Q: We have just discovered a severe mold problem at our church. The church sanctuary is directly above a basement with a wet weather spring in it. The basement has not been used for years but we recently found that the mold has contaminated the sanctuary above. The air has been tested and it grew five colonies of mold. We have moved all meetings to another building and no one is allowed inside the sanctuary until we know exactly what we are dealing with regarding decontamination. We left everything inside the sanctuary including the piano, organ and hymnals. The building is over 40 years old. What is your advice on our best, most cost-effective, course of action?

A: Many aspects of the church construction impact how this situation should be handled, but the first step is to address the cause of the mold: the present moisture. Any remediation that is performed will be ineffective if the moisture level in the building remains high.

If the basement has a concrete floor, then the recommendation often is to dehumidify and perhaps add a sump pit/pump. Outside the foundation, French drains, foundation insulation and landscaping changes can limit water entry. Obviously, some options can be expensive and others are less so. Additional sources of moisture in a basement can be condensation from hot, humid air that collects on the cold surfaces that are in contact with the air. If the basement contains a dirt floor, then moisture may permeate the ground and enter the basement. A vapor barrier on the dirt floor can reduce this source of moisture. If moisture is leaching through the foundation wall (indicated by white powder called efflorescence, which is a salt), then sealing of the walls may be needed. Lowering the humidity in the basement is the ultimate goal, and there are a number of methods of accomplishing this.

Any porous material in the basement (such as cardboard) that is moldy should be discarded, and important papers should be stored in watertight plastic storage boxes. Books can be cleaned with HEPA filtered vacuums. The Northeast Document Conservation Center’s Web site (www.nedcc.org) is a good resource for information on document preservation. Non-porous materials such as sealed wood and plastic can be cleaned with disinfectant wipes that contain bleach.

The air sample you described with “five colonies” does not indicate a mold problem. Mold is in all air samples, except in a location such as an operating room. A professional analysis would describe the mold in either colony forming units per cubic meter or fungal structures per cubic meter. Air samples prior to remediation themselves are not nearly as useful as a good visual inspection and a tape or bulk sample of the affected building material. In general, 500 to 1,000 colony forming units per cubic meter would indicate a problem.

If visible mold is present on building materials, remediation often is needed. If the walls are plaster (not gypsum board) and the mold is from surface condensation, they can be disinfected. If water had entered the wall cavity or has been soaked up by gypsum board, you may be facing major remediation. An onsite inspection is required to determine what is significant growth versus a few deposited fungal spores. Interestingly, the ultimate reference for mold remediation in a church is found in Leviticus 14:33-59. A few things have changed, such as building materials, but the basic concepts are the same.

Thanks to Mark Goldman, who is a senior air quality scientist for Engineering and Fire Investigations (EFI), a firm that provides mold investigation and indoor air quality services nationwide. Mark can be reached at mark_goldman@efiglobal.com.

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If you have a question for a mold expert, please send it to Brett Lyon, senior editor of construction.com at brett_lyon@mcgraw-hill.com.