mold in crawl space

Mold in Crawl Space: The Causes & Solutions Homeowners Need To Know About

Kenneth Wilson

The crawl space of a house is probably one of the most overlooked areas. Most people even forget the area exists. However, this makes it the perfect home for mold to grow. If you are facing a moldy situation in your crawl space, don’t worry. I will share everything that you should know on do to deal with mold in crawl space.

Most mold issues found in crawl spaces is caused by high humidity and moisture. Depending on the type of mold, they can be extremely toxic and may pose some serious health hazard. You can choose to remove the mold by yourself, but the process can be quite taxing for most homeowners, especially if the case is severe. So, we recommend to hire a professional as it is the most convenient and safest way to go.

In addition, dealing with mold issues in your crawl space can be complex and you need proper knowledge to rid of it for good. To guide you further, I will discuss what causes mold in your crawl space, the dangers it poses and ultimately, how you can deal with it professionally or by yourself.

Dangers of Crawl Space Mold

It’s no surprise that living with mold in your crawl space is not ideal. There are many dangers to having a mold infestation in your home. To make it worse, the risks that mold may expose you to is more hazardous than you think. Let's look at some of these consequences so you can understand the severity of the issue.

Terrible Musty Smell

Most molds are invisible to your naked eye. But even if you are not able to detect them with your sense of sight, you may be able to do it with your sense of smell. Most mold species give off a strong unpleasant and musty smell and it’s not an enjoyable experience at all. 

It’s especially terrible when mold spores are growing in your crawl space because the source of the smell can be hard to identify. So I would recommend not ignore that musty smell you've been noticing for weeks and have your crawl space inspected.

Causes Allergies

Not everyone out there is allergic to mold. But when you are, the growth of mold in any area of your house can be the most horrible experience you can imagine. The symptoms you face from mold allergy are quite similar to the symptoms experienced with infections of the upper respiratory area.

The severity of the symptoms will range from mild to serious depending on the person. Usually, the symptoms seem worse when you are in an area where the mold concentrations are high. These are the following symptoms to look out for:

  • Excessive sneezing or coughing
  • A stuffy and runny nose. There might also be a postnasal drip
  • Itchy and teary eyes
  • Skin irritation or rashes
  • A sore throat
  • Sinus irritation

Toxic Mold Syndrome

Another serious side-effect you might face from mold growing in your home is toxic mold syndrome. This is not a common side-effect but when it happens it's very serious one. When you suffer from the symptoms of this problem, you must consult with a physician immediately. The symptoms may include:

  • Memory loss or mental confusion
  • Difficulties with concentration
  • A lack of sleep or insomnia
  • Anxiety or depression
  • A lack of appetite

HVAC Issues

When there is mold in your crawl space, chances are, it has already spread in all the other areas of your home. If it manages to get into the HVAC system of your house, it can easily travel to the rest of your home through the air ducts. 

If mold has reached into your HVAC system, it can be really difficult to get rid of. When this is the case, your best bet is to hire a professional to remedy the problem.

Harms Your Home and Lessens Its Value

ceiling collapsing due to mold

Mold spores feed on any organic material it finds and can cause a lot of harm to your home. Any organic materials such as wood, glue, paper, or fabrics are a source of food to mold and will deteriorate severely. With time, the drywall might rot, carpets, wallpaper, and many other parts may be damaged as well.

There might be cases when the mold damages are so extreme that your ceilings may collapse, the wall may fall or the floors may cave in. So, it’s extremely important to address any moldy situation in your crawl space. It can cause irreparable damage to your house. 

Having mold in your crawl space makes it extremely difficult to sell your house. Due the dangers of mold being covered in the news, homeowners and potential buyers are more careful about it than ever. If any potential buyer finds mold in the home you’re trying to sell, you will probably face a big decrease in the sale and need to settle for a lower price. 

