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Building design drawings for masonry cavity wall construction generally attempt to contain most of the information needed to instruct the construction team on the types and placement of wall flashings. Some unique, low frequency conditions are often not described in detail in the drawings, and reliance is placed on the contractors to detail and install these unique flashing areas for watertight performance, using the concepts shown in the drawings for other areas. Frequently the resulting installation does not perform well, and leakage and disputes result. For example, the designer did not detail the trouble area fully or at all, and the contractor attempted to install using past experience or the available design information, yet the installation leaks. One such condition occured at the transition between a sloped roof ridge against the base of a higher masonry cavity wall, to a rake condition where the higher wall turns outward at an inside corner, as well as the rake condition itself. Another situation occured where a horizontal architectural feature penetrates a masonry veneer wall, bridging the cavity between veneer and backup wall, and is structurally secured into or through the backup wall.
Sometimes subcontractor trades do not realize or anticipate how their work interfaces with another trade. Masonry flashings that are possibly installed in a water-tight and well-performing manner can be damaged by other trades who do not realize the damage being caused, and the resulting combination leaks. One example is the manner in which window heads are sometimes anchored or fastened to the underside of steel shelf angles which support brick masonry veneer above.
This paper will discuss several examples of common leakage problems in masonry cavity wall construction, attributed to the above two concepts. The resolution of the problems, performed in recent case histories, will be presented, with suggestions for changes in original design drawings to help prevent the problems.
cavity walls, veneer, backup wall, dampproofing, throughwall flashings, sheet metal, sheet membranes, step flashings, roof ridges, rakes
Williamson & Associates, Inc., Atlanta, Georgia