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Due to their low costs and excellent fire-resistive performance, gypsum board products for roof and wall assemblies are widely used in the North American construction marketplace. In 2004, U.S. manufacturers shipped a record 34.24 billion square feet of gypsum wallboard and Canadian manufacturers shipped an additional record 3.55 billion square feet (source: Gypsum Association).

The vast majority of gypsum board products (both interior wallboard and exterior sheathing) are manufactured with a paper facer on each side of the gypsum core. It is becoming increasingly well understood by designers and contractors (and attorneys) that these paper facers can provide an ideal substrate for mold proliferation if they are allowed to become wet. It is for this reason that Georgia-Pacific has ceased production of paper-faced gypsum sheathing for exterior use:

“ ...Traditional paper-faced gypsum sheathing ... has significant limitation, including a lack of resistance to moisture ... If paper-faced exterior sheathing becomes wet and the project is ‘closed in’ without adequate drying, the paper on the face and back of the panel can provide an excellent environment for mold growth” (G-P news release dated April 2004). The simplest method for preventing mold growth on paper-faced gypsum is to just keep the boards dry during and after construction; however, the prudent architect or specifier may wish to substitute the more expensive sheathing boards that do not have paper facers. More and more, support for this position is found in leading industry publications, as evidenced by the alarmingly titled article, “Avoiding the Perils of Paper-Faced Exterior Gypsum Sheathing,” published by Eric K. Olson, PE in the February 2005 issue of The Construction Specifier magazine:

“Practically speaking, specifiers rarely have control over the ultimate quality of workmanship or any of the factors coming into play after construction. As such, the proper selection of mold-resistant materials to provide some ‘forgiveness’ due to construction errors or delays is of utmost importance.”

In other words, the construction specifier or architect can lessen his/her potential exposure to future mold litigation and better protect the building’s future occupants by specifying exterior gypsum board products that are manufactured to provide improved resistance to moisture infiltration and mold infestation. Considering the enormity of some recent mold litigation awards, it is clear that the increased costs for these mold-resistant materials are as economically (and socially) justifiable as the increasing levels of seismic detailing required for new structures, even when located in zones of low seismic risk.

However, if paper-faced gypsum board is specified at a project, the contractor must be aware of current industry standards for moisture protection and mold prevention:

GA-283-03 (Guidelines for Prevention of Mold Growth on Gypsum Board), issued by the Gypsum Association, provides basic standards for transportation, receiving, storage, handling and application of gypsum board products and emphasizes that “gypsum board must be kept dry to prevent the growth of mold.”

ASTM C 1280-04 (Standard Specification for Application of Gypsum Sheathing) states that gypsum sheathing “shall not be exposed to the elements for more than 30 days after it has been installed” and also requires that “the exterior face paper of the sheathing shall be dry prior to application of the . . . weather-resistive barrier.”

Compliance with ASTM C 1280 is prescribed within Chapter 25 of the International Building Code (IBC). The companion Commentary volumes of the IBC confirm, “With regard to weather protection, all gypsum products must be kept dry because of the deleterious effect of moisture.”

Similarly, Section R701.2 of the International Residential Code states, “Products sensitive to adverse weather shall not be installed until adequate weather protection for the installation is provided. Exterior sheathing shall be dry before applying exterior cover.”

In summary, building codes and industry standards require 100-percent weather protection of interior gypsum wallboard products and forbid the contractor from closing in paper-faced gypsum sheathing products that have become wet. Despite these requirements, we continue to witness construction during the wet seasons where a contractor (who may be facing stiff financial penalties if the project is delayed) simply covers damp gypsum and wood products and hopes for the best. For some of these projects, a few simple photographs of these actions likely will prove to be invaluable weapons for the plaintiffs (and some codefendants) when mold/decay litigation later is initiated against the contractors.

This issue has been particularly problematic for contractors in jurisdictions regulated by the Uniform Building Code, which, in general terms, has calculated an exterior wall’s fire rating from both the interior and exterior sides—thus requiring the use of gypsum board products at both sides of the wall. In contrast, the IBC follows the lead of the “legacy” BOCA National Building Code by requiring, “The fire resistance rating of exterior walls . . . shall be rated for exposure to fire from the inside,” except for buildings located within five feet of property lines or other structures.

In other words, for a significant portion of the construction controlled by the IBC there is no fundamental design requirement for the use of gypsum sheathing at the outer face of exterior walls. (Note that this apparent reduction in fire-resistive performance is offset by increased requirements for sprinkler installation and performance at the building interiors.) Clearly, it is reasonable to expect that any design revisions and/or new product specifications that reduce the use of paper-faced gypsum sheathing at exterior walls will result in fewer mold claims.


June 2007
Issue Six, Volume Two

This article by Colin Murphy and Lonnie Haughton.

Colin Murphy
Murphy is a founder and managing partner of Trinity | ERD.

Lonnie Haughton
Haughton is a construction codes and standards consultant with Richard Avelar & Associates.

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