Causes of Mold in Crawl Space

Technically speaking, there is no place where you won’t find mold spores no matter how clean it is. When these mold spores are exposed to a relative humidity of about 60% or more and a temperature of 40 degrees or higher, it’s an ideal condition for mold growth. For mold spores to grow on wood, it needs to have at least 20-29% moisture content or more.

Crawl spaces are quite warm because of the home it holds above and the natural warmth from the ground beneath. So, how moisture gets into your crawl space is the main cause behind mold growth. The following reasons are the most possible causes behind any moisture in your crawl space:

Penetrating Damp in the Crawl Space

One of the most common causes of moisture in your crawl space is “Penetrating damp”. This usually occurs in older buildings. This tends to happen more in enclosed crawl spaces. 

Penetrating damp means when moisture makes its way into your crawl space through an external source. These sources include plumbing leaks, walls, your HVAC, or other mechanical failures above the crawl space or within.

Rising Damp

Rising damp is a rare form of damp that refers to any moisture that travels from the ground to an upwards area. This is one of the major causes of moisture in your crawl space.

Rising damp occurs when crawl spaces don’t go through encapsulation and aren’t protected with a vapor barrier. This causes continuous dampness in the crawl space and helps wood-decaying fungus and molds to grow. 


In some houses, crawl spaces are ventilated from time to time. This is done by using outside air as a source to control any moisture. Any excess moisture in the space would get evaporated using this method to prevent any mold growth. But in many cases, the ventilation causes the opposite and encourages the mold growth. 

This happens because the outside air is warmer and when it comes into contact with the cold air of the crawl space, the warm air cools down and releases moisture in the space. Due to the condensation, there is enough moisture and organic materials in the crawl space such as wood, paper, and other things that becomes food for mold spores to grow.

Types of Molds That Grow in Crawl Spaces

Molds can spread quickly and early detection can be crucial if you want to prevent an outbreak. The best way you can identify mold is with the smell. If you smell any musty smell from your crawl space, it’s the tell-tale sign of mold growth. Visual signs include white powdery substances on beams or floor joists. 

The most common types of molds that grow in house gold crawl spaces are white molds, yellow molds and black molds. But there are many other types of molds and it’s important to know about them to prevent any outbreak from happening. The following are the most common types of crawl space mold:

White Mold 

White mold is a harmful type of mold that you can find growing in the ground or floor joists of your crawl space. It can release harmful toxins in the area and is very hazardous to your health. This type of mold often grows up in warmer weather and is uncommon when it is cold. 

Yellow Mold 

Commonly known as “House-eating mold”, yellow mold in the crawl space commonly grows and feeds on wooden structures. So, any wooden structures with this mold will slowly decay and deteriorate with time. Before it eats up your house and causes it to collapse, you should get rid of it. 

Black Mold 

These are the most dangerous type of toxic mold and you do not want to find this growing in your crawl space. There are two variants of this mold and both are equally hazardous to your health. This mold will produce harmful mycotoxins that can trigger allergies or worsen any existing respiratory problems such as asthma. 

To the naked eye, they seem mostly dark gray or green. They mostly appear flat instead of fluffy, powdery, fuzzy, or bumpy. This type of mold can grow in the dirt, on your drywall, subflooring, carpet, or even insulation. 

If you find this type of mold in your crawl space, never try to deal with it by yourself. The best solution is to hire a professional so you don’t end up inadvertently spreading this mold to any other area of your home.

How to Remove Mold from Crawl Space?

As discussed, mold poses a number of serious risks to your home and your health. Thus, if you find any mold growing in your crawl space, you need to take action as soon as you can.

If you plan to remove the mold by yourself, make sure to take the necessary measures to protect yourself from the hazards of cleaning the mold. In addition, you need to know exactly what to do as removing the mold from your crawl space is a complex process. Let’s look at all the steps you need to follow to remove mold from your crawl space safely and efficiently:

Step 1

Put On Your Safety Gear

First, make sure you are protected from potential health risks.  You can use gloves made with textured-grip materials on the fingertips and palm. They are made to handle slippery tools with ease. 

