How Mold Growth Really Happens (It’s Not Just Obvious Leaks)

When most people think about mold, they picture a major plumbing leak or a flooded basement. While those situations can certainly lead to mold growth, they are not the most common causes we see during inspections.

In reality, mold often develops quietly—without dramatic water events. Understanding how mold growth actually occurs can help homeowners spot problems earlier and prevent unnecessary stress.

At Utah Mold Pros (UMP), education comes first. Below are the most common ways mold growth occurs in homes—many of which go unnoticed.

1. Chronic Humidity

Mold doesn’t require standing water. Elevated humidity alone can be enough to support growth over time.

In Utah homes, this often shows up in:

• Bathrooms without proper ventilation

• Laundry rooms

• Basements and crawlspaces

• Homes with oversized or improperly balanced HVAC systems

When indoor humidity consistently stays above ~60%, building materials can slowly absorb moisture—creating ideal conditions for mold.

Key takeaway: Even without leaks, high humidity can quietly fuel mold growth.

2. Condensation on Cold Surfaces

Condensation is one of the most overlooked contributors to mold.

It commonly forms on:

• Windows and window frames

• Exterior walls

• HVAC ductwork

• Pipes running through unconditioned spaces

When warm, moist indoor air meets a colder surface, moisture forms—even if only briefly. Repeated condensation cycles can dampen materials long enough for mold to establish.

Key takeaway: You don’t need visible water damage—repeated condensation is enough.

3. Poor Ventilation

Modern homes are built to be energy efficient, but tighter building envelopes can trap moisture indoors.

Common ventilation-related issues include:

• Bathroom fans that are undersized, broken, or not vented outdoors

• Kitchens without functional exhaust systems

• Bedrooms or basements with limited air movement

Without proper airflow, moisture lingers longer than it should.

Key takeaway: Moisture that can’t escape will eventually find a place to settle.

4. Small, Ongoing Leaks

Not all leaks announce themselves.

Slow leaks behind walls, under sinks, or around appliances may never create visible damage—yet they can keep materials damp for months or years.

Common sources include:

• Supply line fittings

• Refrigerator ice makers

• Toilets and shower valves

• Exterior penetrations

Key takeaway: The most problematic leaks are often the ones you don’t see.

5. Building Design & Materials

Certain materials and construction details are more prone to moisture retention.

Examples include:

• Drywall and paper-backed insulation

• Poor drainage or grading around foundations

• Inadequate flashing around windows and roofs

Mold growth often reflects how a building manages moisture—not just occupant behavior.

Key takeaway: Mold is often a building science issue, not a cleanliness issue.

Mold Is a Symptom, Not the Root Problem

Mold growth is a signal that moisture is not being properly controlled. Focusing only on surface cleaning or testing without understanding why moisture is present often leads to recurring issues.

At Utah Mold Pros, we focus on:

• Identifying moisture sources

• Understanding airflow and humidity dynamics

• Providing clear, practical guidance

Our goal is to help homeowners turn uncertainty into understanding—without fear or pressure.

If you have questions about moisture, mold, or indoor air quality in your home, we’re always happy to help.

Utah Mold Pros
ACAC-Certified Mold Inspectors
Serving homeowners across Utah