The NZ Metal Roof and Wall Cladding Code of Practice is a comprehensive design & installation guide, and a recognised related document for Acceptable Solution E2/AS1 of the NZ Building Code.
To ensure the edge of the flashing does not mechanically remove protective coatings on the cladding, there must be enough clearance between the edge of a vertical flashing, or a notched flashing, and the cladding. Similarly, the edges of cladding running parallel to flashings, such as at a window head, should have clearance to avoid mechanical damage and allow drainage.
Having the lower edges of flashings apart from the surface they are covering helps to improve the cut edge durability of the flashing. Kick-out barge details are preferred to bird’s beak barge details for the same reason. The size of the clearance is not critical, but typically it is more than 5 mm.
Clearance is also necessary between the bottom of profiled metal cladding and large flat surfaces — a minimum of 25 mm clearance at a garage door opening and 35 mm for sheltered areas or cladding abutting a deck. Elsewhere the minimum clearance to the ground is 75 mm for unlined buildings and 100 mm for lined buildings and dwellings.
Above unpaved ground, greater clearance may be required to achieve durability depending on the roughness of the surface and the degree of vegetation control and soil levels. A minimum of 100 mm clearance is recommended for stone chip, 150 mm for a kept lawn and 175 mm for pasture. However, the effectiveness of these clearances is subject to the occupant ensuring that vegetation, debris, and soil do not build up against the cladding surface.
Greater clearance is necessary where gardens abut a wall, where lawn grasses are not grazed or maintained, or where soil spillage from adjacent banks may occur. Future landscaping effects on ground levels must also be considered.
The separation of profiled metal claddings from corrosive surfaces such as wet timber or concrete is more critical at the lower end of cladding, where high humidity levels may be experienced for extended periods.