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Secondary Water Damages after the Storm

The tallies of Harvey's damage are becoming more clear. Harvey is being blamed for an unprecedented amount of destruction of property. While some areas remain flooded almost all are now above water which means folks are now tallying their loses. More than 200,000 homes have been flooded, destroying hundreds of thousands of personal possessions. Millions of memories are sitting on curbside or on their way to the landfill.

FEMA has issued guidelines for curbside disposal. Some appliance components will be recycled. Damaged refrigerators, freezers, air conditioners will likely fill multiple football sized storage area waiting for the Freon to be captured so it doesn't leak out into the environment causing consequential damage to the ozone layer. You can access FEMA's guidelines for disposal at this link: .

Drywall Removal

In their "Tips for Clean-up" FEMA has stated: "Remove all drywall and insulation that has been in contact with flood waters".

While this is an important step, it has been my experience that in many cases this may not be adequate. Drywall and insulation are porous materials that are subject to capillary action. When low humidity levels are present in the air water can still rise in gypsum drywall at a rate of about one-half to one inch per hour. In a wet humid condition such as after a flood the rise can be many times faster. If gypsum wallboard remained in standing water for 24 hours, the level of wet gypsum could easily extend a couple of feet higher than the high water mark. Very commonly the water will travel upward to a point where it hits a capillary break. When the material is installed horizontally the flood water will commonly raise in the gypsum to the joint that is four feet up. If the wallboard is installed vertically or the flood waters rise above four feet, the gypsum will commonly be wet all the way up to the ceiling.

When removing gypsum drywall without specialized cutting tools that make a straight cut easy, you can often work much quicker by removing the full sheets at the joint compound mark 4 feet up. Once you start peeling away the joint compound at the joint tape it will usually become apparent where the seam between the sheets of gypsum is located. Not only does the wallboard come off quicker and easier if you don't have to cut it, but it will also be removed at the correct height to make full sheet re-installation easy. Don't install new gypsum wallboard until you know the wood framing is dry enough as measured by a moisture meter. Damp wood will have sufficient moisture to cause the brand new gypsum to develop mold. You can't tell if wood is dry with your hand. Even if it feels dry - it may not be.

Issues with Installing Drywall

In 2005 Hurricane Wilma hit Key West Florida with a storm surge that swamped 80% of the island. I was there two weeks later. By the time I arrived most of the wet gypsum wallboard, insulation carpet and other debris had been hauled away. If you didn't know the island had flooded most people wouldn't be able to tell by looking that the island's homes had suffered major damage. Some homeowners had already reinstalled new insulation and wallboard over the wood framing that felt dry to the touch. I had been brought into Key West by my client because many of the brand new materials that were only a few days old were beginning to grow mold and had a strong musty odor.

My moisture meters and thermal imaging camera told the story. Wood framing had absorbed water and remained elevated - especially where it was in contact with concrete slab floors. In some cases the wood moisture content was over 25%, but it felt dry to the touch. The wood was dry at its surface but was still very wet a few millimeters deeper into the wood. The paper on gypsum wallboard when in contact with the wood created an environment where the residual moisture migrated through the wood into the gypsum paper where it was nailed to the stud framing. Mold can start to grow in the adjacent gypsum paper if the wood has somewhere between 16 & 17% moisture content. The science behind these materials shows that paper is about twenty times more likely to develop mold than the wood framing. Air movement can help prevent mold from growing on exposed surfaces of framing, but if the humidity isn't reduced significantly the wood won't dry.

Secondary Water Damage

Another issue that needs to be addressed on a case by case basis is what materials need to be removed and discarded based on secondary damage. This is the damage caused to materials that don't get physically wet from liquid water or capillary action, but instead from elevated levels of relative humidity. If ceilings are sagging or are found to be wet when tested with a moisture meter, they should also be removed and discarded since the cavities behind these materials will frequently develop hidden mold growth even if it doesn't show up on the surfaces.

Because water can travel through capillary action and also through high humidity it is critical for folks to make every efforts to thoroughly dry all materials that will not be discarded. Please help me spread the word to those who will find this information useful by sharing this post. Thank you.


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