, PUR polyurethane and PIR polyisocyanurate are used between steel facings. Sandwich panels, as the panels are sometimes colloquially called, based on these cores are used both for building roofs and façades and for thermal insulation of existing walls and attics. Each of the aforementioned 'insulated sheet' cores is characterised by different thermal transmittance parameters, allowing the material to be optimally selected for the type of application:

1. Layered sheet' insulated with polystyrene EPS

Polystyrene has a low lambda of 0.040 W/m*K, which means that a 100mm thick EPS-based sandwich panel has a U=0.38 W/ m²*K. This is the thermal transmittance of 60mm PIR core panels. A 100 mm thick PIR core panel has a U-value of 0.22 W/ m²*K, i.e. a value like that of a sandwich panel with an EPS core of 175 mm.

This type of board is most often used to insulate small pavilions and office containers, storage buildings and also buildings where there are no fire resistance requirements. Given that EPS is used to insulate walls in traditional buildings, this type of application (sandwich panel with sheet metal on the outside, then an EPS core, and foil on the inside) is also relatively popular.

The advantage of 'sandwich sheet' insulated with EPS is the price. At thicknesses of less than 100mm, it can still compete cost-wise with polyurethane-based panels.

2. Layered sheet' insulated with mineral wool MWF

Mineral wool has similar thermal transmittance characteristics to polystyrene. Its advantage, however, is its high resistance to fire. Hence its frequent use as roof insulation. Due to fire safety requirements in some transmission and storage buildings (storage of flammable products, use of raw materials in production, work of many people in the hall, who must have enough time to leave the building during a fire), MWF core boards are increasingly being used to insulate not only the roof (the so-called sandwich or roof sandwich panel) but also the wall (similarly - also sandwich or wall sandwich panel).

Such a partition is capable of creating a firewall with a rating as high as EI 120, giving workers up to 120 minutes after a fire to leave the hall.

3. Insulated 'sandwich panel' with PUR core

Polyurethane, used in the manufacture of sandwich panels, has similar fire properties to polystyrene (NRO classification - non spread of fire), but at the same time has much better thermal insulation parameters, comparable to polyisocyanurate, which is higher in the hierarchy, also known as 2nd generation polyurethane. Due to its costs, which are similar to those of PIR, and its poorer fire protection properties, it is, like polystyrene, being used less and less frequently in investment projects. However, it is still relatively often used for spray insulation of roofs and ceilings.

4. Insulated 'sandwich panel' with PIR core

PIR-core board provides roofs and facades with high thermal performance as well as relatively high fire properties. With the right construction, the roof panels can achieve a fire resistance class of REI30, giving about 30 minutes to leave the building during a fire. In addition, the cooling slabs, thanks to their suitable construction, can provide a heat transfer coefficient as low as 0.10 W/ m²*K, which is significantly better than the high thermal insulation requirements due to come into force in 2021.

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