In my post for What's Involved in Mold Remediation I promised to bring you an article about making drying decisions. In order to discuss drying let's first suppose that removal of unrecoverable wet building materials is complete. Also, demolition should be complete and ruined materials are on their way to the landfill. Let's also assume that aggressive removal of mold from wood and other surfaces that are going to remain in the building (concrete, masonry, exterior siding ...) is complete. Additionally, assume that bacterial contamination has been flushed from under sills and other surfaces. Even with all of these steps, the home is still not quite ready for reconstruction. Once the finish materials are reinstalled you will no longer have access to the wall cavities or other spaces that become hidden - so please spend the additional time and effort to make sure everything is dry!
Two Critical Checklist Items
There are two items on this checklist that are critical and will help you with the rest of the checklist.
If you are going to be doing any part of the reconstruction after flooding, you must have a moisture meter an know how to use it.
If you are going to hire a contractor to do the reconstruction they must have a moisture meter and know how to use it.
Checklist for Drying a Home
Make sure the building is completely dry using moisture meters to confirm the building is dry. I have run into contractors claiming that if the moisture content of the wood is reduced to 19%, the building is dry. This is not true. 19% is low enough to prevent wet rot and dry rot from causing decay in the wood portions of the structure, but it is more than enough moisture to promote mold growth on sensitive interior finishing materials.
The average wood moisture content in the United States is 10%. Humid environments will have a higher moisture content but it should never go above 16% or molds can start to grow. Ideally soft wood in humid environments will be 12% to 14% wood moisture content. Since moisture meters only provide an approximation of the moisture residues that are present, it is better to error on the side of caution. Twelve percent moisture content for wood in a humid climate is ideal.
Since every moisture meter measures differently - it is important to understand how the meter you are using works. Read the manufacturers instructions. Some meters have sharp probes that are inserted into the wood. Other meters use a electronic signal (either conductivity or radio frequency) to determine if materials are dry. Most meters only measure as deep as the probe is inserted or to a maximum depth of 0.5 inches.
Establish a "dry standard" for each type of material you are checking for each meter you are using. Since different meters measure differently - you may not be able to compare readings collected with different meters. Ideally the same meter would be used to monitor trends. Find a representative material that you know is dry.
Do this for each different type of material that is remaining in your home. The measurement for different types of woods will also vary so check the differences for framing and flooring that will remain. If there is no area of your home that remained dry, you may need to check the same type of material in a neighbor's home that didn't flood.
Moisture meters can not be used for determining if materials under metal flashing, metal framing, or other material that conduct electricity are dry. Conductive materials will always measure wet.
Some types of chemical wood treatment will also thwart the moisture meters since salts or other chemicals can conduct electricity.
Wood doesn't necessarily dry evenly. Mold doesn't care how wet the wood is in the center only at the surface. The wood may feel dry at the surface, but be wet deeper in the material; however, over time that moisture will migrate to the surface where it can result in mold growth. This is especially true if gypsum wallboard with paper is in contact with the damp wood. Paper on gypsum wallboard is twenty times more likely to develop mold than the wood framing.
Since most meters are only able to measure about 0.5 inches into a material, they may not be able to determine if materials are dry at a deeper level. There are specialty penetrating meters that have long insulated probes that can be driven deeply into wood materials to be sure they are dry all the way through.
If you are in doubt it is best to have your home certified dry by an ICRA, IICRC or RIA firm (see my September 5, 2017 post).