Below the membrane: the cover board

Between insulation and membrane is the place for a thin, rigid cover board. It spreads point loads, gives the membrane a flat substrate and keeps the insulation out of direct contact with supports and tools. It lies dry, protected by the membrane, and is laid in the same working pass. That is only possible when the roof is open: on new build or a new membrane. That is the place of DEK.

On the membrane: the mineral layer

If the membrane stays in place, only the top is accessible. A site-applied mineral layer follows the membrane and cures into a firm surface. It sits in the weather, must bond to the actual membrane and must not impede drainage. Seams and support feet are detailed separately. That is the VLOEI route.

At the edge: the exposed board

Upstands, roof edges and penetrations stand vertically in the weather. Neither a cover board nor a liquid layer across the field fits there, but a weather-resistant mineral board, mechanically fixed and detailed to shed water. That is WEER. Before any choice, record the actual layer sequence: material names, thicknesses, fixing, condition of the seams. Old drawings show what was planned; photos and an opening-up show what is there.

The right position is a design decision at the start, not a detail for after the order.