After a flood, the normal response is to clean up and rebuild as soon as possible.

“However, rebuilding too quickly after a flood can cause continuing problems such as mold growth and deterioration of wood and wall coverings,” warns Ken Hellevang, North Dakota State University Extension Service agricultural engineer and flooding expert.

The NDSU Extension Service’s flood Web site, http://www.ag.ndsu.edu/disaster/flood.html, provides information on flood recovery, including a video on restoring flooded buildings and fact sheets on topics such as cleaning your flooded or water-damaged home and drying out before rebuilding.

Also, most county NDSU Extension Service offices have moisture meters that people can borrow to determine if they adequately dried the parts of their homes and other buildings that flooded before they start rebuilding. Typically, the counties charge a $100 deposit, which is refunded when the meter is returned.

Hellevang says one important thing for people to remember is that cleanup, including removing all porous materials (such as carpet, drywall, fabric and ceiling tile), cleaning all nonporous materials (such as metal and glass) and thorough drying, should be done soon, but rebuilding needs to be delayed until moisture is no longer coming through concrete in the basement and wood has dried to at least 15 percent moisture content. Wood submerged in water will absorb a large amount of water, so drying will take weeks.

A common problem with rebuilding too quickly is mold growth within closed cavities, such as on the back of drywall (Sheetrock). Mold can trigger allergic reactions, asthma episodes and other respiratory problems.

Air moves from within the wall cavity into the living space, so mold growth in the wall will affect the living space. Air also will move from basements and crawl spaces into the living space, so mold in these areas will affect people living in the home. Living in an environment that contains mold is not healthy.

Building materials may be wet even though they appear dry on the surface, so checking the moisture content by using a moisture meter before rebuilding is important, Hellevang says.

Wood moisture content should be at or below 15 percent to minimize the potential for mold growth. Wood may not decay until exceeding a moisture content of about 20 percent, but mold growth is expected in wall cavities that contain wet wood.

Meters calibrated for measuring wood moisture content also can provide a relative moisture measurement of other materials such as drywall. However, the meters only measure moisture content; they do not determine if mold is present. Meters are not available to detect mold growth.

Testing for mold requires sampling by a trained professional with special equipment and evaluation by a technician with training in mold identification. It’s also very expensive. Test kits purchased from local stores or off the Internet do not provide accurate information.

“Focus on removing wet materials and drying the structure,” Hellevang advises.

If mold is visible or you detect a musty smell, remove the moldy material using accepted procedures such as described in NDSU publication “Remove Mold for a Healthy Home.” It’s available online at http://www.ag.ndsu.edu/pubs/yf/home/ae1202w.htm.

Hellevang also recommends checking for moisture coming through the basement’s concrete walls and floor by taping a 3- by 3-foot plastic sheet to the floor or wall and watching for moisture accumulating behind the plastic during a period of a few days. The soil surrounding a flooded home may take weeks or months to dry adequately to permit rebuilding.

NDSU Agriculture Communication