How to choose roof sandwich panels: key selection criteria

Roof sandwich panels are used as lightweight roofing for industrial halls, warehouses, retail buildings, cold stores and agricultural facilities. A single panel combines external steel facings with a thermal-insulation core, allowing it to serve as roof covering, thermal insulation and an element transferring loads to the supporting structure.

Panel thickness or price alone should not determine the choice. The core type, support spacing, snow and wind loads, roof pitch, fire-safety requirements and internal building conditions must also be checked. Only by considering all these factors can a suitable solution be selected for a particular project.

Which core should be chosen for a roof sandwich panel?

The core primarily determines thermal performance, but it also affects panel weight, behaviour in fire, acoustic properties and structural capabilities. PUR, PIR and mineral-wool cores are most commonly used in roof sandwich panels.

PUR and PIR roof sandwich panels

Panels with a polyurethane PUR or polyisocyanurate PIR core provide very good thermal insulation at relatively low thickness and weight. They are therefore frequently used on halls, warehouses, retail buildings, cold stores and agricultural facilities.

PIR has a different chemical structure from PUR and generally performs better when exposed to fire. However, the core type alone does not determine the fire safety of the complete roof. The declared performance of the specific panel and the requirements applicable to the proposed building must be checked.

Mineral-wool roof sandwich panels

Roof sandwich panels with a mineral-wool core are primarily used in buildings where fire protection or acoustic insulation is particularly important. They are heavier than PUR and PIR panels, so their use must be considered when designing the roof structure and planning transport and installation.

The choice between PIR and mineral wool should be based on the design, intended use of the building and required performance, rather than on a single material property.

How should roof sandwich panel thickness be selected?

Panel thickness primarily affects the thermal performance of the building envelope. An unheated warehouse, a heated production hall and a cold store or temperature-controlled facility will each have different requirements.

The following should be considered:

• the building’s purpose and use,
• the required indoor temperature,
• roof thermal-performance requirements,
• the core type and its declared properties,
• the risk of water-vapour condensation,
• the requirements of the building design.

There is no single thickness suitable for every building. Comparing sandwich panels by thickness can support initial product selection, but the final choice should be based on the required thermal and structural parameters.

Does panel thickness determine load-bearing capacity?

Thickness matters, but it is not the only parameter determining permissible support spacing. Load-bearing capacity also depends on the facing profile, sheet thickness, core type, support arrangement and loads acting on the roof.

Before ordering, consult the manufacturer’s load-span tables for the specific panel. Compare them with the snow and wind loads for the building location and with the structural layout and spacing of the steel purlins.

Photovoltaic systems, ventilation equipment, rooflights and other technical elements create additional loads. Their weight and fixing points should be included in the structural design rather than assessed solely from the panel’s general load capacity.

Why is roof-panel profiling important?

The outer facing has a pronounced profile that increases stiffness and helps drain water from the roof. Designations such as G3 or G5 may refer to the number of main ribs or a particular profile variant, but naming conventions differ between manufacturers.

Selection should therefore not be based on the profile name alone. Cover width, joint geometry, load capacity and the availability of matching system components must be compared. These include fasteners, seals and flashings for sandwich panels.

Roof pitch, watertightness and panel length

The minimum roof pitch depends on the system, panel length, transverse joints and additional roof elements. It must always be verified in the manufacturer’s technical documentation and the building design.

Watertightness depends mainly on:

• correct alignment and engagement of panel joints,
• appropriate seals,
• properly executed transverse joints,
• correct fastener positioning and tightening,
• careful ridge, eaves and edge flashings,
• effective drainage.

Long panels reduce the number of transverse joints but make transport, unloading and installation more difficult. Their length should reflect roof dimensions, transport restrictions and the lifting method.

How should the external and internal facing coatings be selected?

A standard coating may be sufficient in typical dry interiors. Agricultural buildings, processing plants, wash bays and buildings with high humidity or aggressive atmospheres may require facings with enhanced corrosion resistance.

Conditions on both sides of the panel must be assessed. The external facing is exposed to UV radiation, precipitation and temperature changes, while the internal facing may come into contact with moisture, chemicals or substances generated during building operation.

Common mistakes when choosing roof panels

• selecting solely by price or thickness,
• ignoring load-span tables and support spacing,
• using a coating unsuitable for the internal environment,
• failing to account for rooftop equipment,
• ordering without checking transport and installation feasibility,
• using unsuitable fasteners, seals or flashings,
• allowing breaks in insulation or leaks at joints.

What information is needed to prepare a suitable solution?

• the building’s intended use and location,
• roof dimensions and pitch,
• support or purlin spacing,
• required indoor temperature,
• thermal and fire-performance requirements,
• humidity and corrosivity conditions,
• details of rooflights, photovoltaics and rooftop equipment,
• the planned installation date and method.

e-PROJECT21 supplies PUR and PIR roof sandwich panels, mineral-wool panels and the components required for a complete roof system. For larger projects, material selection can be combined with sandwich-panel hall design or sandwich-panel installation.

The final structural solution, support spacing and fixing method must comply with the building design, the manufacturer’s documentation and the requirements applicable to the building.