Moisture intrusion, whether bulk water intrusion through the building envelope or a relative humidity increase because of the heating, ventilating, and air conditioning (HVAC) system, results in a large percentage of construction claims in the U.S. Moisture intrusion not only results in building deterioration, but has been linked to occupant comfort and health issues, especially in those buildings that become contaminated with mold. Sustainable building practices, some of which are part of the LEED accreditation process, can increase the potential for moisture intrusion if not carefully considered and implemented. Examples include:

Vegetative roofs, which are more risky than conventional roofs (because of the constantly wet conditions), must be carefully designed, constructed, and monitored after construction.
E Improved energy performance through increased insulation and the use of new materials, which may change the dew point location in walls, can result in damaging condensation and a reduced drying potential for wall assemblies. Lower risk buildings emphasize the drying potential of the envelope over increased insulation. While it is desirable to increase insulation for energy savings, the designer must also evaluate moisture impacts.
Reuse of existing buildings or recycled components, which may not provide optimum water-shedding performance in new configurations or may not be readily integrated to the adjacent new materials.
Use of new green construction materials that have not been field-tested over time. The designer needs to assess new materials and their risks compared to traditional materials found in lower risk buildings.
Increased ventilation to meet indoor air quality (IAQ) goals that may unintentionally result in increased interior humidity levels in hot, humid climates. The designer must consider the increased energy load (and cost) and HVAC equipment sizing required to properly dehumidify a building when exceeding the minimum outside air requirements recommended by the American Society of Heating, Refrigerating, and Air-conditioning, Engineers (ASHRAE).
Building startup procedures, such as "building flush out," can result in increased humidity levels and mold growth. Lower risk buildings rely almost exclusively on source control (which is also a green building goal) rather than relying on "flush-out" and increased building exhaust. Building "flush out" along with building "bake-out" were concepts developed in the late 1980s by the indoor air quality industry. These building concepts often caused more problems than they solved.

New green construction materials are entering the market at a staggering rate. Because many of these products help to achieve multiple LEED credits, designers working on green buildings are eager to specify these materials. The risk to contractors is that many of these new items are not time-tested, and designers often do not have the time to fully research their efficacy. If the new product fails, then it may be difficult to determine if it is a design error, an installation error, or a product defect. Additionally, general contractors must rely on subcontractors to install new materials that they are inexperienced in installing.

Special Reports /

Hidden Risks of Green Buildings

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