Panel selection does not begin by looking at the catalogue. The catalogue shows fifty-six products, and all of them suit a building, but no two of them suit the same building at once. The choice is decided by the conditions of the building, not by the product: the regulation, the insulation target, the load to be carried, the humidity, the appearance and the lead time.
Six questions, asked in order, reduce the catalogue to a single line.
1. Which class does the fire regulation require?
This question comes first, because its answer constrains the other five. The class required at the permit stage decides the core directly.
| Core | Fire class (EN 13501-1) | Thermal conductivity |
|---|---|---|
| Rock wool | A2-s1-d0 | 0.045 W/mK |
| Hybrid | A2-s1-d0 | 0.045 W/mK |
| PIR | B-s1-d0 | 0.022 W/mK |
| PUR | B-s2-d0 | 0.022 W/mK |
| EPS | no published class | 0.038 W/mK |
If class A2 is mandatory, the decision ends here: a rock wool or hybrid core. The insulation target is then met with thickness, not by changing the core. Fire class and fire resistance are two different things: the class is the reaction of the material to fire (EN 13501-1), and resistance is the resistance of a building element in minutes (EN 13501-2). The test reports are in the Library section.
2. What is the target thermal transmittance?
The insulation expectation is written not as a sentence but as a U-value. In every heated or cooled space that number turns into a running cost.
A polyurethane core gives the same insulation at roughly half the section of rock wool; rock wool brings the fire class with it. The way to choose thickness and core together runs through the calculation: the U-value calculator gives the result for the section and the heat loss calculator its annual value.
3. What are the span and the load?
The purlin spacing, the snow load and the wind uplift decide the profile of the panel and the steel thickness. The number of ribs is not a matter of appearance but of capacity: a five-rib roof panel crosses a wider span than a three-rib panel of the same thickness. A seven-rib profile is a step above that.
The decision is read from the load table, not estimated. The tables stand product by product in the Library section.
4. Is the environment humid?
In cooled spaces and humid production environments, what decides is not the thickness but the continuity of the vapour barrier. A closed-cell core does not take water in; a rock wool core that gets wet loses its insulation value and never recovers it.
In buildings at risk of condensation, the joint detail enters the decision as much as the panel does: a joint left open takes away the gain expected from the whole section. The details are in the Library section.
5. How visible is the surface?
Where the elevation is on show, a concealed-fix panel is chosen; where it stays in the background, an exposed-fix system. On the coast and in aggressive atmospheres the coating class rises above polyester: PVDF or plastisol. That decision raises the initial cost and lengthens the interval between repainting.
6. Panel length and lead time
The standard range is produced in one piece up to 15.5 metres; a roof flow with no joints means both waterproofing and installation time. The EXO range is limited to 12 metres. The cover width is 1000 mm, and quantities follow from it: the panel area calculator gives the count surface by surface.
Writing the decision into the specification
The choice is written with values, not sentences. If these five lines are in the specification, there is no argument on site: core type, insulation thickness, fire class, steel thickness and coating, cover width and panel length.
Where there is no specification, the decision is made on site, and the decision on site is usually whatever is to hand. How to proceed on projects without a specification is the subject of a separate article.