Technical Updates

Posts Tagged ‘mold and moisture problems’

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…

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….

An alarming number of new buildings suffer from moisture and mold problems. The risk of failure is highest in (but not limited to) cold, temperate, hot, and humid climates. The debate on why some buildings fail and others do not, who is responsible for these failures, and how to fix them rages on. But instead of being aired in architecture schools and at engineering society meetings, this debate goes on in courtrooms and mediation hearings among highly paid expert witnesses and lawyers – not among people who should prevent failures but among those who are rewarded by their occurrence.

The building industry seems baffled about the prevalence of building failures. Many wonder why the rate of building failures is not declining despite better technology, increased training, and more sophisticated building systems. It is not from indifference or ignorance. We know we can prevent buildings from failing because we can fix them once they do fail. The reason we are not coming to grips with this problem is simple: the design professionals entrusted with how buildings perform are not receiving adequate feedback on the performance of their previous buildings.

Without that feedback we do not know why some buildings work well and others do not, despite their being apparently designed the same way. Metrics may say that we did a good job, yet clients keep complaining about building failure, and the construction litigation business keeps growing. Until architects and engineers receive better performance feedback, they will have neither the ability nor the incentive to change.

To be continued….