When you are using strong chemical commercial cleaners or other homemade ones with bleach or ammonia as the base, make sure to cover your eyes and mouth. Moreover, wear a chemical or dust mask to avoid inhalation of toxic mold and chemicals. 

Step 2

Carefully Assess the Situation in Your Crawl Space

In this step, you will need to set up lights in the crawl space and place plastic sheets on the ground. You can use the sheets to catch any mold when you clean them. 

Step 3

Use a Foaming Spray to Clean 

You can purchase foaming sprays specifically designed to remove mold. Use it to spray affected areas and then give it some time to expand and loosen all the mold. 

Step 4

Use a Mold Killer

Soak any remaining mold with mold-removal cleaners or homemade mold-killing mixtures. You can find DIY solutions but it’s best to use commercial products as they are more effective and are made to remove mold stains as well.

Step 5

Get Scrubbing

When the affected areas dry off, use a bristle brush to scrub all the remaining mold away. This can make the whole process very lengthy but is a necessary step. You want to make sure that all the mold residue is properly removed. 

Step 6

Dispose of the Mold

Carefully pick up your plastic sheets and seal them away in a trash bag. Any brush, gear, or equipment you used is probably contaminated and should be disposed of as well. 

Step 7

Control the Climate of Your Crawl Space

Once, the cleaning process is done with, remember to control the climate down there to prevent any further mold regrowth. A dehumidifier is a very effective and affordable option that can help with controlling the climate in the crawl space.

DIY or Hire a Professional? 

In mild mold cases you can take the job in your own hands. But, in extreme crawl space mold situations, you should hire a professional. As previously discussed, mold growth in the crawl space can be dangerous for your health and home. Thus it is best to deal with it immediately.

Molding is considered extreme when the surface area on which there is mold is equal to or more than 3 x 3 ft. 

Before you take any step to remove all the toxic mold growth in your crawl space by yourself, there are a few things you need to consider: 

First, consider the physical and health condition of yourself, anyone in your family, and your neighbors. If there is no one with a history of asthma or other respiratory problems or any children, you can do it yourself. 

Next, you need to consider the severity of mold growth. If the mold growth seems small, you can consider choosing to DIY. As long as you have sufficient knowledge and all the equipment for safe and thorough removal of mold growth, you should face no problem. 

There are soap and cleaners commercially available that can kill and remove molds. If you are a handy person, replacing affected drywall or insulation should also be easy. 

WHEN TO hire Professionals

  • Extreme mold problem
  • If someone in your household has any respiratory problem
  • If mold is airborne
  • If you are inexperienced with treating mold problems

when it is safe to


  • Mild mold problem
  • If no one in your household has a respiratory problem (asthma etc.)
  • You have sufficient knowledge in mold remediation
  • You have the right equipment to treat the problem

But if you consider the job to be very big, complicated, and dangerous, hire a professional. Having anyone in your vicinity with asthma or other respiratory problems is another reason to hire professionals for the job. 

You must hire a professional when the mold is airborne and has already spread into many structural elements in your house. If the amount of mold visible on the surface seems more than 3 by 3 feet, it’s absolute that you bring in professionals to deal with it. 

A professional mold removal expert knows the proper procedure to remove all mold from your crawl space. They have different solutions depending on the type of molds, how long they have been growing and the affected area of your house.

Final Thoughts

Crawl spaces are one of the most common and convenient places for mold growth. Facing this issue can be extremely frustrating and dangerous, so you need to act on it now to avoid further risks.

If you have a molding problem, I hope this article was able to help you. Thank you for reading up to this point and best of luck with your mold situation.

Kenneth Wilson
July 30, 2021

Kenneth Wilson

Retired contractor. Currently residing in Southwest Florida. Now in semi-retirement, I write and manage this blog focused on helping home owners make savvy decisions when it comes to finding contractors and getting their projects done. I also operate remodeling design service for homeowners.

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