Horizontal Metal Cladding

The weathertightness of horizontal cladding is entirely dependent on the flashings of cladding and penetrations, and because it is susceptible to the accumulation of condensation a cavity is required for all lined buildings.

It is recommended to seal horizontal laps with lap tape when they are enclosed in a cavity that is subject to condensation. This is needed to avoid the build up of moisture at the lap that can occur when dirt and condensation collect, which can increase the time of wetness and cause corrosion of the coated steel cladding.

All exposed horizontal metal flashings including the head or sill flashings must have a minimum pitch of 10° to avoid ponding and the build-up of dirt and debris. All hidden flashings must be durable for 50 years.
It is advisable to start the horizontal cladding at the window head level to provide a weathering the junction at this point. For this reason, it is advisable to make a horizontal break in multi-story construction to adjust the vertical module.

When the lap of the horizontal cladding does not coincide with the height of the penetration, it is necessary to slit the cladding to enable the fitting of 'under/over' flashings to allow water egress at head or sill flashings.

This method requires accuracy and skill to make a neat joint, at what is a vulnerable point, and which should be sealed to prevent water ingress. Because this joint relies solely on sealant and cannot be mechanically fixed, it is not a recommended option.

To avoid slitting the sheets where in a single storey building, a double hemmed jamb soaker flashing can be continued to ground level behind the cladding—providing there is provision to enable water to drain clear of the building. This is not a recommended option unless there is a cavity behind the cladding. Multi-storied buildings should have a sill at each floor level so that soaker flashings do not need to drain more than one level.


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