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Using Standard Moisture Modules Gives Wall Designers an Edge

A task group of ASTM Subcommittee E06.41 on Air Leakage and Ventilation Performance seeks participation as they develop a “Standard Guide for the Selection and Use of Modeling for Moisture Control Design in Building Envelopes.” The ASTM group invites architects, building designers, inspectors, forensic experts, and any interested party to join this activity.

“The proposed standard will develop a consistent approach in classifying different moisture design approaches using modeling,” says task-group chairman Achilles Karagiozis, Ph.D., senior research engineer, Hygrothermal Project Manager, Oak Ridge National Laboratory, Oak Ridge, Tenn. “The standard will define the underlying fundamentals of each model used in any moisture control design activity. The inputs, assumptions and results will be developed into distinguishable methods of analysis.

“We have a great opportunity to develop better-designed building envelopes for moisture control using modeling,” Karagiozis says. “The current hot issues of mold/fungal growth in building envelopes will be a thing of the past if we start designing wall systems that can handle unexpected moisture loads. Modeling allows us to do exactly that.” According to Karagiozis, a moisture model is “a steady state or preferably transient model of the fundamental heat, air and moisture transport in single or multi-component building envelope systems.” He says moisture models include:

• Storage;
• Evaporation/condensation;
• Freeze/thawing;
• Vapor diffusion; and
• Capillary suction, thermal, or air transports.

According to Karagiozis, the subcommittee proposed the standard because numerous heat-and-moisture transfer models have recently been developed. “With the proliferation of mold and water damages in today’s building construction,” he says, “better moisture control design of building systems is demanded by the public and other institutions. Currently, hundreds of building-envelope engineers and architects are using modeling for moisture-control design. However, a consistent approach in conducting a design investigation is not available. At the same time, it is hard to distinguish the fundamental characteristics of the various models by the design community. This makes the interpretation and validity very difficult to confirm.”

Using standard moisture models gives wall designers an edge, he says: “The benefit gained is that the designer is now able to investigate the sensitivity of a particular design to slight changes in materials changes, construction layout, and the effect of different climatic conditions. Use of modeling can provide the performance characteristics that a design may use to help select the best performing envelope systems for particular indoor and outdoor environmental loads.”

To participate or obtain further information, contact Achilles Karagiozis, Ph.D., Hygrothermal Project, Oak Ridge National Laboratory, Oak Ridge, Tenn. (phone: 865/576-3924). Read about U.S. research on moisture models here. ASTM Committee E06 meets Oct. 19-22 in Tampa, Fla. For meeting or membership details, contact Steve Mawn, manager, Technical Committee Operations, ASTM International (phone: 610/832-9726). //

Copyright 2003, ASTM