When it comes to construction, determining the correct moisture content of wetted building materials and analyzing corresponding locations, orientations and patterns is of imminent value to forensic engineers and building scientists. As many building damages relate to insurance claims and construction defect/ subrogation lawsuits, legal challenges to the accuracy of measured moisture content (MC) have arisen.
Moisture in the built environment
Various types of leaks may expose the built environment to a range of potential MC. A common roof or window leak causes low-volume moisture intrusion that subjects the interior building components to an intermittent source and corresponding elevated MC, while a sudden plumbing leak may result in near saturated conditions.
Gypsum board drywall and wood building products are near universal in modern construction. Extended moisture exposure to interior building components causes fungal growth, deterioration, and eventual weakening and/or failure of the material.
A wide range of possible moisture contents within a building subjected to a leak prompts the question as to the precision of moisture meters at a range of contents, substrates, and which meter is more effective under which specific circumstance.
Study materials and methods
An independent study was conducted to establish the level of precision of common moisture meters used to quantify and measure moisture content in building components. The study tested four different brand moisture meters in gypsum and wood substrates at normal, high and saturated moisture contents. After specified periods of wetting, four different brands of moisture meter were utilized to determine the moisture content of specimens by manual pin type measurements. The results were compared against laboratory-obtained moisture content to assess the accuracy of meters in each substrate at a varying range of MC.
- Meter E had a retail price of $320.
- Meter G had a retail price of $35.
- Meter S had a retail price of $599.
- Meter T had a retail price of $342.
A moisture meter used to determine dampness levels in a concrete wall. (Photo: Shutterstock)
Different brand meters are designed to be accurate within varying ranges of moisture content. Moisture meters should be used within their manufacturer specified range of moisture content. Values obtained outside of this range may not be accurate.
- All meters functioned well at low moisture content, within a very narrow margin of error.
- All meters functioned well in moderately wet conditions, within a two to six percent margin of error.
- Meter T was the most accurate meter over the entire range of moisture contents, and generally followed the general trend of laboratory obtained MC. As Meter T had the longest pins, pin length may have enabled more accurate measurements.
- In low moisture content, Meter G functioned precisely; at a 0.28% deviation from laboratory obtained MC.
- Meters G and S exhibited a reasonable margin of error at a high moisture content.
- Meter E was not accurate at high moisture content.
All meters functioned well at low moisture content within a very narrow margin of error. Due to variations in material characteristics, meters exhibit some level of inherent inaccuracy in composite materials such as modern gypsum board (drywall). Think of drywall as a paper and gypsum sandwich with gypsum in the middle.
Consequently, in moderately wet and saturated conditions, meters may have overestimated the precise MC by measuring the saturation in the outer paper facing and not registering the precise MC in the gypsum core.
In moderately wet and saturated conditions, Meter T may have undergone a random error as it failed to detect wet conditions and five of the six measurements were the same numerical value. Such an error represents the need to verify calibration of the meter after purchase and on a regular basis during use. Currently, Meter S is the only meter that comes stock with an electrode to verify accurate calibration.
Ironically, Meter G (least expensive) and Meter S (most expensive) followed the same exact trend, returning 100% wet values in moderately wet and saturated conditions, which were not correct moisture contents, but were both satisfactory in detecting wet conditions. It is also apparent from this data that price may not be the best indicator of measurement accuracy.
These findings are valuable for claims professionals, engineers and others who are trying to determine the scope of damage following a water damage event. Knowing what types of meters provide the most accurate readings enables those conducting inspections to choose the best tools for their toolbox.
Abel Crean (firstname.lastname@example.org) is a forensic engineer in the greater Miami area for GeoHazards, Inc. He has performed research on ultra-high-performance concrete, infrared thermography, and moisture in the built environment.