The great irony of building green 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, there is also strong evidence to suggest a direct correlation between new products/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 that are intended to reduce energy usage and be environmentally sound.
The preceding graphic summarizes some of the differences between green buildings and the concepts the authors have found in lower risk buildings. For example, lower risk buildings do not exceed industry guidelines on mechanically introduced outside air; but 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 尝贰贰顿庐 (Leadership in Energy and Environmental Design), which is the guideline established by the United States Green Building Council (USGBC). 尝贰贰顿庐 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.(1)
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, because of the dramatic change that this will present to the design and construction industry, its implementation will 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 尝贰贰顿庐 certification (i.e., implied or even written warranties). Other risks are more obscure, such as:
Green Buildings vs. Lower Risk Buildings
Green Buildings | Lower Risk Buildings |
Adds additional outside air (>ASHRAE by 30+ %) | Minimizes outside air (Does not exceed ASHRAE guidelines) |
Emphasize energy conservation | Emphasize dehumidification |
Stress VOC reduction --Emphasizes exhaust (>5 Paschals) --Building flush out | Minimizes VOC concern --Very tight control of exhaust --Rejects building flush out |
Stress new, innovative materials | Stress proven materials |
Stresses carbohydrate based materials | Stresses hydrocarbon based materials |
Stresses extra envelope thermal insulation | Stresses drying potential of envelope (walls and roof) |
- 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 unknowns in cost and schedule impacts that a green building might present.
- Vegetative roofs, which are more risky than conventional roofs (due to the constantly wet conditions) and must be carefully designed, constructed, and monitored after construction.
- Improved energy performance through increased insulation and the use of new materials, which may change the dew point location in walls, resulting 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," which could 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 1980's by the indoor air quality industry, which often caused more problems than they solved.
- Development of a set of Climate Design Criteria that integrates (and prioritizes) climate-specific criteria with current green building practices. Best practices for moisture control must take priority over green building practices.
- Development of a detailed Green Building Risk Management Plan that provides guidelines for the design and construction team from concept through the 1-year warranty period. These guidelines would incorporate the best ideas of green building specialists, moisture control specialists, construction attorneys, and insurance companies.
- Apply the lessons learned from past building successes and failures and make green building concepts subservient to these past lessons.