Technical Updates

A five-year study of 5,000 construction claims by the Design Professional Insurance Company (DPIC) found that the most prevalent building problems – corrosion, building material degradation, and mold – were moisture-related (Engineering News-Record 1991). Moisture comes from four sources, which have different priorities depending on climate.

• Rainwater intrusion. Moisture present in building materials and on the site during construction can be a source of problems. Significant amounts of moisture can also result from water leaks within building systems or through the building envelope. In both hot, humid and temperate climates, rainwater leaks are a major source of building moisture and microbial growth problems.

• Infiltration of outside moisture-laden air. Whether introduced by wind or through the HVAC system, air infiltration can cause condensation on interior surfaces, including inside building cavities. Condensation and high RH are important factors in creating an environment conducive to mold growth and are the primary problems in hot, humid climates.

• Internally generated moisture. After construction, occupant activities and routine housekeeping procedures can generate additional moisture, contributing to the mold problem. Normally, if no other significant sources exist, well-designed and properly operating AC systems can adequately remove this moisture.

• Vapor diffusion through the building envelope. Differential vapor pressure, which can cause water vapor to diffuse through the building envelope, is a less significant cause of moisture problems in buildings. Nevertheless, it is a mechanism to consider in building design and construction, particularly in cold climates and in hot, humid climates, and especially as it relates to the construction of vapor retarders in walls.

To be continued…

Shortly after construction was completed, a seven-story, four-star hotel in Charleston, South Carolina, developed severe moisture and mold problems. The investigators attributed the problems to rainwater intrusion through the hotel’s exterior brick veneer. Following that diagnosis, the hotel owner spent more than $10 million on renovations, including a completely redesigned and reconstructed building envelope.

The summer after the renovations were completed, the moisture and mold problems returned. While focusing on the envelope leaks, the investigators had overlooked the significant secondary source of moisture: outside air infiltration.

In areas like South Carolina, where hot, humid conditions persist, IAQ problems are largely due to a combination of high ambient moisture, improper interaction between the building envelope and the HVAC system, and misapplication of design and operation principles.

1) High ambient moisture – Given the high ambient moisture levels in humid climates during the summer months and the dehumidification limitations of many AC systems, excessive moisture accumulation within buildings and the resulting microbial growth are understandably major problems. Microbial-related IAQ problems in buildings can also occur in temperate climates, although more serious errors in the design, construction, or operation of a building normally must occur for such problems to develop in these areas. Cold climates are just as susceptible to moisture problems as hot, humid climates, and building envelopes must be designed accordingly. Many microbial problems in temperate climates are more commonly a result of water intrusion (rainwater and subsurface water) through breaches in the building envelope system, including subsurface envelope systems.

In all climates, anything that elevates the indoor RH or results in damp materials (leaky pipes, for example) for an extended period can cause microbial IAQ problems. Landscape irrigation systems, indoor swimming pools, and building humidification systems can provide enough moisture to create microclimates and microbial growth problems, even in dry climates. Buildings in Boise, Idaho; Denver, Colorado; and Kona, Hawaii have all been hit with severe IAQ problems from microbial growth as a result of introduced moisture, despite the fact that they are considered arid climates.

To be continued…

Comparing the latent and sensible loads for several major cities in different geographic regions (Peart and Cook 1994) helps illustrate the new definition. A study was done showing the monthly average latent and sensible loads from outside air for Orlando, Florida; Atlanta, Georgia; and Columbus, Ohio. During the cooling season in Orlando, the latent load far exceeds the sensible load of outside air. The effect of these conditions, which occur for more than half a year, is that any outside air drawn into the building envelope or occupied space will likely cause moisture accumulation and microbial growth problems. Furthermore, because this outside air is used for ventilating the building’s occupied spaces, it presents a huge dehumidification challenge for the makeup air system. Clearly, under these conditions, Orlando is highly susceptible to moisture intrusion problems.

Atlanta was shown to be less susceptible to moisture intrusion problems than Orlando because, on average, the difference between sensible and latent load is small, particularly during the peak cooling months. Standard AC systems have a better chance of accounting for the latent load in Atlanta than in Orlando. Nevertheless, the latent load in Atlanta represents enough of a moisture accumulation risk that it belongs within the upper boundary of the humid zone. However, according to the ASHRAE-defined humid zone, Atlanta is outside the critical zone for humid conditions.

When looking at Columbus, the latent load from outside air is consistently less than the sensible load. The reversal of the load relationship explains why buildings in Columbus are not likely to develop moisture-related problems from outside air intrusion, because any outside air that infiltrates into buildings in Columbus will be adequately dehumidified before it is cooled.

