Wednesday, February 27, 2013


Considering that these two simple principles cover most leakage problems, it would seem that preventing water infiltration problems would be easy. Certainly, prevention of envelope failures must be a proactive process implemented before actual field construction activities commence. One of the first steps to implement this quality control process is to encourage preconstruction envelope meetings that include all subcontractors involved in the building envelope and cover the following topics:

● Review of the building facade components
● Review of the proposed waterproofing and roofing systems related to the building envelope
● Following the envelope barrier/drainage systems front line to ensure complete continuity
● Reviewing all transitions between envelope components to ensure effectiveness and compatibility
● Reviewing all termination details for waterproofing adequateness
● Instructing all attendees on the necessity of meeting the 90%/1% and 99% principles
● Assigning the responsibility for each termination and transition detail

The last issue is often the root of the 90%/1% principle, the fact that many leaks are directly attributable to transition details that are never installed because the general contractor overlooks assigning responsibility for this details in their subcontracts. For example, refer again to Fig. 1.9; whose responsibility would it be to install the reglet detail provided for the below-grade waterproofing-to-dampproofing transition? The general contractor might easily neglect assigning the completion of this detail to one of the involved subcontractors.

Since the waterproofing membrane would be installed first in most cases, it would be more appropriate for the dampproofing applicator to finish this detail. Although the masonry contractor as part of their contract often applies dampproofing, few masonry contractors understand the importance of this detail. What if the dampproofing used is a coal-tar-based product that is incompatible with the urethane waterproofing membrane? Further complicating the situation, an acrylic sealant might be used to finish the detail that is not compatible with either the membrane or the dampproofing.

 typical building envelope.
FIGURE 1.9 A typical building envelope.

 Such situations continually occur during field construction activities and result in facilitating the 90%/1% principle failures.

Unfortunately, all too often waterproofing is considered an isolated subcontracting requirement, and few architects, engineers, general contractors, and subcontractors understand the importance of knowing the requirements of successfully designing and constructing a watertight building envelope. It must be clearly recognized that all components of a building exterior facade, from the backfill soil selected to the mechanical rooftop equipment, are integral parts of the building envelope and that all are equally affected by the 99%/1% and 99% principles.

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