Each separate envelope trade contractor’s work, regardless of its being thought of as a waterproofing system or not (e.g., exterior mechanical apparatus), must become part of a totally watertight building envelope. Equally important, all individual envelope systems must be adequately transitioned into other components or provided with watertight terminations. Often the tradesworkers completing this work are not aware of, trained in, or supervised in enveloping a building properly. And this is the number one cause of water infiltration in all types of structures.

The resulting improper attention to details is responsible for countless problems in construction. Properly detailing a building’s envelope presents an enormous task. From inception to installation, numerous obstacles occur. Highlighting this interrelationship of various envelope systems is the most important principle of waterproofing:

The 90%/1% principle: 90 percent of all water intrusion problems occur within 1 percent of the total building or structure exterior surface area.

This 1 percent of a building’s exterior skin area contains the termination and transition detailing, as discussed previously with Fig. 1.9. This 1 percent area all too frequently leads to breaches and complete failure of the effectiveness of the building envelope and is the main cause of all waterproofing problems.

Industry members, including contractors, designers, and manufacturers, now are recognizing the importance of the 90%/1% principle first introduce by the author. Architects must recognize the importance of these termination and transition detailing, manufacturers must provide the appropriate details with their specifications, and general contractors must provide the coordination and oversight of the numerous subcontractors involved in a single envelope for the completed product to perform as expected.

The 90%/1% principle is the reason that despite continuing technological advances, waterproofing continues to be one of the major causes of legal claims in the design and construction profession. It is not the actual manufactured waterproofing systems or envelope components that leak but the field construction details involving terminations and transitions.

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