The new definition also explains why, in certain areas of the country, building commissioning procedures are more critical than in others. For example, if the building exhaust systems are started before the AC and makeup air systems, as is typical, huge amounts of moisture may infiltrate the building, depending on the outdoor conditions.

In applying the new humid climate definition, however, two qualifications must be made:

• The definition is based on average climatological data. At certain times during the summer, the latent load of outside air can exceed the sensible load to a much greater extent than was reflected in the study. Such episodes of extreme high moisture entering the building can cause problems despite seemingly safe average conditions and must be considered in problem prevention.
• If the building envelope has an improperly located vapor retarder, moisture accumulation problems can occur, even if a favorable sensible/latent load relationship exists. Condensed moisture behind the vapor retarder will never reach the AC system for proper dehumidification but will accumulate in the wall system. Thus, architectural aspects of the building work in conjunction with outside conditions to create problems.

To be continued…

According to ASHRAE, a humid climate can be defined as one in which one or both of the following conditions occur:

1) A 67 degrees Fahrenheit [20 degrees Celsius] or higher wet bulb temperature for 3,000 hours or more during the warmest six consecutive months of the year.

2) A 73 degrees Fahrenheit [23 degrees Celsius] or higher wet bulb temperature for 1,500 hours or more during the warmest six consecutive months of the year.

This definition is somewhat problematic. First, it is difficult to interpret and apply to problem solving. Second, high dew-point conditions can also indicate areas where moisture problems occur. Atlanta, Georgia, for example, does not qualify as a humid climate under the ASHRAE definition, but high dew points are experienced in this area and problem buildings are often found there.

Industry experience with building failures suggests the need for a new definition of humid climates that more clearly identifies the geography where problem buildings are more likely to be found, and better explains why these problems occur at all. This new definition is based on observations about latent and sensible load: A humid climate is defined as one where the average monthly latent load of outside air meets or exceeds the average monthly sensible load for any month during the cooling season. (Latent load is the moisture in outside air that is brought into the building and requires removal via dehumidification. Sensible load is the air temperature that is sensed and addressed by the HVAC system, either by heating or cooling the air, to reach the established set point.)

Infiltration of air with a high latent load will cause moisture to accumulate in building materials such as gypsum wallboard, with subsequent material degradation and mold growth. This infiltration may also exceed the ability of the HVAC system to remove moisture from the supply air. On any given day in many temperate areas, the latent load may be greater than the sensible load without causing problems; however, when these conditions persist for a longer period (a month, for example), the resulting moisture accumulation is sufficient to cause building failure.

The occurrence of a high latent load during the cooling season is a critical factor in building failure. Thus, defining hot, humid climates in terms of the relationship of sensible to latent load in ambient air expands the ASHRAE humid climate zone to include other parts of the  United States that are highly susceptible to moisture-related building failures.

To be continued…

In the summer of 1988, construction of a large luxury resort was coming to a close. Because the vinyl wall covering on the interior side of the exterior walls had an impermeable finish, it functioned as a vapor retarder (also referred to as a vapor barrier). The HVAC system consisted of a continuous toilet exhaust and packaged terminal air-conditioner (PTAC) units. The outside air exchange rate in each guest room averaged six times an hour, all from infiltration. In this case, problems developed inside the building and inside the wall.

The combined effect of excessive outside air infiltration and an improperly located vapor retarder caused $5.5 million in moisture and mold damage, even before the facility was opened. If these same design combinations had occurred in a more temperate climate, the problems would have been limited to increased energy consumption and possibly to complaints about guest comfort.

This is one example of how hot, humid climates present unique challenges that are often overlooked by the design and construction community. However, challenges also occur for buildings located in other climates. Meeting these challenges depends on understanding a building’s local climate conditions and how those contribute to IAQ problems.

Cold climates offer challenges for moisture flow through the building envelope that are similar to those in hot, humid climes. Cold climates are defined by the American Society of Heating, Refrigerating, and Air Conditioning Engineers (ASHRAE) as those that experience at last 4,000 heating degree days (HDD at 65 degrees Fahrenheit [18 degrees Celsius] base) per year. Most problems occur during the winter, when the warm and relatively moist interior air is forced (due to high differential vapor pressures between indoors and outdoors) to the dryer and colder outdoor conditions. Moisture flow can be trapped and condensed on an improperly located vapor retarder. In addition, if the building is air-conditioned during the summer, the wall systems designed to address the heating condition can experience moisture damage inside the walls during the air-conditioned months. Therefore, few locations in the United States are completely free of potential moisture problems.

