Section 1503.2.1 Locations: Flashing shall be installed at wall and roof intersections, at gutters, wherever there is a change in roof slope or direction and around roof openings. Where flashing is of metal, the metal shall be corrosion resistant with a thickness of not less than 0.019 inch (0.483 mm) (No. 26 galvanized sheet.)

Code Interpretation

These codes imply that flashings are required at all transitions, walls, perimeter areas and at all roof penetrations. The code provides requirements for metal flashings - “the metal shall be corrosion resistant with a thickness of not less than 0.019 inch (0.483 mm)(No. 26 galvanized sheet.)” - however; it is the responsibility of the designer to provide proper flashing materials. It is a best practice to use the system manufacturer’s flashing materials for system compliance.

The flashing element is the most vulnerable part of any roof system because it is the point at which the horizontal roof deck and vertical surface join. It is also the intersection of two different materials, such as at parapet walls. Flashings are also vulnerable because they are applied around all roof penetrations such as skylights, HVAC units, vents, expansion joints and all other areas where membrane is interrupted or terminated. The primary purpose of the flashing element is to seal the membrane at all edges; a task that is difficult enough without bearing any design inadequacies.

The material selected should have an in-service life expectancy that meets or exceeds that of the membrane. This is an important characteristic because the flashing generally has to perform in more severe conditions than the membrane. The selection of inferior materials to save money up front generally results in severe economic losses due to premature failures.

If the flashing material specified does not conform to the roof system and surface that it is attached to, then even the most detailed flashing plans will fail. It is essential that this material is compatible with all adjoining materials and that it has the capability and durability to last the lifetime of the system.

The material must also have the ability to withstand all thermal and load induced movements. An allowance must be made for differential movement between the membrane and all other parts of the application. Base flashing should not be anchored to parapet walls, unless the parapet and the substrate are continuously connected and cannot expand or contract independently. Counter flashings should not be connected to base flashings unless the possibility of relative movement between them can be positively prevented. If the flashing material cannot sustain the strains of the roofing system movement, cracks and tears will develop and deteriorate the flashing.