Roof panel thickness: which design checks come first?

Don’t reduce the decision to the energy bill alone. Moisture processes, fire requirements and equipment also influence the roof design. In some buildings, cleaning conditions or coating resistance are important. The core thickness is selected as part of the whole solution, together with the type of facings and the method of forming the joints.

When choosing ready-made panels, compare their declared U-values for the specified variants. A lower value means less heat flow under the assumed conditions. The thermal conductivity of the core alone helps to understand the material, but does not describe the whole panel and its joints.

In one roof PIR panel family, a thickness of 100 mm corresponds to a Uc of approximately 0.21 W/(m²·K). Another 100 mm panel may have a different value. If the project requires better insulation, choose the variant that meets the target and check the other conditions. A popular thickness should not be regarded as automatically suitable for every building.

The calculation for the entire roof slope also takes thermal bridges into account. The junction with the wall, fixings and the skylight frame can worsen the result. Insulation selection should therefore cover the connection points, not just the central field of the panel.

To verify load-bearing capacity, the spacing and width of the supports and the type of loads are required. The tables refer to a specific core and thickness of both steel sheets. It also matters whether the panel acts on one or several spans. A result from a different arrangement is not interchangeable.

When modernising, inspect the existing structure and connections. The additional weight of the roof, installations or equipment must be included in the assessment. A greater core thickness alone does not solve the problem of a weak purlin. Reinforcement or a change in support spacing may be necessary. It is worth knowing these costs before approving the material.

Check the roof height at the parapet, window and existing wall. A thicker panel changes the position of the top surface. It may require different flashings, longer fasteners or adjustment of the gutter. This applies especially to extensions built under a former eaves overhang.

Also determine the locations of service penetrations. Openings and heavy equipment may need separate frames. Plan continuity of insulation and airtightness at each such detail. A well-chosen panel will not compensate for a gap in the insulation or a leaky joint with the adjacent building element.

When both versions meet the requirements, compare the cost of the entire roof. A thicker panel may change the weight of the element and the installation method. Sometimes it also affects the availability of lengths or production lead times. The difference is not always limited to the surcharge per square metre.

If one version requires reworking the flashings, include this in the total. A comparison of panel prices alone may reverse the result.

Prepare the final panel specification and a schedule of lengths. It should include the core type, its thickness, both facings, coatings and colour. Attach the required properties and the approved support layout. This will allow the replacement proposal to be assessed before delivery.

Take the final measurement after the structure has been prepared. Confirm the lifting method and access to the installation location. If the works have several stages, agree the compatibility of successive batches and the method of forming the joint. The selection is complete only when the correct panel suits both the design and the actual site conditions.