Butt Window Flashings

Alternative details that allow the cladding to terminate up to a flashing without over-flashing it, require accurate fitting to be weathertight. See Butt Window Flashings
These details are known as butt flashings and can be used on flush or recess designs with a one-piece jamb. They are only suitable for areas with low or medium wind design loads, or in protected areas and require precise design, measurement, and manufacture to provide a weathertight solution.
Butt window flashings also require accurate installation to provide an aesthetically acceptable solution.
Butt flashings are not a preferred detail because they need extra timber for fixing and they should allow for drainage of a large catchment area.

The total amount of water draining from the catchment area of a multi-storey construction can be considerable, and butt flashings should dispose of it as a penetration. The catchment area is calculated by multiplying the width of the window opening by half the height.

Rain-water should discharge at a lap of the cladding, or if the building is not lined or has a cavity, it can be tracked to the outside via a double hemmed soaker flashing to discharge at the base of the building.

To slit the cladding and discharge a large volume of rainwater from butt flashings is not acceptable and, as it should be assumed that butt flashings will leak, provision should be made to drain the water to the outside. See Butt Window Flashings.


Wind Flashing (Butt Jamb)

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