To be continued…

The inevitable is about to happen and most people don’t even know it is coming — green buildings are going to become, by codification, the law of the land. For some firms, this will just mean business as usual. For other firms, this change will be cataclysmic.

ASHRAE produces standards that are adopted by most model building codes, and the ASHRAE Draft Standard 189.1P is the new “Standard for the Design of High Performance Green Buildings Except Low-Rise Residential Buildings.”

This new ASHRAE Standard (currently in its final draft) is written in code language and will have the impact of mandating that all new buildings will be green buildings, thus eliminating the option of constructing anything less robust. Even if this standard is not adopted by all model codes, it will become the de facto standard of care. On the surface this sounds like a very good thing — mandating better-performing, more energy-efficient buildings – and it certainly has many redeeming aspects.

Here’s the downside:

• Lack of Experience Will Increase Design and Construction Deficiencies – Many of the optional aspects of the current USGBC LEED® guidelines will now be mandatory for designers and contractors. This means that, even if your designer or contractor doesn’t fully understand the key technical issues (e.g., envelope air barriers), they will still be required to use them. This practice of forcing designers and contractors to implement building features that they don’t fully understand creates a dilemma in the industry: either represent yourself as technically savvy, or face certain extinction. Given these as choices, building failures becomes more likely as firms design and construct buildings with components that they do not understand in an effort to keep the work coming in.

• Standard of Care Will Be Elevated – These new code requirements will automatically raise the required standard of care for the design and construction industry. This will increase the risk profile of their projects and may (at least initially) trigger some exclusion clauses in their current insurance policies. What are now considered “best practices” will soon be considered the minimum standard of care.  

• Regional Issues Not Addressed – The new standard mandates national green building requirements throughout the country with very little regard of the unique regions of the country where certain concepts may not be appropriate. This is almost always a problem when national standards are uniformly imposed on climates with unique requirements (e.g., hot and humid, very cold, or very rainy climates).

The inevitable result is that everyone will quickly morph into a green practitioner and the true marketplace differentiators (those with experience and unique technical expertise) will become difficult to discern. While codes can dictate that the industry follows certain standards, it cannot mandate that they get correctly implemented — with an increase in design and construction deficiencies and lawsuits being the inevitable result.   

Recognizing that this new standard (due to be issued in final form in 2010) could be a game-changer in the building marketplace, what’s the path forward?

• Review a copy of the current draft version of ASHRAE 189.1P and begin to understand the impact of the new requirements on your firm’s business, insurance, risk management, and technical expertise. (Note: This is available on line from www.ASHRAE.org)
•  Identify what requisite skills and knowledge your firm will need once this new standard is implemented.
• As this draft standard is finalized, expect more updates from Liberty Building Forensics Group with our analysis on its impact.

This leaves water, in both liquid and vapor form, as the only element for fungal growth that we can easily control. Fungi need to break down nutrients before they can absorb them. They do this by secreting enzymes, which require the presence of water on the organic surface that is in contact with the fungal spores. Once the organic material has absorbed enough water, the fungal spores secrete the enzymes, absorb the dissolved nutrient, germinate, and begin to grow, sending out filaments called hyphae. These hyphae extend over the surface of the organic material, allowing the fungal growth to absorb more nutrients. As the hyphae thicken, they dig into the organic material forming a protective mat called a mycelium. This mat helps to hold in moisture, allowing the fungal growth to continue to feed even if the air is dry. Eventually the mass grows conidia, which generate new spores that are transported by air to other potential nutrient sources.

The amount of water in an organic material can be determined in a laboratory and given a quantitative measurement called water activity (aw). The required water activity varies by kind of fungi. Forensic investigators of building mold problems sometimes use this correlation to help determine the source of water that caused mold growth. Stachybotrys chartarum, which grows well on the paper surface of gypsum wallboard, needs a very high aw to grow. However, too much water can inhibit mold growth.

Liquid water from floods or rain can wet porous materials to the saturation point, often wicking up surfaces such as gypsum wallboard. Mold can grow after the gypsum wallboard dries to the aw needs of whatever fungal spores happen to be present. High indoor relative humidity can cause condensation on cooler surfaces. Condensation will absorb into porous materials, such as gypsum wallboard and ceiling tiles, and elevate the material’s aw enough to allow mold to grow. Therefore, control of moisture in buildings, including hidden spaces such as exterior wall cavities, in both a liquid state and a vapor state, is critical to controlling mold growth in buildings.

To be continued…

Mold is an important part of the earth’s ecosystem, breaking down dead organic matter. For fungal growth to occur, four elements must be present: fungal spores, nutrient sources, appropriate temperature, and water. Of these four elements, water is the easiest to control in occupied buildings.

