A Reddit user posted a video of a moisture meter maxing out on a plasterboard wall beside their front entrance. The house was built in 2000. There was no visible damage, no swelling and no staining. Yet the meter said the wall was soaking wet.

“What could cause a high moisture reading in a relatively protected entrance like this?” they asked. “What would you investigate to work out the source?”

Andy from Swell Building Inspections answered it for host Jordan in our Pro Insights series. His first answer may surprise you: the meter might be wrong.

Here’s the short answer: a high moisture reading on its own doesn’t prove there’s water in the wall. Some materials, like certain tiles and the steel inside plasterboard walls, can make a meter read 100% when everything is dry. What matters is visible damage, and whether one area reads much higher than the same material nearby.

Moisture Meters Can Give False Readings

“Moisture meters can do funny things,” Andy says. “If you don’t know why they behave certain ways around certain materials, it can be misleading.”

Common causes of false high readings include:

• Certain types of tiles. Some tiles read 100% even when they’re completely dry, because of their density or composition.
• Steel inside the wall. A meter passed over parts of a steel wall frame, or the steel trims used at plasterboard corners and edges, can read 100%.
• Older houses. Some older homes show high readings that have been the same for 60 years without any damage to skirting boards or plaster.

What Inspectors Look for First

A moisture meter is only one tool. Andy says the main thing inspectors look for is visible signs of moisture damage:

• Swelling in skirting boards, door frames or plasterboard
• Moisture staining
• Bubbling or blistering paint
• Around wet areas, signs of recent patching or “makeovers” that might be hiding a problem

If none of those signs are present, a high reading on its own is less likely to mean a real problem, although you can’t be sure without seeing the property.

When a High Reading Is Real: Common Causes

Andy has seen newer homes with genuinely high readings low on certain walls. Usually the cause is outside the house:

Site Drainage Problems

Water pooling against the house because the ground doesn’t drain away from it properly.

Paths Built Too High

Concrete paths or paving poured too high against an external wall, especially against cement sheet cladding, can push moisture into the wall.

Covered Weep Holes

Brick veneer homes have weep holes near the bottom of the brick wall. They let moisture drain out of the wall cavity and let air circulate. If a path or garden bed covers them, moisture gets trapped inside the wall.

Gaps Around Windows and Doors

If the readings are highest near a window or door, look outside for gaps or failed seals that let rain in.

Rising Damp

In masonry walls, salts and moisture drawn up from the ground can cause high readings.

In Tasmania’s cooler, damper climate, moisture problems are among the most common things a building inspection turns up, which makes reading them accurately all the more important.

The Professional Method: Set a Baseline

So how do inspectors tell a real problem from a false reading? Andy describes the approach Swell uses on every inspection:

1. Establish a baseline. Take readings across walls in the same room or area to see what’s normal for that material.
2. Look for differences. A section of wall reading much higher than the rest is worth investigating. For example, a room reading around 20 with one area at 40 to 50.
3. Investigate the source. Check what’s on the other side of the wall, outside, nearby wet areas, windows and drainage.

“You can’t just stick a moisture meter on a certain wall and go, ‘Oh, that’s too high,'” Andy says. If the whole wall reads the same and there’s no damage, it may simply be the material, not water.

It’s a scientific approach: compare against a control rather than trusting a single number.

What This Means for Buyers and Homeowners

• Don’t panic over a single high reading without visible damage. Get it looked at in context.
• Don’t dismiss a reading that’s much higher than the surrounding area, especially near wet areas, windows or ground level.
• Choose an inspector who understands their tools and looks at the whole picture, not just the number on the screen.

Frequently Asked Questions

Why does my moisture meter read 100% when the wall feels dry?

Some materials, including certain tiles and the steel frames and trims inside plasterboard walls, can cause a meter to read 100% even when there’s no moisture.

What causes high moisture readings low on a wall?

Common causes include poor site drainage, paths or garden beds built up against the wall, blocked weep holes, and rising damp in masonry walls.

How do building inspectors use moisture meters?

A good inspector takes baseline readings across similar surfaces to see what’s normal, then investigates any areas that read much higher. They combine meter readings with visual checks for swelling, staining and blistering.

Should I buy a house with high moisture readings?

It depends on the cause. A reading caused by the material itself is harmless. A reading caused by a leaking shower or poor drainage needs fixing. Get an experienced inspector to find out which it is.

The Bottom Line

A moisture meter is a useful tool, but it’s not the whole story. Readings need context: a baseline for the material, a look for visible damage, and a check of what’s happening outside the wall. Swell uses moisture meters and, where relevant, thermal imaging as part of a methodical inspection, looking for the cause rather than just the number.

Andy is a licensed builder with over 15 years of hands-on experience. Every Swell inspection comes with a plain-English report, usually within 24 hours, and a follow-up call to walk you through the findings.

Ready to book? Book your pre-purchase inspection or call 0483 935 688.