Knowledge

Flashing

Function & Code Requirements

Flashings are membranes that collect water that has penetrated the exterior wythe and direct it back to the exterior. Design cavity flashing above any horizontal element that will block the downward flow of water. The 2006 International Building Code requires flashing as follows: “Flashing shall be installed at the perimeters of exterior door and window assemblies, penetrations and terminations of exterior wall assemblies, exterior wall intersections with roofs, chimneys, porches, decks, balconies and similar projections and at built-up gutters and similar locations where moisture could enter the wall.”

Flashing Types

Flashing materials include but are not limited to sheet metal (copper, galvanized steel, stainless steel, aluminum, lead), EPDM (ethylene propylene diene monomer rubber), plastics and asphalt impregnated membranes. Self-adhesive membranes are popular with many masonry designers and provide adequate durability for many applications. Copper, stainless steel, and lead flashing are used in buildings where the designed service life is measured in hundreds of years.

Installation

Flashings must be installed in continuous runs with sufficient overlap and adhesive at joints to prevent moisture from migrating under the flashing.

Termination at Backup

Several methods are available for terminating the flashing at backup: 1) adhering to the back up with mastic or similar adhesive. 2) securing with a mechanically anchored termination bar. 3) inserting into a cut reglet in the back up wall. 4) wrapping through a mortar bed joint in the backup.

Termination at Exterior

As per the BIA (Brick Industry Association), the flashing should slope towards the exterior and extend beyond the face of the wall ½" to form a drip.

Flashing

Flashing End Dams

End dams are used to terminate horizontal flashing runs to contain water on the flashing where it will be directed out of the wall system via weeps. Where the flashing is not continuous, such as over and under openings in the wall, the ends of the flashing should be extended beyond the jamb lines on both sides and should be turned up into the head joint several inches at each end to form a dam.

Flashing

Flashing Laps, Flashing Corners

Flashing must be continuous to work properly. As flashing is not usually installed in continuous sheets, flashing should be lapped at least 6-in. and the laps sealed with a compatible adhesive. Fold flashing at corners or use prefabricated corner elements, sealed to the flashing at each side of the corner.

Flashing