Technical Updates

Posts Tagged ‘rainwater intrusion’

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…

These blog posts are brief by design and are not intended to provide comprehensive engineering data available elsewhere, nor to substitute for professional expertise. Instead, they address key issues and  help owners, designers, and contractors work together to improve decision-making. This is especially needed as architects participate in more construction work (e.g., through design/build) and as builders provide more preconstruction services.

No single piece can address all the issues related to moisture intrusion and mold growth. However, we believe that this blog addresses a significant proportion of the problems that architects will encounter in the design and construction of a typical commercial building. Nevertheless, the design and construction team are advised to seek additional input from other documents as well, and there are a variety of readily available, technically sound resources.

While this blog is intended primarily for commercial construction, the fundamental issues are similar, if not identical, in residential construction and can be dealt with in a similar fashion. However, the scope of these posts remains targeted to commercial architecture.

Most of the information presented here relates to preventing moisture intrusion and mold problems in hot, humid, or rainy climates, which is a significant portion of the United States. Parts of this blog address other regions and climates (for example, cold climates), but not in significant detail. For technical information on issues related to design and construction in those climates, please refer to other publications.

The majority of our blog content relates to air- or vapor-borne moisture. Mold and moisture problems associated with plumbing leaks or groundwater intrusion are not included. In our experience, those problems are usually more easily identified and resolved. While rainwater and groundwater intrusion are briefly mentioned in this blog, readers would be advised to seek additional information in resources specializing in those issues.

Today, there is unquestionably more information about the causes of and solutions for moisture and mold problems. We hope we have converted this information into usable knowledge that can be applied to create problem-free buildings.

To be continued….