Stories From the Field

Post: Flashing or Through-Wall Flashing

Saturday May 5, 2012

Flashing or Through-Wall Flashing is a waterproof membrane used to stop moisture from penetrating porous masonry or to re-direct water out of a masonry wall. High quality flashings are composed of copper, lead-coated asphalt or other durable materials which do not degrade from long-term exposure to moisture or ultraviolet rays. When installed properly, flashings should extend the full width of the wall (or beyond) and are often paired with stainless steel drip edges.


AAA-1 Masonry & Tuckpointing was called out to a Lincoln Park residence to determine how water was infiltrating the dwelling. After removing the parapet wall capstones we discovered that the builder had used an inexpensive plastic membrane—the black material laid across the top of the wall—and had failed to size it correctly (refer to photo at left). Membranes must extend the full width of the wall in order to function properly, and here the flashings stopped a good two inches inside the walls rendering it completely ineffective. After disposing of the inappropriate flashing and allowing the wall cavity to dry out, we installed the correct flashing detail and re-set the capstones.

In this photo, AAA-1 Masonry & Tuckpointing is in the process of replacing a severely deflected third-story window lintel in a loft building in downtown Chicago. To the horizontal leg of the new window lintel we secured stainless steel drip edges in a continuous bed of caulk, and installed self-adhering Grace "Perm-A-Barrier" through-wall flashing and fastened it to the brick back-up wall using termination bars, masonry screws and caulk. On the right end of the masonry opening, we are in the process of installing a field-constructed end dam designed to prevent water from migrating into the masonry jamb. (Note how the glass window has been protected with Visqueen and painter's tape.)


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