Q: Last May I fixed a very bad, but short-lived, leak in the roof my house here in eastern Pennsylvania. The leak was bad enough that water made its way through the roof and ceiling and into walls two floors below. My house is about 75 years old. Four months later I can neither see nor smell any sign of mold. Are molds always detectable by casual inspection or should I hire a professional to inspect my home? Are there self-testing kits on the market and if so, how effective are those compared to professional services?

A: Mold is not always detectable by casual inspection. Mold growth can occur inside wall and ceiling cavities that are hidden from view. Porous, cellulose-based building materials can support mold growth if they have become saturated with water as would be the case with the roof leak you describe. To support mold growth you need a suitable substrate and environmental conditions conducive to growth.

Plaster walls and ceilings typically do not support mold growth while gypsum board, under the right environmental conditions, does. Wood framing, sheathing and some insulating materials can also support mold growth.

I personally do not know of any self-testing kits on the market. If you are concerned about the potential presence of mold in your residence, or if you or someone else living in your home has asthma or any other condition that may compromise the respiratory system, you should hire a professional to inspect your home for the presence of mold.

Mary Biagotti is a certified industrial hygenist with EFI Global's Boston office. EFI Global is a full-service engineering, environmental and fire investigations firm serving commercial, industrial, institutional and government entities.

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