VM ZINC® BASICS
Ventilation of VM ZINC® - Roofing and cladding
Contact with the outside air provides the CO2 required to form the natural patina of VM ZINC®.
Without the presence of outside air, VM ZINC® does not protect itself and if there is any condensation, a chemical reaction can occur. As a result there can be corrosion on the underside of the VM ZINC® which is not visible until holes appear on the outer skin.
Therefore, to ensure the durability of VM ZINC® fixed on roof boarding its underside must be ventilated.
The best ventilation is ensured by two continuous air inlets: one at the bottom and the other at the top of the roof slope or cladding.
For installation on roof boarding, the underside of the latter and thus the underside of the VM ZINC® will be ventilated. If it is impossible to realise this type of ventilation, it must be replaced by another air inlet system such as roof ventilators (slopes > 21°) or air vents. These air inlets are to be carefully spaced to ensure that the entire underside of the metal is ventilated.
Fixing fine mesh (<2 mm) to all the air inlets will deter insects, rodents and birds from entering.
The minimum depth of the air space under the roof boarding must be 40 mm. The total area of the air inlets (eaves and ridge) is 1/1,000th of the surface area of the roof, with a minimum width of 10 mm in the case of continuous ventilation.
In general we advise planning a total area for ventilation at the ridge that is 1.5 times greater than at the base of the roof. For slopes greater than 13 m long, intermediate air inlets should be planned for.
In most cases, a layer of insulating material is placed below the ventilated space. In order to avoid the risk of poorly installed insulation obstructing the air space, or of the insulation getting wet as the result of condensation, a breather membrane is required on the top side of the insulation. This breather membrane must be vapour permeable and end in the gutter, the box gutter or on the outside of the building.
This breather membrane can also prevent convection currents of (cold) outside air entering the building.
Given the increasing level of insulation in buildings, the installation of an effective vapour control layer on the warm side of the insulation is required.
The use of "PLUS" type VM ZINC® the underside of which has already been protected during production, means that installation can be done without ventilation of the underside (Natural VM ZINC® PLUS, QUARTZ-ZINC® PLUS or ANTHRA-ZINC® PLUS).
