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Mold in Buildings

The problem of mold in buildings is one that no building owner or manager can afford to ignore. Mold has been suggested as one of the possible factors in so-called “Sick Building Syndrome.” Throughout the country, deaths of infants from pulmonary hemosiderosis (bleeding lung disease) have been attributed to inhalation of toxins produced by the fungus Stachybotrys chartarum.

The U.S. Department of Housing and Urban Development awarded $3.1 million to the city of Cleveland to remediate mold and moisture problems in houses and apartments. Mold problems in the Martin County Courthouse in Florida apparently caused by a leaky EIFS façade cost $26 million to remediate. The building cost $13 million to construct a few years earlier.

Criterium Engineers was asked to investigate a mold problem in a relatively new office building that was undergoing extensive renovation. The contractor encountered wet and moldy insulation and gypsum board during demolition. We were able to determine that the cause of the mold problem was water intrusion. The head flashing over the windows had been installed upside down so that water was channeled into the wall cavity rather than away from it. Excess mortar in the wall cavity (mortar bridging) prevented air from circulating within the cavity and drying it out and also formed a path for water to travel from the inside of the brick veneer to the surface of the gypsum board. Because of blocked weep holes there was no path for water to drain away from the wall cavity. The cost to remediate was estimated at nearly $180,000.

What is mold? What does it need?

The words mold and mildew are sometimes used interchangeably to refer to the same thing. Mold is the growth produced by several types of fungi as they feed on organic matter. There are thousands of types of fungi not all of which are harmful. Some types of fungi are beneficial such as those used to produce Camembert and Roquefort cheeses. The drug penicillin is a by-product of the fungus Penicillium notatum.

Mold typically reproduces asexually by means of airborne spores. These spores are always present in the air. The spores need only the right conditions to take hold: water, food, and the right temperature range. Mold also grows better in a dark environment, such as behind walls or in HVAC ducts.

Buildings can provide an almost ideal environment to support the growth of mold. The typical temperature in buildings is optimal, there are plenty of dark places, and there are plenty of organic substances for mold to feed on. Just add water and you’ve created a perfect mold breeding ground.

Why is mold harmful?

Mold can be harmful for two reasons. First, mold can feed on and destroy most of the organic materials found in buildings, such as wood, paper, carpet, and glue. Almost any surface can support the growth of mold.

Second, mold can cause harmful health effects. Although the species Stachybotrys chartarum has received most of the press, many other types of fungi are potentially harmful to humans. For this reason, Stachybotrys chartarum is not treated as a unique case.

Exposure to fungus can cause organic dust toxics syndrome (ODTS) or hypersensitivity pneumonitis (HP). ODTS may occur following a single exposure to high concentrations of dust contaminated by fungus as might be encountered during remediation or renovation work. The symptoms are flu like. HP occurs as a result of prolonged exposure and can lead to permanent lung damage. Exposure to fungus can also cause allergic reactions: typically a runny nose, sneezing, eye irritation, cough, or aggravation of asthma.

How are mold problems detected? Because mold is not only a problem in itself but also a symptom of a water problem the first step in any investigation for the presence of mold in buildings is to follow the water. Any damp or wet areas are suspect. Look for evidence of high humidity, condensation, or visual evidence of water staining. Other visual clues are the direct observation of mold. Because mold grows in dark, hidden places and may not always be visible, check for other clues such as musty odors or reported physical symptoms in occupants.

Testing, in order to identify the particular species of mold, can be performed by a number of laboratories. The EPA has recently developed a DNA-based testing procedure that dramatically reduces the time it takes to identify which one of the 100 or so most common mold species may be present. Using this technology, tests that used to take days or weeks can now be performed in a matter of hours. Information on the EPA testing method is available at http://www.epa.gov.

What to do if you have a mold problem

As we have noted, buildings can readily supply the conditions that mold needs to flourish; namely, a favorable temperature range, food, and water. Since mold likes the same temperatures as humans, changing the ambient temperature as a method of control is usually ineffective. It is hard to eliminate mold’s food supply entirely because it feeds on a wide range of materials commonly used in building construction and interior finishes. However, since mold can feed on dirt, cleanliness can go a long way towards control.

The easiest way to control mold growth is to eliminate the source of water. Moisture in a building can exist in two forms: as humidity and as free water. Moisture may come from the inside of the building through condensation, plumbing leaks, cooking, showers, or the HVAC system. Water may enter the building from the outside through leaks in the roof, the façade, or the basement. Water may also be introduced through the use of wet building materials such as roofing materials, insulation, and gypsum board.

For help with mold problems, contact an engineer qualified to perform the diagnostics necessary to determine the root cause of the problem. Determining the presence of mold is relatively easy. Determining the cause of the problem is often a complex process involving detective work. There are often false leads. Inexperienced people often mistake effect for cause, leading to a misdiagnosis. The potential liability of what may appear to be a relatively simple and straightforward mold problem is too great to risk retaining the services of anyone other than a competent professional.

Remediation usually involves eliminating moisture

Any plan to remediate mold must first address solving the water problem. The source of the moisture must be identified and the condition rectified. Only then should the process of remediation begin. Remediation consists of either cleaning the affected materials in place or the removal and replacement of these materials. The decision of whether to clean or replace is largely an economic one based on the size of the areas affected, the ease of access, and whether or not the building components have been damaged by either the mold or water.

Small areas can be remediated by maintenance staff; larger areas by trained contractors. The New York City Department of Health publishes a document titled “Guidelines on Assessment and Remediation of Fungi in Indoor Environments.” It may be helpful and is available on-line at “http://www.ci.nyc.us/html/doh/html/epi/moldrprt1/html.

At least one company treats moldy houses by enclosing them and raising the interior temperature in a controlled manner to about 160°F. This effectively bakes the mold and kills it.

Volume 12, Number 3

July 2001

Copyright © 2001

The Engineering Advisor is intended to enhance your knowledge of technical issues relating to buildings.  For additional information on any subject, please feel free to call us.  Our commitment is to provide you with timely, accurate information.