Industrial sandwich-panel roof

A lightweight pitched roof for warehouses and logistics, made of self-supporting sandwich panels — two steel sheets enclosing an insulating core — laid on metal purlins. In a single prefabricated element it carries, insulates and weatherproofs: it is laid dry and fast over large areas, with the upper sheet profiled for water run-off and the laps sealed.

The sandwich roof panel is the evolution of the simple profiled sheet: between the profiled outer sheet and the flat inner sheet an insulating core (PIR polyurethane or rock wool) is foamed or bonded. The three parts work as one section, so a thin, light panel spans large distances between purlins with no intermediate supports.

Under load (snow, wind, maintenance) the upper sheet goes into compression and the lower into tension; without the core the two would slide and buckle at once. The core absorbs the shear and forces them to work together, generating enormous flexural stiffness for the weight. It is the same principle as a composite floor, on a lightweight scale.

The roof is pitched with a minimum fall: the outer sheet is profiled in tall ribs that channel the water, and the panels lap sideways with a tongue-and-groove joint, often gasketed. The continuous core gives the thermal insulation (very low U-values with PIR) and, in the rock-wool version, the fire resistance and acoustic insulation.

Panels are fixed to the purlins with self-drilling screws and sealing caps, in a number and pattern by calculation to resist the wind. The critical points are the fixings (through-holes to seal), the ridges, eaves and rooflights, and thermal movement: a dark sheet in the sun heats far more than the inner one, and the panel tends to bow — an effect to allow for on large formats.