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The Risks of Unwanted Exposure
- Protect Buildings from Mold During Construction
By Eric Olson, PE and Werner Gumpertz, PE


There is a 'new kid' on the block, able to complicate construction work and destroy newly-installed building components with relative ease. Eviction of this unwanted tenant may drive construction costs upward dramatically, lead to substantial delays in project completion, and cause nightmares for owners, contractors, and designers alike.

This unwelcome guest is biological contamination by harmful mold. The problems and health risks involving mold in occupied buildings have become well-publicized in recent years, and unfortunately, incidences of mold growth in uncompleted or newly-constructed buildings are on the rise. In some cases, the widespread growth of mold is established within the building well before its completion. While this trend probably results from many things, the following are significant contributing factors:

The use of building components vulnerable to water damage and capable of sustaining mold growth has become popular over the past few decades. These materials - including paper-faced gypsum wallboard and sheathing, paper-faced batt insulation, oriented strand board sheathing (OSB), and cellulose-based fireproofing-tend to be either concealed or have surfaces concealed within the walls.

The only adequate defense against mold infestation is systematic prevention, involving both a quality and durable building design, and construction methods that protect all vulnerable components until the building envelope is complete. While investigating problems with a new addition to a historic public building, we at Simpson Gumpertz and Heger Inc. encountered mold infestation. This project illustrates factors that can lead to mold growth and the costly measures required to remove mold-contaminated materials from the building.

The invitation is sent

The job involved a large addition to an historic public building, having exterior walls constructed of a conventional, brick veneer-/steel stud-framed wall system. Paper-faced gypsum wallboard and exterior sheathing covered the interior and exterior faces of the framing, with glass fiber batt insulation filling the space between. The veneer was fastened to the back-up walls with triangular ties and separated from the back-up with a cavity, while asphalt-impregnated felt paper covered the exterior sheathing. Structural steel framing was fireproofed with a non-asbestos, sprayed-on material. Pitched roofs draining to eaves above the exterior masonry walls covered much of the structure, with a low slope roof-covered area separating the addition from the existing building.

The project was well underway when the general contractor went bankrupt and stopped work. The contractor had finished construction of the exterior walls but not the roofing; the roof deck was left temporarily covered, but without watertight perimeter flashings or a temporary cover around the exterior walls. Conditions such as unterminated rubber roof membrane at roof edges, staging penetrations through temporary roof waterproofing, and unfinished dormer cheek walls exposing the wall interior allowed water to drain into the exterior wall system and building below.

The construction contract was assigned to the insolvent contractor's bonding company, which did not mobilize another contractor to continue the work until the following year. Meanwhile, water continued to enter the exterior wall system through the uncompleted roof system.

The guests arrive

The architect contacted our firm to determine the extent of structural damage sustained by the wall system due to water leakage that occurred during the construction delay. Through observations of the concealed wall spaces at isolated openings in the brick veneer and interior wallboard, and by visually inspecting the components with a borescope, we found mortar blockage of wall cavities and poorly constructed wall flashings. This reduced the wall system's ability to remove the water admitted into the cavity at the roof.

More significantly, however, we found extensive colonies of mold in the glass fiber batt insulation, and on both the interior and exterior drywall sheathing. Mold and mushrooms grew on the spray-on fir proofing of structural steel columns in the exterior wall. The damage was spread over most walls, but concentrated on the north wall.

Mold requires favorable conditions to grow and become established to the point where it presents a problem. It needs a source of food to sustain its growth. In this building, the food that fueled the mold growth was the cellulose contained in the paper facings on the interior and exterior gypsum wallboard, and the fireproofing on the steel framing.

The mold also needed a moist and humid environment, which must be maintained for a prolonged period of time. At this building, the failure to protect the vulnerable wall components from water intrusion, and a construction sequence that allowed water and mold-susceptible materials to be installed prior to making the building exterior watertight, created the ideal environment for these unwanted guests.

Some molds typically attracted to wet building materials can constitute a significant health risk, usually from toxins produced by the molds or by the allergic reactions they can cause in sensitive individuals. To establish whether potentially harmful molds were present, a consultant retrieved mold-contaminated materials and analyzed them in a laboratory. Table I lists molds that were not only present in this building, but commonly found on damp construction materials.

Analyses revealed molds presenting an unacceptable risk to future occupants were thriving in the building's exterior walls. All mold growing within the walls had to be removed.

Overstaying their welcome

Removal of mold from construction materials can be difficult and labor- intensive, or practically impossible. Smooth, non-porous surfaces, such metal or glass, can usually be decontaminated in-place with appropriate disinfection methods, provided the surfaces are accessible. Molds cannot generally be removed from porous surfaces, and cannot be removed from culturing, or 'food' surfaces such as paper gypsum board facers.

Once contaminated by mold, porous or culturing components generally require removal and replacement, involving the demolition and removal of affected areas. Since the affected materials are usually in confined spaces, the costly and labor-intensive demolition of unaffected but covering components (such as brick veneer and interior finishes) may be required to access and replace these elements. Since we found the mold growing on the steel column fireproofing, the interior drywall, insulation, and exterior gypsum sheathing, all the affected drywall and insulation had to be removed to prevent serious health risks to building occupants. The scope of abatement work involved the following:

As with the abatement of asbestos, the process of exposing and removing contaminated materials disturbs the mold, which can release harmful substances into surrounding areas. This can contaminate adjacent surfaces and furnishings, creating a hazard for workers and occupants in the affected space if proper steps to protect workers from contaminants are not employed.