It is estimated that more than 1.5 million species of fungi exist. Fungal spores are ubiquitous; they are found in indoor and outdoor air, and on, and imbedded in, the surfaces of building materials. Non-HEPA (high-efficiency particulate air) filters, which are found in many building HVAC systems, cannot remove fungal spores from the air because of the spores’ very small size. These spores tend to disperse through the air and settle on all building surfaces, where they can remain dormant for years. It is impossible, or at best impractical, to remove fungal spores from the indoor environment.

Nutrient sources are any organic materials. The paper surface of gypsum wallboard is a prime nutrient, because it easily absorbs moisture. Even on inorganic materials, such as the vinyl in furniture, nutrients exist in settled surface dust. Such nutrient sources cannot be easily eliminated from the indoor environment.

The temperatures that are best for humans are also ideal for fungi. Different species of fungi have different optimal temperature ranges. However, in general, fungi grow well between 40 degrees Fahrenheit (4 degrees Celsius) and 100 degrees Fahrenheit (38 degrees Celsius). (Some can survive at temperatures down to approximately -23 degrees Fahrenheit [-30 degrees Celsius] or up to approximately 140 degrees Fahrenheit [60 degrees Celsius].) Because the comfort range for people is well within the comfort range for fungi, modifying temperature is not an option for controlling mold growth. 

To be continued…

The HVAC system is typically designed to control the temperature inside a building and, as a by-product, also may control relative humidity (RH). In addition to keeping most people comfortable, the HVAC system should also help control contaminants in three ways: by filtration (filtering contaminants out of the air before they reach the building occupants); by ventilation (diluting the contaminants in the air by adding fresh outside air); and by pressurization (maintaining the right pressure balances between building spaces to keep contaminants from moving into the wrong place). If the HVAC system fails to operate properly, IAQ problems usually occur.

Pathways involve both a route for contaminants to travel through a building and a mechanism like air pressure to push the contaminant along that route. Pathways are affected by the building design, the operation of the HVAC system, and the building use.

Building occupants who spend an extended period of time (an eight-hour work day, for example) in a building are likely to report symptoms when IAQ problems occur. They are a good barometer of the health of a building.

All four factors combine to create IAQ problems. A change in any one of them can cause a dramatic change in the types of problems and symptoms that occur.

A large office building in Los Angeles illustrates this interaction. Workers in one section of the building were exposed to chemicals, including paints and adhesives, from another section of the building that was being renovated. The fumes were migrating to the workers’ area through the HVAC system that served both areas. The workers sued the building owners and managers, as well as the contractors, product manufacturers, and installers, and won a large financial settlement. If the building owner or manager had been aware of the four IAQ factors and taken proactive measures, the problem could have been easily avoided. For example, the pathway or pressure that enabled the chemicals to reach the occupants could have been removed by setting up a temporary exhaust system in the renovation area and blocking the return vents to the building’s HVAC system. These simple steps would have prevented the chemical fumes from getting into the common HVAC system where they could travel to the occupied areas of the building.

To be continued….

Indoor air quality is influenced by a variety of factors, including outside air quality, weather, building operation, type of mechanical systems, existing contaminants, occupant types, and building. Buildings that are designed for one purpose often end up being used for something entirely different. The new use may be incompatible with the original building design, and if the building owners are unaware of the need to adjust the building or its operation to account for the new use, IAQ problems can result.

Most experts group all these interrelated influences into four primary factors that are common to every IAQ problem in every climate.

Contaminants that can result in IAQ problems are generally classified as:

• Combustion products (smoking and cooking)
• Volatile organic compounds (VOCs) from solvents and cleaning fluids
• Respiratory particulates (asbestos and dust)
• Respiratory by-products (carbon dioxide)
• Microbial organisms (fungi and bacteria)
• Radionuclides (radon)
• Odors (perfume, smoking, and mold)

These contaminants cause IAQ problems only when a specific set of conditions exists that promotes them or allows them to reach levels that cause reactions in susceptible building occupants. Sometimes these conditions can be changed easily and the problem quickly remedied. For example, simply increasing the volume or distribution of outside air may reduce elevated levels of VOCs within a building to acceptable levels. At other times, however, such as when microbial problems occur, the conditions can be complex, requiring modification of both the HVAC system and the building envelope along with careful removal of the microbially contaminated materials. In fact, in most cases, microbial problems only require a change in the environmental conditions for the problem to not return.

The major types of contaminants in a building depend on the building’s location and condition, the climate, and the building use. Moisture intrusion and mold are the number one problem in hot, humid, or rainy climates.

To be continued….