Ceiling Moisture Detection Guide

Goal

What to use (ranked)

1. Moisture meter — Pin‑type for precise spot readings. Pinless for fast, non‑destructive scans.

2. Hygrometer — Checks room humidity to spot broader moisture problems.

3. Optional: Thermal camera — Helps find cool spots that may indicate moisture, but confirms nothing on its own.

5‑step quick check

1. Scan visually
• Look for stains or rings
• Bubbling or peeling paint
• Sagging drywall
• Any visible mold spots

2. Measure humidity (hygrometer)
• 30–50% RH is typical indoors
• Persistent 60%+ suggests a moisture source

3. Map suspect areas (pinless meter)
• Sweep the ceiling in a grid
• Mark any areas that read clearly higher than surroundings

4. Confirm with pins
• Use a pin meter on the marked spots and a nearby “dry” control area
• Record readings for each spot

5. Plastic sheet test (if unsure)
• Tape a 12×12 in plastic sheet airtight to the ceiling over a suspect spot
• Wait 24–48 hours
• Condensation under plastic = moisture problem

Reading targets

• Dry drywall: often under ~12% MC

• Elevated: ~12–17% MC (monitor and investigate)

• Wet/urgent: 17%+ MC (find source and remediate)

Source checklist

• Above a bathroom or kitchen?

• Recent rain or snowmelt?

• Plumbing lines or fixtures above?

• Roof penetrations nearby (vents, chimneys, skylights)?

• HVAC or condensation lines overhead?

If you have a thermal camera

• Use after 10–15 minutes of HVAC running to increase temperature contrast

• Look for cool anomalies in patterns that match gravity paths or framing

• Always confirm anomalies with a moisture meter before cutting

Minimum viable reset (10–15 min)

• Ventilate: open a window or run exhaust

• Dehumidify: run a dehumidifier to ~45% RH

• Mark and log: circle suspect areas with painter’s tape and note meter readings and RH

• Recheck in 24 hours

Safety and damage control

• If ceiling is sagging or soft: place a bucket, protect the floor, and avoid standing under it

• If staining grows after rain: tarp or contain, then inspect roof the next dry day

• If moldy smell or visible growth: wear PPE (N95, gloves), limit disturbance, increase ventilation

When to call a pro (Monica‑level standards)

• Repeated readings 17%+ MC after 48 hours of drying efforts

• Active drip, visible mold >10 sq ft, or electrical nearby

• Unknown source above finished ceiling

Log template

• Date and time

• Room RH: __ %

• Pinless hotspots: locations + relative values

• Pin readings: location — __ % MC

• Weather/usage notes: rain, shower use, HVAC state

• Action taken and next check time

Decision flow

1. No anomalies and RH <55% → Monitor weekly for a month

2. Elevated RH or minor hotspots (12–17% MC) → Dry, ventilate, recheck in 24–48 hours

3. 17%+ MC or spreading stains → Find source now, open a small inspection hole if safe, or call a pro

Tools and budget

• Pin moisture meter: $30–$50 basic is fine for drywall

• Pinless moisture meter: helpful for mapping, $50–$150

• Hygrometer: $10–$20

• Optional thermal camera: rental or smartphone add‑on if needed

Pro tip