Frequently asked questions & answers about sandwich panels (FAQ)

Sandwich panels are a durable and prefabricated building material with very good insulating properties that can be laid directly. The composite panels, which consist of two metal cover layers and an insulating core, are not only quick to install, they also generally have a high load-bearing capacity and high rigidity.

There are sandwich panels for the walls and sandwich panels for the roof. The panels have different thicknesses, usually ranging from 30mm to 240mm.

Roof panels have a trapezoid on the outer side, which serves to increase the load-bearing capacity of the panels. The thickness of the roof panels WITHOUT the trapezoid is called the core thickness. If the height of the trapezoid is also taken into account, this is referred to as the total thickness.

Sandwich panels consist of an outer shell and an inner shell, with a core of PIR (polyisocyanurate) or mineral wool in the centre.

Panels with a PIR core are classified as flame-retardant (B-s1,d0) in accordance with DIN EN 13501-1 Classification of construction products and building elements with regard to their fire behaviour.

Most panels made of rock wool are non-combustible and classified as A2-s1,d0 according to the EN 13501-1:2019 standard, which means that they do not contribute to the spread of fires, release very little smoke and do not produce burning droplets.

The outer and inner shells of the sandwich panels are made of 99% sheet steel, which is galvanised and coated. There are different thicknesses of coating and galvanisation. The sheet steel can generally be between 0.4 and 0.75 mm thick.

The outer and inner shells are coated in different colours. Common standard colours include RAL 7016, RAL 8012, RAL 9002, RAL 9006, RAL 9007, etc.

The shells usually have Eurobox lining, also known as light lining. Alternatively, the wall panels can be produced with micro-lining on the outer shell.

Sandwich panels have a wide range of uses, as installation is uncomplicated and time-saving.

Sandwich panels can be used in the construction of production halls or warehouses, but are also ideal for partition walls, tennis halls, office complexes, cold storage cells, paint booths, stables and shipbuilding.

Sandwich panels are also becoming increasingly popular in the private sector. Sandwich panels can be used to build a carport, but are also ideal for fences or garden sheds due to their ease of use.

In principle, a distinction is made between roof and wall panels. The structure of the panels is identical, except that roof panels have an additional trapezoid, which increases the stability of the panels.

Wall panels can also be produced with concealed fixings. With this variant, the fixing screws are not visible.

Another differentiation criterion is the filling of the panels. If the panels are primarily intended to achieve a high insulating effect, then a core made of PIR (polyisocyanurate) is an option. This rigid foam is characterised by high compressive strength and temperature resistance. It is a class B1 flame-retardant product.

If, on the other hand, there are fire protection requirements, then sandwich panels with a mineral wool (or rock wool) core are an option. These panels are ONLY recommended if the focus is really on fire protection. Otherwise, the disadvantages outweigh those of PIR foam. Rock wool panels are significantly heavier, considerably more expensive and insulate only half as well as PIR.

The weight of sandwich panels varies greatly and depends on the thickness of the outer and inner shell and whether it is a PIR core or a mineral wool core.

For example, the weight per m2 for a 40 mm PIR roof panel with 0.5 mm/0.4 mm shells is 10.9 kg, while a 150 mm roof panel of the same type weighs 15.1 kg/m2. In contrast, a 150mm roof panel with a rock wool core weighs
approx. 26 kg/m2.

The heat transfer coefficient (U-value) is a characteristic value for the thermal conductivity of a material. The lower the U-value, the better the thermal insulation of the component and the more energy-efficient the building.

There are also large differences in the U-values depending on the nature of the core.

A 100mm roof panel with a PIR core achieves a U-value of 0.22 W/m2.K, whereas a mineral wool panel achieves a U-value of just 0.38 W/m2.K.

This question cannot be answered without further information on certain parameters and should be checked by a structural engineer.

However, the span depends on the following factors: Thickness of the outer and inner shell of the panels, thickness of the core of the panels, snow load as well as wind load of the place where the building is located, roof pitch of the building. A structural engineer can use these values to determine the load-bearing capacity of the panels.

Above all, the snow and wind loads determined at the construction site, the core thickness of the panels and also the thickness of the inner and outer shells have an influence on the load-bearing capacity of the panels.

Flashings or end plates

The following accessories are required to properly finish a roof or wall with sandwich panels. Flashings or end plates enable a clean, watertight and visually perfect finish to the panels. There are different flashings that are used depending on the type of building and its location. The most common flashings used to finish a roof include ridge flashings, verge flashings, wind deflectors and eaves flashings. External and internal corners, U-profiles and drip mouldings are often used for walls.

Sealing tapes and profile fillers

Sealing tapes are used to prevent thermal bridges between the building substructure and the outer shell. Multifunctional tapes are also used to seal the connection joints of windows and doors against air and driving rain. Profile fillers are used to seal the gaps, e.g. between sheet metal and ridge or sheet metal and eaves. They prevent water pressing up, e.g. under the ridge sheet, or sloshing water in the gutter under the trapezoidal sheet. In addition, leaves, other flying objects and vermin are kept away or prevented from entering.

Screws and spherical caps

The screws to be used depend on the substructure and the thickness of the panels.

For outdoor use, stainless steel or bi-metal screws should always be used, preferably those that are self-drilling. For screwing the roof, it is recommended to use a 16 mm sealing washer and a spherical cap so that the pressure of the fastening screws is evenly distributed over the surface of the sandwich panels.

It is possible to install a PV system on sandwich panels, and there are various options for doing so:

The safest option is to anchor the PV system directly to the substructure using solar fasteners (hanger bolts); here the loads are transferred directly to the substructure and the panel is not subjected to any additional load. This variant is particularly suitable for small systems or in the private sector.

There are various mounting systems for commercial applications or large PV systems. A static calculation is essential for these systems, as the loads are transferred via the panel and without precise planning, the panel may be overloaded, resulting in irreparable damage.

For large-area PV systems, it is advisable to choose a higher coating, as the PV system constantly shades the surface of the panels, which prevents moisture from drying quickly. This can shorten the durability of the coating.