There are currently no federal regulations, guidelines, or industry standards establishing acceptable levels of mold. An industrial hygienist competent in the field of mold abatement will help, determine whether mold observed within a given building, as well as its removal and abatement, constitutes a risk.

Lessons learned

Common sense dictates interior finishes should not be applied until the building is enclosed and made permanently watertight. Other steps to reduce the risk of mold growth in buildings under construction (also based on common sense) include the following:

Material selection

The composition of building materials has changed significantly in the last generation, containing more and more cellulose and other `food' surfaces. Selecting durable, less mold-susceptible exterior materials, such as glass fiber-faced sheathing instead of paper-faced sheathing, can reduce the risk of mold growth should water enter the exterior wall during (or after) construction.

Building envelope design

The design of the building exterior must recognize that any water intrusion can potentially foster mold growth. Designs cannot rely solely on sealants to keep water out of the building; `surface sealed' wall systems lacking drainage provisions and flashings to remove admitted moisture must be avoided in favor of walls with well-designed flashings and waterproofing. Waterproof sheet protection should be included in any event, since the single wythe brick veneer is not a waterproof wall component, and good design of this type of cavity wall calls for protection for long-term service.

Construction oversight

All building construction should be fully and continuously inspected by the general contractor, who is responsible for the protection and delivery of the final product. The contractor must perform the following, in a proactive and timely manner, before damage occurs:

Role of designer and owner representative

A competent owner representative and the designer must scrutinize the contractor's oversight to ensure he is complying with the contract requirements and acting in the owner's best interests.

They must also be prepared to deal with unforeseen issues, such as contractor bankruptcy. In lieu of the excuse, "leave means and methods to the contractor," the designer should specify and enforce proper sequence and installation of building components. If such steps are not taken and enforced, an indifferent contractor will sequence the installation in the cheapest and quickest possible manner, perhaps even installing interior finishes before a roof is completed.

'Single source' contractor for building envelope

There is a disturbing trend involving the increased alienation between trades traditionally involved with construction of the building exterior. The envelope must function as a well-integrated system; however, the multitude of trades involved in delivering the building envelope system (i.e. masons, carpenters, sheet metal workers, glaziers, waterproofers, roofers, and window and curtain wall erectors) do not generally understand the importance or function of the work of the other trades.

It is also apparent that some general contractors fall short in their ability or willingness to coordinate trades to properly sequence and assemble the envelope in the order required to provide a viable exterior wall system. Many failures that allow water to enter buildings do not occur within a given system, but occur at transitions between systems installed by different trades (such as transitions between masonry through-wall and window flashings, transitions between roof flashings and exterior walls, and so forth).

It comes as no surprise these failures are the most difficult to correct due to the fingerpointing that generally ensues. It is in the owner's best interest to seek a single-source building envelope contractor who possesses the in-house experience, knowledge, and forces to properly sequence, coordinate, and assemble the entire envelope system.

Conclusion

The change in design selections over the last generation has resulted in:

Design and construction practices have not changed sufficiently to deal with these advances in building technology.

The industry must come to grips with the risk presented to the owner's property and the designer's reputation when a contractor stops work because of a strike, contract dispute, shortage of funds, or bankruptcy. Bonding companies are often reluctant (sometimes for good reasons) to assume responsibility for the continuation of the project. The owner and designer must insist that at least temporary protection is provided to protect sensitive components from weather exposure and abuse. Bonding organizations must be promptly alerted to the need to minimize damages as soon as the construction work is put at risk.

Unwanted exposure of a building during construction constitutes a significant risk of collateral damage if the contractor's work is unexpectedly interrupted. Among the risks are not only the known problems, but also those involving molds nesting on organic surfaces. These risks threaten disproportionate damages to wall components and other elements exposed to uncontrolled weather exposure, mostly because of inaccessibility of affected surfaces.

Not surprisingly, quality and properly sequenced construction, along with vigorous inspection are proven measures for limiting damages even in the unforeseen event of a construction stoppage. In addition, transitional, protective measures should be built into the routine of project takeover by bonding companies to limit damages.

References

U.S. Environmental Protection Agency, Mold Remediation in Schools and Commercial Buildings, EPA 402-K-01-001 March 2001.

NCEH (Center for Disease Control and Prevention) National Center for Environmental Health, "Questions and answers on Stachybotrys chartarum and other molds: (last reviewed 14 March 2002)."

Acknowledgments

The authors thank Steven B. Bloom, MS, Environmental Health and Engineering Inc. of Newton, Massachusetts, for his review of this article and help with Table 1. The authors also thank the principals and associates of Simpson Gumpertz and Heger Inc. of Arlington, Massachusetts, for their support.

Authors

Eric K. Olson, PE, a staff engineer with Simpson Gumpertz and Heger (SGH) Inc., specializes in the investigation and remediation of problems involving building envelope systems, including exterior wall systems and cladding, windows, and roofing. He is a member of the American Society for Civil Engineers (ASCE), and can be reached via e-mail at ekolson@sgh.com. Werner Gumpertz, PE, co-founded SGH in 1956, and has investigated, written about, and lectured on roofing, waterproofing, curtain walls, masonry, flooring, and building and concrete technology. He is a member of a number of engineering organizations, and won the 1987 American Society for Testing and Materials' (ASTM's) Walter C. Voss Award for Outstanding Contribution to the Advancement of Building Technology, and the Honor Award for Design in Urban Transportation from the U.S. Department of Housing & Urban Development (HUD) in 1968.-Gumpertz can be reached via e-mail at whgumpertz@sgh.com.

Reprinted with permission of The Construction Specifications Institute, 99 Canal Center Plaza, Suite 300, Alexandria, VA 22314, from the Construction Specifier.

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