A moisture test measures the amount of water in the structure of a house, and it helps identify water damage within the framework of the house. Usually, wood for construction has a moisture content of 19 percent. Moisture above this level can cause the wood to warp or shrink after installation. As the wood dries, the moisture level settles between seven and 13 percent. The moisture test is typically conducted at an exterior wall and consists of a moisture meter and a probe.

Usually, a visual examination of the house will reveal potential areas of water damage. Once an area is suspected of excess moisture, a moisture test is conducted. There are several different methods to measure the water content in a structure.

An exterior probe test begins when an inspector drills two holes into the siding. He inserts test probes into the holes until they make contact with the sheathing, and takes a measurement. Then he fills the holes with caulk afterward. Exterior probe testing is beneficial because the inspector can make a damage assessment regarding the sheathing, while conducting the moisture test.

A moisture test via the interior probe method is usually done when a home isn't accessible to the exterior probe method. An interior probe test accesses the sheathing by penetrating the sheetrock and vapor barrier through two small holes. Probes are inserted into the holes and a measurement is taken at the sheathing. The holes are filled with spackle compound afterward.

Another way to detect the moisture in a structure is through radioscopic scanning. This method is usually applicable for vinyl or wood and is usually done to locate potential areas of moisture. A scanner is used to determine the density of the material within the wall. It is only a preliminary test, which is usually followed by probe testing to measure the moisture content.

Infrared photography is another tool used by home inspectors to determine the amount of moisture in the house. It identifies areas within the walls, roof, or ceiling that have a different temperature than the surrounding areas. A temperature difference in the structure may indicate the presence of moisture, but it is not always accurate. It doesn't determine the actual moisture content either.

A bore scope is another tool used by inspectors to check for moisture. It provides a small viewing area to examine the interior wall cavity to determine the extent of water damage. Signs of rot are followed up with probe testing.