Testing Tools and an Evaluation of Common Testing Methods

Understanding Moisture Levels

Moisture levels in the wood could be determined by weighing your home before and after it's dried. The difference in weight is the percentage of moisture in the wood. Instead of weighing your home, CMT inspectors probe the wood and measure the moisture content with electric resistive testing meters—protimeters.

The American Wood Institute says that typical construction woods (SPF’s) should be dried to at least 19 percent moisture content before being used in construction. 

Wood must meet this specification in order to:

1. Prevent significant shrinkage of framing members as they continue to dry.
   
   
2. Minimize warping as the wood continues to dry.
   
   
3. Prevent or minimize mold growth on wet wood (see mold facts).
   

The woods used in construction will continue to dry after a home is built, roofed, and cladded. Most homes that do not have water intrusion problems have moisture contents between 7 to 13 percent in the wood structure of the home. A moisture level above 13 percent may indicate that moisture is being introduced into the home. Because many factors go into determining whether a moisture reading is significant or not, detailed testing and analysis is needed to verify suspected moisture problems.

 

Common Moisture Testing Methods

Exterior Probe Testing can be used to test all homes except those built with brick. Two small holes (3/16” in diameter and about one inch apart, like a small snake bite) are drilled through the siding only. Test probes are inserted into the sheathing, behind the siding, to measure the moisture content and check for damage. After the test is complete, the holes are sealed with color-matching caulk. 

Exterior Probe Testing is the preferred method used at CMT
because we know that:

1. Most moisture found in a home is caught between the sheathing and the cladding of the home on the exterior side of the wall cavity.
   
   
2. Testing the exterior of a home allows the inspector to test all areas where moisture is found without being limited by framing members, floors, ceilings, furniture, and other items that can get in the way.
   
   
3. Exterior testing allows inspectors to seal the test holes with color-matching caulk that virtually conceals the test holes. The test holes do not harm
   the home or cause new sources of moisture entry.
   
   
4. Exterior testing does not breach the vapor barrier on the internal
   side of the wall cavity.
   
   
5. Exterior testing allows the inspector to determine the condition of the sheathing, which is necessary to make a damage assessment. Damage assessment is an integral part of the moisture test and is critical to filing a claim. A damage assessment is also needed to accurately determine the amount of remediation that may be needed on the home.
   
   

Other Testing Methods

Interior Probe Testing is used by CMT to test brick and areas of a home that are not accessible to exterior testing. Two small holes (1/8” in diameter and about one inch apart, like a small snake bite) are punched through the sheetrock and vapor barrier. Test probes are inserted into the sheathing, through the six-inch wall depth, to measure the moisture content. After the test is complete, the probe holes are sealed with a spackle compound. Damage assessment is often difficult to conclude with interior testing.

Radioscopic Scanning is used by CMT on vinyl, wood, and EIFS to indicate areas where moisture maybe present. A wet wall scanner does not measure moisture levels; instead it senses areas of moisture. Probe testing in indicated areas is necessary to measure moisture and assess possible damage. 

A scanner works by reading the density, not moisture, of the material found in the wall cavity. A scanner may offer incorrect readings because electrical, plumbing, HVAC systems, cementious-based products, metal lathes. Be cautious of inspectors who use scanners to moisture test stucco applications. Scanning traditional stucco just doesn’t work.

Infrared Photography can be used to show areas where a temperature difference exists in a wall, roof, ceiling, or attic area. This method is often used as a non-invasive tool, to show where moisture intrusion has occurred. However, its use should be limited because it only shows temperature variances, not moisture levels, that could also be due to sunlight, wind, shade, lack of insulation, or air leaks. Our experience indicates that infrared photography only shows moisture intrusion 25% of the time and does not assess damage or dry rot. The other 75% of moisture issues go unnoticed. For this reason, some home sellers, builders, insurance adjusters, and realtors request infrared inspections because they don't want to find moisture problems. Even when infrared testing is used, probe testing is still necessary to measure the moisture level and assess the damage to wood in the wall cavity. Be cautious of inspectors who rely exclusively on infrared photography for moisture testing. This method should only be used as a verification tool.

Bore scopes are a tool used to look (peek) inside the wall cavity. This verification tool has a limited capacity because its viewing area is very small, which means that assessing water damage is difficult. Again, probe testing is the only way to accurately measure moisture levels. Be cautious of inspectors who use borescopes inserted into the wall at an electrical outlet boxes. This is because most outlets are in areas where moisture intrusion issues are not typically found.

Visual inspection is a necessary part of every moisture test. A qualified inspector knows where roof flashing is needed to keep a home dry, where caulking should and should not be applied, and knows the signs of moisture and where moisture issues occur. A visual inspection will help identify where problems may exist. Probe testing is still required to accurately measure moisture levels.

Many times stains are present on the exterior cladding. CMT's experience has shown that approximately 50 percent of the time stains do not mean moisture intrusion is occurring. However, stains need to be probe tested because moisture intrusion in the wall cavity is not visible.

The Bottom Line: Probing the wood strucutre of your home is the only way to accurately measure and assess moisture levels and damage. CMT inspectors always use the least invasive method to accurately measure moisture levels and assess damages.