The quality and service life of a roof covering made of zinc-titanium depends firstly on the design and execution of the roof structure as a whole and secondly on the zinc-titanium system itself. Where the roof is insulated, a system incorporating rear ventilation is the only method recommended by NedZink B.V. for roofs made of NedZink. If the roof is properly constructed, any corrosion of the zinc roofing materials caused by condensation water from the inside is virtually eliminated.
The construction principle is illustrated in fig. 1.
The components are identified beginning on the inside:
- Ceiling – any type, although it must be able to support the insulating material, or have the insulation attached to it.
- Damp control course made of metal or plastic film.
- Supporting rafters – generally made of wood.
- Insulation slabs, matting or foam between the rafters. It is even better if they can be made to run across under the rafters, although a different construction is required for this. The thickness of the insulating layer depends on the material used and the degree of insulation required.
- Ventilated cavity: thickness depends on pitch of roof (see table).
- Timber boarding: If Zinc-Titanium is to be used, the preferred type of timber is unplanned boards no less than 22 mm thick. There should be a 5 mm gap between the boards. If the roof pitch exceeds 45°, the substructure may be of boards with gaps of up to 10 cm. Nails must be countersunk to prevent contact with the zinc. Ideally, nails should be galvanized.
- NedZink the type selected for this type of roofing. The principal options are: the roll cap system, the standing seam system, the panel system (diagonal finish) and the NedZink System.
The ventilation cavity must be open to the external air via ventilation apertures at the lowest and highest points of the facade or roof. The air must be able to flow between apertures without major obstacles. The required dimensions for the gap and the apertures are detailed in the following table:
Min. cross-section of ventilation
apertures (top and bottom) per
m² of roof surface area
3° – 20°
Where a higher moisture level is present, as is the case with a temperature of 20° C and a relative humidity level of 60% (vapour pressure > Ps = 1400 Pa) the minimum pitch recommended is 7° .