Water management affects the overall durability and performance of our structures. Through wall flashing is abovegrade water management for waterproofing. It is located at and along the bottom of each wall section in an exterior wall assembly where it diverts water through dedicated outlets to the face of the exterior finish. The flashing is closed with end dams at discontinuous sections.
As a component of the overall water management of a wall system, the through wall flashings' components will interface with other parts and component systems in the wall assembly. So it is important to understand the function and interface of those surrounding materials and component systems to achieve the overall water management goal.
Through wall flashing an arched masonry assembly at and along the top of a non-flanged window, door, or fixture will follow the same principles and installation sequencing as found in through wall flashing masonry above the straight head of a fixture. (The head of a fixture in a wall assembly is the bottom of the wall section above a fixture.)
The component installation sequence is: steel angle, drip edge (International Building Code 2009 1405.4, Flashing; “protecting flange” means a projecting drip edge) adhesive-backed membrane flashing, end dams, weeps, and depending on the wall type, either mechanically fastening (with a termination bar) and sealing (with an approved mastic or sealant) the uppermost edge of the flashing or, sealing only the uppermost edge of the flashing.
The deciding factor for whether or not to use a termination bar will be the wall type: non-cavity wall or cavity wall. In a non-cavity wall, grout or mortar fill behind the veneer will physically restrain the membrane flashing and its uppermost edge. In a cavity wall, a termination bar will be necessary to hold the top edge of the membrane flashing in place over the life of the wall assembly.
In masonry, the arched head of a non-flanged fixture will either be detailed with a steel angle, formed to the shape of the arch, or be detailed without one. When the detail includes a steel angle, the exterior extending leg of the steel angle provides support for the drip and adhesive-backed membrane flashing.
The position of the exterior extending leg of the steel angle, in relationship to the fixture head frame, also establishes a space for placing a backing rod and sealant. The sealant is the exterior finish in this part of the wall assembly. It stops the elements at the fixture-to-wall interface, so it is an important and integral part of the overall protection.
Masonry detailing above arched non-flanged fixture heads that does not call for a steel angle must be supported by a falsework or removable form of some type. In this condition, the key to successfully installing the drip and membrane components of the through wall flashing assembly will be devising a substitute for the steel angle, which will be described as a metal L flashing.
This L flashing serves as a drip and a support for the exterior extending leg of the adhesive-backed membrane flashing.
This flashing method will manage water at and along the wall above the fixture and manage air and water at the fixture frame's interface with the surrounding materials.
Maintenance of the sealant joint should be the only anticipated service issue over the life of this exterior wall assembly. Following these details will enable a sealant contractor to initially install the sealant in a space that is preferred by most sealant manufacturers and to remove and replace it after its service life has expired.
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The arched through wall flashing will be assembled in the following order: