Originally posted Monday, 13 September 2010
Written by David Odom, Richard Scott and George H. DuBose
Yesterday’s seal of approval for a new product was “It was developed by NASA.” Today the seal of approval is: it’s “organically produced,” “LEED-certified,” “earth-friendly,” or some variation of the above. Just as “NASA-developed” was no guarantee of success, neither is “LEED-certified” any assurance of high performance, especially in avoiding problems related to moisture and mold accumulation.
The Hidden Risks of Green Buildings
The Three Keys to Avoiding Moisture and Mold Problems
Yesterday’s seal of approval for a new product was “It was developed by NASA.” Today the seal of approval is: it’s “organically produced,” “LEED-certified,” “earth-friendly,” or some variation of the above. Just as “NASA-developed” was no guarantee of success, neither is “LEED-certified” any assurance of high performance, especially in avoiding problems related to moisture and mold accumulation. In fact, based on our 25+ years of experience in analyzing building failures, we believe that many of the concepts incorporated into green buildings make these structures particularly vulnerable to performance problems—some of which could be dramatically more significant than just excess energy usage.
While the goal of green buildings is undoubtedly a noble and deserving goal concept, there is a growing concern, especially among building scientists and forensic engineers, about the risk of green building problems as performance problems begin to become noticed. Although some indicators of a building’s performance (such as occupant comfort, energy usage, and minor odors) can be ignored, you can’t easily ignore water pouring through a wall assembly. We don’t believe that anyone would deem a structure “sustainable” if it cannot survive the first five years without a major renovation because of moisture and mold problems.
It’s our belief that the moisture integrity of a structure is one of the most important criteria in any new building. It’s also our experience that sometimes the final “report cards” don’t come for several years after the building is occupied and the problems finally have a chance to manifest themselves.
After reviewing the designs of hundreds of new buildings over the past 25 years and observing the failures in an equal number of structures, we have found the following consistent truths:
• Building Commissioning The current industry approach to building commissioning is unlikely to prevent moisture and other similar building failures in virtually every climate, except for the most forgiving climates.
• New Materials The use of many new building products often have the unintended consequence of performing in unexpected ways, sometimes encouraging significant moisture accumulation and mold growth.
• Increased Building Ventilation The positive benefits of increased outside air ventilation for the occupant’s health and comfort can oftentimes be outweighed by the increased potential for moisture problems, some of which have caused catastrophic failures even in fairly temperate climates. Forensic engineers and building scientists have strong evidence that buildings can perform in unexpected and often damaging ways when additional air is moved through them.
Though it is important to aim for environmentally friendly concepts in your building, it is equally important that it must be built with sustainability in mind to prevent major performance problems—moisture and mold problems historically being some of the most prevalent building deficiencies.
Green Buildings vs. Lower Risk Buildings
An important aspect to avoiding moisture problems in green buildings is to make sure green building practices are always subservient to good design practices in areas such as exterior waterproofing, humidity control, and due diligence in selecting new construction materials.
To facilitate the dual purpose of an environmentally sensitive building with a highly durable, well-performing, moisture-resistant building, we recommend keeping the following concerns in mind:
The current approach to building commissioning is not likely to identify and prevent catastrophic moisture and mold problems. This is because traditional commissioning fails to accomplish two primary requirements in avoiding moisture problems:
1. The design-phase review model is not likely to be a “standard of care” technical peer review but is often a review intended to: (1) Determine if the constructed building, once built, can be commissioned and (2) Confirm that the design meets the owner’s intent. In our experience, the typical design review will not predict the potential for “significant” building performance problems. Without this prediction, it cannot offer specific solutions to proactively avoid these potential problems.
2. These reviews are not required to include an analysis of the building envelope’s performance – the acknowledged building component that fails the most frequently and usually the most dramatically.
Because new green building materials often claim green attributes, they are frequently used. However, experience has demonstrated to building scientists that new products often mean increased failures—at least in the beginning.
If we accept the proposition that we are relatively unfamiliar with a new material’s long-term individual performance, then it is reasonable to assume that we probably know even less about the new material’s interaction with adjacent components within an assembly. The recognition of the additional risk in the use of innovative products (especially in the envelope and HVAC systems) by the development team demands a higher degree of rigor in the evaluation of these products than can be typically given during the normal design and construction process.
The use of new products mandates that throughout the design and construction processes, these materials should be more rigorously evaluated than we believe traditional products have been evaluated, and additional modeling and analyses should take place along the way.
Increased Building Ventilation
For decades there have been competing arguments on whether to increase or decrease the amount of outside air that is introduced into buildings. Although there are sound arguments on both sides of the debate, today’s “green” emphasis on increased building ventilation has given an added incentive to increase the amount of outside air to buildings. The experience of many building scientists do not necessarily support the theory that adding more outside air creates a better-performing, more sustainable building — sometimes quite the opposite.
The HVAC system that introduces ventilation air must also do so in a manner that properly dehumidifies (or humidifies) the air. The “golden rule” of moisture control is that under no circumstances should adequate dehumidification be sacrificed for increased ventilation. In many regions of the country during summertime conditions, the moisture load contributed by the outside air can exceed the amount of moisture that the air-conditioning system can effectively remove.
What experience demonstrates is that increased amounts of outside air can be safely added to a building if the known causes of increased risk (such as proper air distribution and increased moisture load) are addressed during design, and verified during, and after, construction.
Indoor Air Quality Management Plan
Immediately after construction there can be increased pollutant load in a building because of various factors: heavy airborne particulate counts and the off-gassing of volatile organic compounds (VOCs) from newly installed products. There are various methods of controlling this additional pollutant load, such as: (1) site-specific exhaust, (2) the use of low VOC materials, and (3) flushing out the building with additional amounts of outside air prior to (and immediately after) occupancy (i.e., building flush-out).
One of the additional risks with conducting building flush out is the significant amount of additional moisture (or latent) load that can be added to the building. This additional moisture risk is true for all but the driest climates. While we recognize that the guidelines require maintaining relative humidity levels no higher than 60 percent, we also recognize that these actions are often ignored. The additional likelihood that the HVAC system might still be unbalanced at the time of the flush out increases the potential for moisture problems as the result of this process.
We have calculated that the amount of air required to flush-out a typical 100,000 square foot building can add over 200,000 pints of moisture to a building in order to meet the goal of adding at least 14,000 cubic feet of outside air per square foot of floor space. Thus, while flush-out seems to be a fairly easy green building effort to achieve, it has historically proven to be both a risky and often costly endeavor.
Green design has brought to the forefront a holistic view of how to design, build, and operate higher performing buildings. As such, the noble goals espoused by sustainable development and green buildings are certainly worth aggressively pursuing — but this must be done with significant care, especially in the areas that are historically high risk for moisture and mold problems. It seems that some of the best practices and lessons learned in other fields are not applied in a precise manner when it involves green construction, at least as that applies to moisture control.
To summarize our recommendations, we believe that the following three steps should occur to improve the performance of green designs:
1. A robust technical peer review of the design should be implemented with a stated goal to predict the performance and possible failure of new materials and products.
2. The design team must be challenged by the building owner regarding whether they have incorporated historical institutional knowledge in the fields of humidity control, waterproofing, and building envelope performance. Processes that have long ago already lost favor in the indoor environment field, such as “building flush out,” should not now be incorporated into green construction as best practices. These processes have historically shown little benefit and have demonstrated high cost, high risk, or both.
3. The acceptance of new products with specific “green” benefits should be highly scrutinized. Products that gain performance in one area often sacrifice performance in another. If the sacrifice is a critical parameter (such as the water absorption qualities of wall insulation), then the risk may be too great, no matter what the green benefit is.
The authors are forensic engineers and architects with Liberty Building Forensics Group LLC (www.libertybuilding.com), a Zellwood, FL firm specializing in moisture intrusion, mold problems, litigation support/buildings forensics, problem-avoidance peer reviews, and implementation of green buildings. Their staff has led the correction and cost recovery for some of the largest building failures in the country and has performed green building-related services on over $3 billion in new construction since the mid-1990s. They have authored three manuals and over 100 technical publications which can be accessed by visiting their website. J. David Odom (firstname.lastname@example.org), Richard Scott, AIA, LEED-AP (email@example.com), and George H. DuBose, CGC (firstname.lastname@example.org) can be contacted at 407-703-1300 for more information.
*NOTE – THERE IS A TABLE GRAPHIC WITHIN THIS ARTICLE IN PRINT*