Sheet Metal Failures

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By Mike Tonsbeek

Many building interior moisture intrusion issues are attributed to sheet metal failures. The primary cause for this condition is failed caulking joints. There are several reasons why these joints fail, such as inadequate attachment to the sheet metal components to adjoining surfaces such as walls, chimneys and other vertical or horizontal surfaces. Inadequate attachment relies on the caulking to keep these areas attached to each other or to surface they are mounted to, thus stressing the caulk beyond its limitations that it was intended to perform to.

Another reason that caulking joints fail is due to the application of the caulk itself. In many instances the sheet metal joints are surface sealed. This condition leaves the caulk exposed to the elements; this accelerates the deterioration of the caulk. Thermal expansion and contraction of sheet metal components and adjoining surfaces will also stress caulking beyond its limitation when only applied to the exterior surface of the joints.

For sheet metal components to perform in a satisfactory manner they must be properly lapped with caulk in between the joints, provided with proper attachment methods to the surfaces they are mounted to with acceptable interfacing to exterior cladding systems of the structure.

In some instances caulk must be applied in an exposed manner such when installing counter-flashing systems to masonry or structural concrete. With this type of application, the exposed caulking should be inspected periodically by a qualified waterproofing professional to make sure that caulking is performing as intended and to maintain the waterproofing integrity of the structure.