How Structural Drying Works

Psychrometry is the science behind everything a restoration technician does. In simple terms, it describes the relationship between temperature, humidity, and the air's ability to absorb moisture. Understanding this relationship is what separates professional structural drying from the homeowner approach of “open the windows and run a fan.”

Here is the core concept: air has a limited capacity to hold moisture, and that capacity increases with temperature. Warm air can hold far more water vapor than cool air. When air reaches its maximum capacity, we call that 100% relative humidity—the air is fully saturated. The goal of structural drying is to keep the air around wet materials at a low relative humidity (ideally 40% to 50%) so that moisture is constantly being pulled out of the building materials and into the air, where dehumidifiers can capture it.

Technicians use a tool called a psychrometric chart (or increasingly, a digital hygrometer and drying software) to calculate exactly how much moisture the air can absorb at any given temperature and humidity level. They use this data to position equipment, adjust settings, and make daily decisions about whether drying is progressing on schedule. A reading that shows 80% relative humidity in a drying zone tells them they need more dehumidification capacity. A reading at 35% tells them the system is working efficiently.

LGR dehumidifiers (low-grain refrigerant) are the workhorses of structural drying. These commercial units stand about three feet tall, weigh 100 to 150 pounds, and can remove 15 to 20 gallons of water from the air every 24 hours. They work by drawing humid air over refrigerated coils, causing the moisture to condense and drain into a collection tank or pump out through a hose to a sink or drain. The “low-grain” designation means they are engineered to keep pulling moisture even when humidity levels drop below what standard dehumidifiers can handle.

Air movers (sometimes called blowers or fans) serve a different purpose than you might think. They are not there to “blow things dry” the way a hair dryer works. Instead, they create high-velocity airflow across wet surfaces, which accelerates evaporation by constantly replacing the thin layer of saturated air sitting directly on the material with drier air. Technicians angle them strategically—pointed at walls from 6 to 12 inches away, across flooring, and into wall cavities through flood cuts. A typical water loss requires one air mover per 10 to 16 linear feet of affected wall.

HEPA air scrubbers filter the air continuously during the drying process. They pull air through a High Efficiency Particulate Air filter that captures 99.97% of particles at 0.3 microns—including mold spores, bacteria, dust from demolition, and fine debris. This protects both the occupants and the technicians, and prevents cross-contamination to unaffected areas of the home. Air scrubbers also create negative air pressure in the drying zone, which prevents contaminated air from migrating to clean areas.

Desiccant dehumidifiers are used in specialized situations where LGR units are less effective—primarily in cold environments or where extremely low humidity levels are needed. Instead of refrigerated coils, desiccant units use a chemical drying agent (similar to the silica gel packets in shoe boxes) to absorb moisture from the air. They are common in crawl spaces, attics, and during winter drying jobs. At WaterTite, we deploy our Phoenix D385 desiccant dehumidifier for exactly these scenarios.

The IICRC S500 is the nationally recognized standard for professional water damage restoration. Published by the Institute of Inspection, Cleaning and Restoration Certification, it establishes the procedures, equipment requirements, and documentation standards that restoration companies should follow. When your insurance company evaluates a restoration claim, they compare the work performed against this standard.

The S500 defines four classes of water damage based on the rate of evaporation needed, which determines how much drying equipment is required. Class 1 involves a small area with minimal absorption—think a portion of one room with water on hard flooring only. Class 4, at the other extreme, involves deeply saturated materials like hardwood, plaster, or concrete that require specialty drying techniques. Each class has specific equipment-to-area ratios that tell technicians exactly how many dehumidifiers and air movers are needed.

Following the S500 is not optional for reputable companies. It protects you in two critical ways: first, it ensures your home is dried properly according to proven scientific standards, not guesswork. Second, it creates the documentation trail your insurance company requires to approve the claim. If your restoration company cannot cite the S500 class and category of your loss, that is a red flag.

Structural drying is not a “set it and forget it” process. A technician visits the job site daily—sometimes twice daily for complex losses—to take moisture readings, check equipment operation, and adjust the drying plan based on actual progress. This monitoring is one of the most important aspects of the entire process, and it is what separates professional restoration from dropping off equipment and hoping for the best.

Each day, the technician uses pin-type and pinless moisture meters to check readings at dozens of predetermined points throughout the affected area. These readings are recorded in a moisture map—a detailed document that shows exactly where moisture levels stand at every monitoring point, compared to the baseline readings from day one and the dry standard targets. Atmospheric readings (temperature, relative humidity, dew point, and grains per pound) are also recorded to verify that the drying environment is performing properly.

This data creates what the industry calls a “drying curve”—a graph showing how moisture levels are declining over time. A healthy drying curve shows steady, predictable decreases. If the curve flattens or reverses (moisture going up instead of down), it tells the technician something has changed: equipment may have malfunctioned, a secondary water source may exist, or the drying approach needs adjustment. Catching these problems early through daily monitoring prevents wasted days and additional damage.

The honest answer is that it depends on the severity of the loss, but most residential water damage jobs require 3 to 5 days of active drying. A straightforward Category 1 loss on hard flooring in a single room might reach dry standard in 2 to 3 days. A multi-room loss with saturated drywall, carpet, and subfloor typically takes 4 to 5 days. Complex losses involving deep saturation of hardwood, plaster, or concrete can require 7 to 10 days or longer.

Several factors affect drying time in Metro Atlanta specifically. Outdoor humidity is the biggest one—during summer months when outdoor humidity regularly exceeds 80%, dehumidifiers work harder because every time a door opens or air infiltrates through the building envelope, it introduces additional moisture. Construction type matters too: older homes with plaster walls hold more moisture and dry more slowly than homes with standard drywall. Pier-and-beam construction with crawl spaces can be challenging because of moisture migrating up from below.

A critical point about shortcuts: removing equipment early because the area “looks dry” or “feels dry” is one of the most common mistakes in water damage restoration. Materials can feel dry to the touch on the surface while still holding significant moisture deeper inside. Only instrument-verified readings determine when drying is complete. We have seen homeowners ask to remove equipment after day two because their floors “seem fine,” only to discover mold growth two weeks later from residual moisture they could not feel.

“Dry standard” is the moisture level that a building material should return to before drying equipment is removed and the job is considered complete. It is not zero moisture—every building material has a natural equilibrium moisture content (EMC) based on the local climate and conditions. Wood in Georgia typically equilibrates around 8% to 12% moisture content. Drywall sits around 0.5% to 1% on a pin meter.

Technicians establish the dry standard for each job by taking readings from unaffected materials in the same structure. If the drywall in an unaffected hallway reads 0.6% on a pin meter, then the wet drywall in the affected room needs to reach that same 0.6% before it is considered dry. This comparison method is far more accurate than relying on generic numbers, because every home has a different baseline depending on age, construction type, HVAC performance, and ambient conditions.

Once all monitored points have reached dry standard for at least one full monitoring cycle (24 hours), the technician documents the final readings, photographs the moisture map, and schedules equipment pickup. This final documentation becomes part of your insurance claim file and serves as verification that the structure was properly dried according to IICRC standards. Without this documentation, there is no objective proof that the drying was completed—which can become a problem if mold or damage surfaces later.