What a cover board should do

A cover board usually sits between insulation and roof waterproofing. It provides a suitable substrate and, in an appropriate assembly, can spread point loads. Compression, bending, fixing and moisture requirements matter alongside reaction-to-fire classification.

DensDeck Prime is a manufacturer reference using a modified gypsum core with glass mats. Its data sheet describes that material’s properties. [1]

VlamShield SHEET uses a cement-bound matrix with glass-fibre reinforcement: 10 mm nominal thickness and 10 kg/m². It is the mineral protective and load-spreading layer in our portfolio for installation between insulation and new waterproofing.

Gypsum-bound boards: consider the bound water

Gypsum contains chemically bound water. When heated, energy is needed to release this water. The statement that gypsum is fundamentally unsuitable because of a particular temperature is therefore too crude. What matters is the behaviour of the specific product in the tested build-up.

On site, dry storage, suitable fixing and the subsequent waterproofing count. A glass mat-faced roof board is not to be equated with any gypsum plasterboard for interior fit-out. Brand, product type and application must match.

Cement-bound exterior boards: robust material base, different weight

Cement-bound, glass-fibre-reinforced boards can be suitable for weather-exposed applications. A technical assessment documents outdoor conditions for the assessed board version. Thickness and density vary by version. The required board thickness follows from the task and the evidence, not from a blanket product comparison. [2]

WEER focuses on the mineral board above the roof waterproofing beneath PV and on supplementary edge details. There, water management, contact with the membrane and wind restraint are particularly important. An advantage outdoors is no proof that every such board may be loose-laid at will.

Thin composite layers: low build-up height, different stiffness

A very thin fibre-reinforced layer saves height and can be lighter. But it is not automatically an equally stiff load-distributing board. BarrierSheet, for example, states 2.5 mm and 3 kg/m²; the cement-bound approach of SHEET is considered in the same field of application beneath new waterproofing. [3]

For the comparison, heat transfer, joints and the entire tested build-up are important. One or two layers can lead to different load and cost packages. The analysis of thin composite boards explains these points.

Mineral wool, EPS and PIR are first of all insulation materials

Mineral wool brings a mineral fibre structure into the thermal insulation. EPS and PIR follow other material and insulation principles. Their properties influence fire development but do not replace consideration of the whole roof. Moreover, an insulation board is not an arbitrary alternative to a stiff cover board.

Instead of judging whole material families wholesale, compare the documented construction: insulation effect, compressive behaviour, fire side, waterproofing and fixing. The FRISSBE/ZAG guideline highlights the connection with PV geometry. [4]

For load spreading beneath new waterproofing, compare rigid cover boards. For exposure above the membrane, consider a suitable exterior board. For low build-up height, assess a thin composite and its stiffness separately.