Friday, March 1, 2013


For envelopes to function as intended requires proper attention to

● Selection and design of compatible materials and systems
● Proper detailing of material junctions and terminations
● Installation and inspection of these details during construction
● Ability of composite envelope systems to function during weathering cycles
● Maintenance of the completed envelope by building owners

From the multitude of systems available to a designer, specific products that can function together and be properly transitioned must be chosen carefully. Once products are chosen and specified, proposed substitutions by contractors must be thoroughly reviewed.

Similar products may not function nor be compatible with previously chosen components. Substitutions of specified components with multiple, different systems only further complicate the successful installation of a building envelope.

Improper attention to specified details of terminations, junctures, and changes in materials during installation can cause water infiltration. Once construction begins, installation procedures must be monitored continuously to meet specified design and performance criteria and manufacturers’ recommendations. Detailing problems compound by using several different crafts and subcontractors in a single detail. For instance, a typical coping cap detail (Fig. 1.10) involves roofing, carpentry, masonry, waterproofing, and sheet metal contractors. One weak or improperly installed material in this detail will create problems for the entire envelope.

Typical coping cap detailing and the subcontractors involved.
FIGURE 1.10 Typical coping cap detailing and the subcontractors involved.

Finally, products chosen and installed as part of a building envelope must function together during life-cycling and weathering of a structure. For example, an installed precast panel might move over 1 2 in during normal thermal cycling, but the sealant installed in the expansion joint might be capable of withstanding only  1 4-in movement.

Proper maintenance after system installation is imperative for proper life-cycling.

Will shelf angles be adequate to support parapet walls during wind or snow loading?
Will oxidation of counterflashing allow water infiltration into a roof system, causing further deterioration?

From these processes of design, construction, and maintenance, 99 percent of a building envelope typically will function properly. The remaining 1 percent creates the magnitude of problems. This 1 percent requires much more attention and time by owners, architects, engineers, contractors, and subcontractors to ensure an effective building envelope.

The most frequent problems of this 1 percent occur because of inadequate detailing by architects, improper installation by contractors and subcontractors, and improper maintenance by building owners. Typical frequent envelope errors include

● Architects and engineers. Improper detail specifications (90%/1% principle); no allowance for structural or thermal movement; improper selection of materials; use of substitutes that do not integrate with other components of the envelope.
● Component manufacturers. Insufficient standard details provided for terminations and transitions; inadequate training for installers of materials; insufficient testing for compatibility with other envelope components.
● General contractors and subcontractors. Improper installations (99% principle); inattention to details; no coordination between the various envelope subcontractors; use of untrained mechanics to complete the work.
● Building owners and managers. No scheduled maintenance programs; use of untrained personnel to make repairs; no scheduled inspection programs; postponement of repairs until further damage is caused to the envelope and structural components.

Manufacturers are now concentrating on making technological improvements in the materials themselves rather than technological advances, specifically making their products “idiot-proof.” They realize that meeting industry standards does not correlate with success in field applications. In reality, products are subjected to everything that can possibly go wrong, from environmental conditions during installation to untrained mechanics installing the product. Never are products installed in the pristine conditions of a laboratory.

Making their products with “belt and suspenders” protection increases the likelihood of success, at least for the individual system—for example, products that no longer require primers, no mixing of two component materials but now one-part materials, pressure rinse versus pressure-wash preparation, and 300% elongation rather than 100% to add additional protection against excess movement or in-place service requirements.

Similar quality advances at the job-site level by contractors to adequately apply the precautions necessary to protect against the 90%/1% and 99% principles will eliminate the vast majority of waterproofing problems that now plague the industry.

No comments:

Post a Comment