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 required between the bottom of profiled metal cladding and large flat surfaces. For timber-framed dwellings, E2/AS1 requires a clearance of 35 mm to an adjacent roof, 100 mm to paved ground, and 175 mm to unpaved ground.
The clearance requirements for unlined buildings are less than that required for lined buildings, as the absence of lining enables the inner face of the cladding to dry more rapidly, and inspection and maintenance of the framing can be practically achieved.
Minimum Design Ground Clearance for Profiled Metal Cladding on Lined Buildings of Importance Level 2.
Ground Type
Minimum Clearance
Garage door opening
25 mm
Walls under canopies
35 mm
Paved
100 mm
Unpaved gravel
125 mm
Unpaved lawn
150 mm
Unpaved pasture
175 mm
Importance level 1 buildings may have a lesser clearance provided occupant maintenance prevents the build-up of debris against the cladding.
Greater clearance may be required 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 effectiveness of clearances in achieving durability requirements is subject to the occupant ensuring that vegetation, debris, and soil do not build up against the cladding surface. Design clearance from a surface is no guarantee of durability as effective clearances are subject to site development, occupant behaviour and building maintenance.
Vegetation or earth in contact with the cladding will increase the time of wetness and may contain corrosive compounds.
The separation of profiled metal claddings from corrosive surfaces such as wet timber or concrete is more critical at the bottom end of cladding, where high humidity levels may be experienced for extended periods. This may take the form of a 3 to 6 mm gap, an inert self-adhesive tape or a PVC vermin strip.
Internal environments are also important, ventilation must be adequate for the building use, and absorptive of corrosive substances must not be in prolonged contact with the external or internal face of the cladding or structure.
