The great irony of "green" building is that the very concepts intended to enhance a building's performance over its entire lifetime are many of the same things that make a building highly susceptible to moisture and mold problems during its first few years of operation.
While green buildings have many positive benefits, strong evidence suggests a direct correlation between new products and innovative design and building failures. Simply put, departing from the "tried and true" often means increasing the risk of building failure.
Two strong characteristics of most green buildings are: 1) the use of innovative, locally-produced products, and 2) the implementation of new design, construction, and operation approaches intended to reduce energy usage and be environmentally sound.
Some of the differences between green buildings and the concepts the authors have found in lower risk buildings are summarized in the chart on page 41. For example, lower risk buildings do not exceed industry guidelines on mechanically introduced outside air; but rather emphasize humidity control (especially in hot, humid climates). Green buildings, on the other hand, reward the introduction of more outside air than current industry standards, which can lead to indoor humidity problems and mold growth.
Green building environmental goals are typically organized around a set of nationally accepted benchmark guidelines, such as those of Leadership in Energy and Environmental Design (LEED(R)), which is the guideline established by the U.S. Green Building Council (USGBC). LEED certification is a checklist and point system of recommended practices where achieving various point levels can certify the building as having achieved silver, gold, or platinum status. These practices involve such issues as efficient water and energy use, the reuse of waste materials, and the use of renewable and regionally produced products.
A New Leaf, New Risk
The overall goal of these new materials and procedures is to achieve a structure with reduced negative environmental impact, both during construction and throughout the building's life. The intent of building green is unquestionably noble and good, and should be aggressively pursued. However, this will introduce dramatic change to the design and construction industry. Its implementation will undoubtedly present new risks that are likely to be both technical and legal in nature.
Some of the legal risks are fairly obvious, such as the risk of not meeting a building owner's expectation of achieving a certain level of LEED certification -- implied or even written warranties. Other risks are more obscure, such as:
- The failure of new products to meet their promoted performance levels, which is more likely with new materials compared to proven materials found in traditional buildings.
- Accepting the higher standard of care that a green building might present -- what is currently considered "best practices" may now become the new expected "standard of care."
- Failing to recognize (or prepare for) the impact of a green building, in terms of unknowns in cost and schedules.
It is even unclear if a LEED-certified building can be built under a design/build method without the construction team assuming huge amounts of unknown risks because of the vague definition of what is considered "green."
The building industry has been historically conservative, relying on time-proven construction materials and methods. The introduction of new materials and methods has not always proven to be successful. In fact, this has sometimes resulted in notable building failures, especially those related to moisture intrusion and mold contamination. Many of the time-tested materials found in lower risk buildings are hydrocarbon-based. The long-term efficacies and performance levels are unproven for some of the new carbohydrate-based materials that are currently being promoted for green buildings.
The proliferation of new products and innovative building approaches related to green development is challenging the design and construction community in such a dramatic fashion. These changes virtually guarantee an increase in building failures and lawsuits. Past experience indicates that many of these failures will be predictable, and some are likely to be catastrophic.
Technical Risks for Contractors
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.
Some of the expandable foam insulation products are examples of green materials that pose increased risks. The water absorption properties of these insulation materials can be quite different than what designers expect with traditional insulation. Additionally, some of the carbohydrate-based foam insulation materials may retain more water than traditional hydrocarbon-based foam insulation. Increased absorption of water into the insulation could negatively affect the wall performance. This is not to say that such materials should not be used. However, their properties need to be recognized and accommodated in the design.
A Look at Moisture and Ventilation
The amount of ventilation (outdoor air) necessary for occupant health and comfort has been debated for decades. Although there are sound arguments on both sides of the debate, the emphasis on increasing ventilation to achieve LEED environmental quality credits has increased the incentive to add more outdoor air to a building through its HVAC system (a minimum of 30 percent more outside air above ASHRAE-recommended minimums is required to obtain a LEED credit for ventilation).
Increased ventilation is especially risky in the southeast U.S., where outdoor relative humidity levels are elevated for a good part of the year. Experience in the southeast, as well as other areas of the country with humid summers, has shown us a direct correlation between the number of moisture problems and increased ventilation rates.
To effectively minimize the risk of moisture problems while increasing ventilation, designers may need to increase the complexity and capacity of the HVAC components and control systems to achieve proper dehumidification. This adds to contractor risk, as complex systems historically fail more often than simple systems. Additionally, the complexity of the system operation can result in unintended pressurization relationships where local depressurization causes humid outdoor air to be drawn into interstitial building cavities, causing condensation and mold growth.
Building owners, designers, and contractors all assume more risk when they deal with complex -- and possibly untried -- technologies not generally found in traditional buildings. Pinpointing whether the problem is design- or construction-related may be very difficult after problems have already occurred.
Building startup procedures to meet LEED credits include a credit flush-out of indoor containments using increased outdoor air either at the end of construction or during the initial occupancy period. The intent is to remove pollutants from off gassing of volatile organic compounds (VOCs) from new materials. The amount of air needed to meet the flush-out requirements places a building at increased risk because of the amount of moisture introduced with the increased outdoor air.
LEED requirements are that a minimum of 14,000 cubic feet per square foot of floor area is required for flush-out. This presents multiple problems: Most HVAC systems are not designed to dehumidify that amount of outdoor air which, in a 100,000 square-foot building, is 1,400,000 cubic feet of outside air. Depending on outside conditions at the time of the flush-out, as much as 240,000 gallons of water can be added to a 100,000-square-foot building. This added moisture will be absorbed into building materials, finishes, and furnishings, increasing the risk of mold growth.
Most specifications put the general contractor in charge of the flush-out, including controlling relative humidity levels during flush-out. If the system is not designed to handle such loads, then the contractor faces a difficult challenge that may require the addition of a temporary (and extremely costly) dehumidification system. Lower risk buildings tend to avoid flush-out.
The Cost of Underperformance
What is the greatest risk to the green building movement? It's likely not the increased costs associated with green buildings. It's more likely green buildings that don't perform to expectations and, in some cases, may experience significant failures.
The increased costs of litigation and insurance that could result from underperforming green buildings will be absorbed by designers (in a highly competitive marketplace); however, in most cases will be passed onto building owners. These increased costs -- along with the negative publicity on failed green buildings -- could dramatically influence building owners not to build green.
Only recently has the marketplace begun to recognize the various contractual, legal, and technical risks that are inherent to green buildings. A growing number of experts have suggested that the first two steps to improved green building risk management are to: recognize the unique risks for green buildings and develop a set of guidelines that merge the unique regional challenges with green building guidelines, recognizing the lessons learned in lower risk buildings.
The design-and-construction community must not assume that if one builds green, then one will be building regionally correct or even lower risk buildings. Until the gaps between lower risk buildings and green buildings are addressed, the design community would be advised to prioritize the lessons of lower risk buildings already learned from the waterproofing, humidity control, and building forensics community. Without these priorities, poorly functioning green buildings are the likely result, and this could be the ultimate killer for the green building movement, especially in demanding climates.