Below new waterproofing
A cover board below a new membrane becomes part of the planned roof assembly. This can suit new construction or waterproofing replacement. Compatibility with insulation, adhesives and fixings needs to be checked; the board does not itself become a waterproof membrane.
Above an existing membrane
An exposed protective layer encounters weather, water, movement and maintenance. It must not obstruct drainage or access. Contact with the existing membrane and the proposed fixing method also require separate consideration.
Start with a section
Record the existing layer sequence: structure, vapour control layer, insulation, waterproofing and PV. Add known material names and thicknesses. Photos help with details, while old drawings should be checked against the actual condition. This turns a product question into a specific system question.
The correct position is a design decision, not a detail to resolve after purchasing.
Technical background: deu.sika.com ↗
A next step for your roof↗