Is the existing waterproofing worth retaining?

Start with condition, moisture, seams and connections. An additional protective layer does not repair wet insulation or defective terminations. If new waterproofing is already planned, the work can be combined. If the membrane remains intact, solutions above that level become attractive.

Document the actual assembly. Old drawings, product labels and professionally made inspection openings complement each other. The decision also needs information about PV supports and future repair access.

Membrane retained: WEER on the roof surface beneath PV

WEER addresses weather-exposed mineral boards above the existing waterproofing and beneath the PV installation. Project planning considers PVC-P, granule-surfaced bitumen, PIB and TPO/FPO. The specific combination determines whether an additional contact or separation layer is needed.

Drainage, wind restraint, board joints and membrane contact are designed together. The outdoor durability of a suitable board is an advantage here. Its supporting documentation is checked against the intended use and the manufacturer's conditions. [1]

New waterproofing: DEK or SHEET beneath the membrane

If the membrane is renewed or a technically suitable new roof assembly is installed, the position between insulation and waterproofing becomes available. DEK focuses on the stiffer cover board; SHEET on the thin fibre-reinforced mineral layer. Both approaches are selected according to their specific task.

Such work can often be combined more readily with planned roof refurbishment than with recently completed waterproofing. The comparison documents show the layer sequence, fixing, additional weight and extra installation work. [2]

An adapted surface: VLOEI and the substrate

A site-applied mineral compound can offer another route. VLOEI focuses on cement-bound material concepts and application with a squeegee or trowel. The work sequence includes substrate preparation, application and curing.

Adhesion, movement and moisture need to be assessed before selection. A trial area on the actual roof is particularly valuable. The comparison of coatings and boards shows how weather windows, labour and repairability differ.

Make the economic decision together

Compare options including PV removal, waterproofing, fixing, added loads and future maintenance. Limited spare capacity may restrict material weight; a tight programme may make drying times and weather allowances decisive.

The FRISSBE/ZAG guideline considers PV in the context of the roof. A specific retrofit brings together this system understanding, project requirements and the available evidence. The result is a reasoned recommendation rather than a universal product answer. [3]

With intact waterproofing, first compare options above the membrane. If reroofing is planned, include DEK or SHEET beneath the new membrane. Allow for PV removal and later repairs.