Drying Time Calculations for Restoration Pros
How to estimate drying time for a water loss: the four factors that control it, how to size equipment, and the daily readings that prove your number was right.
Every adjuster asks the same question: how many drying days? Bid too few and you eat the extra days. Bid too many and the estimate gets cut. This guide covers how experienced restorers actually calculate drying time, and how to back the number with readings no reviewer can argue with.
The four factors that control drying time
Drying speed comes down to four things, and every one of them is under your control except the last:
- Evaporation load (the water class). IICRC S500 classes a loss from 1 to 4 by how much wet surface area there is and how deeply water penetrated. A Class 1 loss (minimal absorption) can dry in two days; a Class 4 loss (deeply bound water in hardwood, plaster, or concrete) can take a week or more.
- Air movement. Evaporation happens at the surface. Air movers strip the humid boundary layer off wet materials so evaporation keeps running at full rate.
- Dehumidification and temperature. Warm, dry air carries moisture out of materials; the dehumidifier pulls that moisture out of the air. If the air stays humid, evaporation stalls no matter how many air movers are running.
- The materials themselves. Drywall gives up water easily. Hardwood, plaster, and concrete hold it stubbornly. A drying plan that treats oak flooring like carpet pad will blow its deadline.
The baseline numbers
Industry rules of thumb, assuming correctly sized equipment from day one:
| Scenario | Typical drying time |
|---|---|
| Class 1, mostly surface water | 2 to 3 days |
| Class 2, wet carpet and wicking into drywall | 3 days |
| Class 3, saturated from overhead | 4 to 5 days |
| Class 4, bound water in wood or plaster | 5 to 10+ days |
Three days is the norm the industry (and most carriers) anchor on. The number moves when the class, the materials, or the conditions say it should, and your daily readings are what prove it.
Sizing the equipment
Undersized equipment is the most common reason a three-day estimate becomes a six-day job. S500 starting points:
- Air movers: one per wet room at minimum, plus roughly one per 10 to 16 linear feet of wet wall, and one more for every wet inset or offset. Point them at the wet surfaces, angled to sweep the walls.
- Dehumidifiers: sized from chamber volume and class. An LGR (low grain refrigerant) unit is the default for most residential losses. Desiccants earn their place in cold conditions and dense-material jobs, because refrigerant units lose capacity as the space cools.
- Heat: evaporation is physics, and cold materials barely evaporate. In an unheated structure or a winter loss, supplemental heat is part of the equipment list, not a luxury.
Reading the air: temperature, RH, and GPP
Relative humidity alone can mislead you, because warm air holds more water than cool air at the same percentage. Restorers track GPP (grains per pound), the absolute amount of moisture in the air. The daily pattern you want:
- Day 1: GPP in the chamber jumps as equipment drives moisture out of materials and into the air. That spike means the system is working.
- Day 2 onward: GPP falls steadily as the dehumidifier wins. If GPP or RH is still high on day two, something is wrong: a leaking chamber, an undersized or failed dehu, or hidden moisture you have not found yet.
- The finish line: materials read at their dry standard, the moisture content of the same material in an unaffected part of the building.
One monitoring visit per day, minimum: temperature, RH, and moisture content per chamber, written down with the date. That log is what turns "we needed five days" from an argument into a record.
When the calendar and the readings disagree
Trust the readings. If day-three numbers show hardwood still at 18 percent against a dry standard of 9, the job is not done, and a log that shows steady daily progress is what justifies the extra days. If the readings show everything at dry standard on day two, pulling equipment early is a win you can document too.
Where Wave fits
Wave's drying logs (in beta) do this bookkeeping for you. When you build an estimate, Wave drafts a suggested drying plan from the rooms, water category, equipment, and local weather: daily targets for temperature, humidity, and moisture per chamber. You record what your meters actually read, in the grid or by telling Wave in chat, and it flags the day-two stalls and equipment problems described above. Your readings are never changed by Wave, and the whole log exports as a PDF alongside the estimate. See About drying logs, or read how Wave prices the drying work itself.
Related reading
- Water damage categories explained: categories measure contamination; classes measure evaporation load
- Drying log, psychrometrics, and moisture mapping in the glossary
Frequently Asked Questions
How long does it take drywall to dry after water damage?
With proper drying equipment in place, wet drywall typically dries in about three days. Saturated drywall, high humidity, cool temperatures, or water that wicked up from standing flooding can extend that to five days or more. Drywall that stayed saturated with contaminated water usually gets removed rather than dried.
What is a normal drying time for a water loss?
Three days of drying is the industry norm for a typical Class 1 or Class 2 loss with correctly sized equipment. Class 3 losses and dense materials like hardwood or plaster commonly run five to seven days. The honest answer comes from daily moisture readings, not the calendar.
How many air movers and dehumidifiers do I need?
IICRC S500 guidance starts at roughly one air mover per 10 to 16 linear feet of wet wall, plus one per wet room minimum, with dehumidification sized from the chamber's cubic footage and the water class. Bigger chambers, wetter classes, and colder conditions push the counts up.
What moisture level counts as dry?
A material is dry when it returns to its dry standard: the moisture content of the same material in an unaffected area of the structure. For drywall that is typically under about 1 percent moisture content, and for many wood materials a reading within a few points of the unaffected reference.
Why is the humidity in my drying chamber still high on day two?
A stalled day-two reading usually means the chamber is leaking humid air, the dehumidifier is undersized or failing, or there is more trapped water than the initial inspection found. Check containment and equipment first, then re-inspect for hidden moisture.