IICRC Updated WRT Exam Questions and Answers by bianka

The IICRC WRT body of knowledge defineshumidity ratioas theamount (or weight) of water vapor contained in a given weight of dry air. It is typically expressed as grains per pound (GPP) or grams per kilogram and represents an absolute measurement of moisture in the air.

Unlike relative humidity, humidity ratio does not change with temperature unless moisture is added or removed. This makes it one of the most reliable psychrometric measurements for evaluating drying potential and comparing indoor and outdoor air conditions.

The WRT manual emphasizes that humidity ratio is critical for determining vapor pressure, dew point, and the suitability of ventilation drying. Restorers frequently rely on humidity ratio to decide whether introducing outdoor air will improve or hinder drying.

Moisture content applies to materials, not air, and relative humidity is a percentage comparison rather than a mass measurement. Therefore, humidity ratio is the correct and precise term under WRT psychrometric science.

The IICRC WRT body of knowledge identifiesnon-penetrating (non-invasive) moisture metersas the preferredinitialmethod for surveying moisture in a wide range of building materials. These devices allow restorers to rapidly scan large surface areas without damaging finished materials, making them ideal for initial inspection and moisture mapping.

Non-invasive meters work by emitting electromagnetic signals that respond to changes in material density and moisture presence. While they do not provide precise moisture content values, they are effective at identifying areas of concern that warrant further investigation.

The WRT manual stresses that invasive meters, material removal, or drilling should only be performedafternon-invasive methods indicate elevated readings and when confirmation is required. This tiered approach minimizes unnecessary damage while still ensuring accurate assessment.

Additionally, non-invasive meters are particularly useful on surfaces like ceramic tile or plaster, where penetrating probes may be impractical or destructive. Proper documentation requires that readings be repeatable and defensible, and starting with non-invasive tools supports both goals.

The IICRC WRT body of knowledge explains that when outdoor air has alower humidity ratiothan indoor air, ventilation can be used to reduce the indoor humidity ratio by replacing moist air with drier outside air. This reduction directly supports evaporation and drying.

Ventilation works by exchanging air masses. If the incoming air contains less moisture per pound of dry air, the overall moisture content of the drying chamber decreases. The WRT manual stresses that psychrometric comparison—not temperature or relative humidity alone—must be used to determine whether outdoor air is suitable.

Ventilation does not directly reduce microbial growth; rather, it reduces moisture conditions that support microbial amplification. Static electricity and sublimation are unrelated to ventilation drying.

Properly applied ventilation is recognized by the WRT standard as a legitimate moisture removal method when conditions allow, though it must be monitored to ensure effectiveness and prevent unintended moisture introduction.

According to the IICRC WRT body of knowledge, theinitial dehumidification capacity recommendationis determined by three primary factors:cubic footage of the affected area,class of water intrusion, andtype of dehumidifierbeing used. This calculation establishes a baseline moisture removal capability required to manage the anticipated evaporation load.

Cubic footage defines the volume of air within the drying chamber and directly influences how much moisture must be removed from the environment. Theclass of waterdescribes how much moisture has been absorbed by materials and the rate of evaporation expected. Higher classes (Class 3 and 4) require substantially more dehumidification capacity due to increased moisture loading and deeply absorbed water.

Thetype of dehumidifieris equally critical because different technologies (conventional refrigerant, LGR, desiccant) have vastly different operating ranges, efficiencies, and moisture removal characteristics. The WRT manual specifically differentiates capacity calculations for LGR versus desiccant systems, as they function under different psychrometric conditions.

Factors such as category of water, subfloor type, or air mover quantity influenceprocedural decisions, safety, and drying strategy—but they are not part of the initial capacity calculation. Likewise, grain depression is a performance outcome used for evaluation, not an input variable.

This structured approach ensures consistency, defensibility, and alignment with the ANSI/IICRC S500 Standard, enabling restorers to justify equipment placement using measurable, science-based criteria rather than guesswork or habit.