Details of Masonry Walls

Flashing and weep holes:

A flashing is a continuous sheet of impervious material that is used as a barrier against the passage of water, into the building – Weep holes drain water from the cavity to the exterior.

External flashings:

Used to prevent moisture from penetrating the roof edge to wet the masonry wall, at the intersection of roof and the parapet wall – Uses a base flashing and counter flashing to achieve the purpose – Roof membrane becomes the base flashing; counter flashing comes from the outer wall to cover the base flashing – Should be turned in 8” into the wall to prevent water penetration.

Internal flashings:

Used to catch the water that has penetrated the outer wall and to drain it through weep holes to the exterior – Internal flashings should be placed at the bottom of the wall cavity and at every location where the cavity is interrupted; at heads of windows and doors, at window sills, at shelf  angles, and over exposed spandrel beams – Should be accompanied by a weep hole – Should be turned up 6” to 8” at the interior face of the wall and penetrate at least 2” into the back up wythe – Outside the wall, flashing should be carried at least 3/4” beyond the outside face and turned down at 45o angle.

Weep holes:

It should be placed at every 24” c/c horizontally – Min. diameter for a weep hole is 1/4” – Made  by inserting a short of rope laid in the mortar joint and later pulled out – Plastic tube and metal accessories should be provided to prevent insects from entering the cavity.

Material for flashing:

Made of sheet metal, UV resistant plastics, elastomeric compounds, or composite materials – Galvanized steel is unsuitable but stainless steel and copper are suitable; aluminum and lead are unsuitable.


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