What Causes Mold Growth

Date Published: March 19, 2019

While mold spores are everywhere in the air, it can become more problematic when higher concentrations are present in your home. It can cause a person to become ill if they are exposed to it long enough, including respiratory and breathing concerns.  It is important for you to know what causes mold growth and where it is commonly found in a home.

Once you know what to look for and how to address concerns, mold doesn’t have to be that scary monster that it is made out to be.  In the event you do find any mold growth, you’ll know exactly how to mitigate it from your home. If it is severe enough, there are professionals who know how to test for mold and perform proper clean up and mitigation.

What causes mold to grow?

The key word here is moisture. First off, if a part of your house is moist due to a consistent water leak (for example, a dripping but slowly leaking pipe inside a wall or ceiling), that will be ground zero for mold growth.

Want to take an air sample in your home today? Our air sample mold testing will give you a clear picture of air born mold spors that may be contaminating the air you breathe. Learn more here.

The four components needed for mold to grow in your home are:

1) mold spores which are everywhere in the air we breath

2) oxygen (thankfully also everywhere)

3) a food source such as wood, drywall paper backing and

4) water/moisture

If you remove the water and moisture component, then the mold spores in the air have no means to gather and grow.  So dealing with moisture is the number one way to prevent or stop mold growth.

mold growth on drywall

Common areas of concern

If you suspect that mold growth is present and may be the cause of your health concerns, or if you just smell damp musty conditions and suspect mold, the first thing to do is to search out moisture or water concerns.  Common concerns that cause mold growth are;

  • Water leaks – even the smallest of drips from a supply or drain pipe can cause moisture to gather and pool or to saturate building components.  Look for signs of moisture pooling, increased water bills, stains on drywall ceilings, or other common indications of a leak present.
  • Bathroom tub-tile sealing – that deteriorated caulking or sealing around the base of the tub or the edge of the shower can cause moisture to wick up into areas, wetting construction material behind the area, causing mold to gather and grow.
  • Roof leaks – flashing issues and aging roofing material can cause leaks to develop.  As moisture wicks down into the home, it can move into areas causing mold growth behind walls and in attic spaces.
  • Poor grading and drainage – failure to keep your gutters clean, downspouts not extended away from the home, and landscaping that isn’t sloped properly from the home can all be a cause of moisture gathering around the foundation and having a chance to get into the home through minor cracks and gaps.

One of the best resources for a general understanding of mold in the home is the EPA guide to mold, moisture and your home.

Testing for Mold

If you do find the source of the water leak, the first and best thing to do is to address the leak first, which is the root cause of the mold growth.  Once you have the leak addressed, then you can address the mold growth and properly mitigate.  And if you can physically see mold present, the need to test the mold is debatable.

At that point, mitigation is needed to remove the mold growth that is present, clean up the area, and restore the area to proper condition.  However, if you can’t find the source of the mold, or if you aren’t even sure that mold is present, then mold air-sample-testing is the recommended course of action.

Testing can be done in different areas of your home, to help understand if elevated levels of mold spores are present, and to help identify where the mold may be in higher concentrations.  The results of that testing can help to know where to focus your efforts to pinpoint the cause of the mold growth.

Mitigating Mold Areas of Concern

It is generally recommended that small mold clean up efforts can be done by the homeowner.  If the area is less than 10 square feet, the EPA advises that this can be cleaned up following simple tips and techniques.

Larger areas should be left to a mitigation specialist.  There are many mold remediation contractors who can come into a home, remove any affected building materials such as drywall, then clean and treat other items and areas, preparing them for refinishing.

If you do suspect that mold growth and airborne mold levels have contaminated the heating and cooling ducts, then duct cleaning can be performed.


The important thing to remember is that water is the key to what causes mold growth in your home.  If you notice any potential leaks or moisture inside your home, investigate it further to fix and repair the cause.

If you have caught it in the early stages of growth, you can get rid of it safely and properly using the right cleaning methods. If it becomes an even bigger problem where it can harm the structure of your home, find a mold mitigation expert near you.

At Scott Home Inspection, we can perform mold inspections and testing to help clients locate the cause of moisture concerns and understand the extent of moisture damage or mold growth.

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About the Author: George Scott

George founded Scott Home Inspection in 2006, and has grown the business into a multi-inspector firm serving the Colorado Front Range, from Fort Collins down to Colorado Springs. As an ASHI Certified Home Inspector and Certified Energy Rater, George is an excellent resource to help with inspection and energy-related requirements.

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