First, is it really mold growth?
You need to figure out if you’re actually dealing with mold before you start trying to fix the problem. Luckily, you won’t usually need to do any tests. A professional who knows what they’re doing should be able to tell the difference between mold and other things.
Possible false alarms
Looks can be deceiving. Concrete can appear to be white mold growth, especially on wood that has been used for both the concrete foundation and the subfloor. There is an easy way to tell the difference, though. Scratch at it with a screwdriver. If it’s concrete, it won’t budge. If it’s mold, it will easily scrape away, although some staining may remain.
Examples of mold growth
While concrete may not be the easiest material to identify, mold growth in a crawl space is usually easy to recognize. Most of the time, the mold will appear in a round, speckled growth pattern. The more uniform, black appearance is not as common in attics. As the growth intensifies, it expands in a 3-dimensional pattern.
Unusual cases
Fungal growth can occur on a large scale under very specific conditions. These conditions include continuous heavy saturation and luck. The mold you typically find in crawl spaces will not produce this kind of growth. Only a few species of fungi are capable of producing this result. This type of fungal growth can destroy the framing, which traditional molds cannot do.
Is the mold actively growing?
The question of whether the mold growth is from a current problem or a prior issue is important to consider. Mold growth does not fade with time, so it can be difficult to tell how long the issue has been present. For example, mold growth from 20 years ago can look identical to mold growth from 2 months ago.
Use a moisture meter
Moisture in the subfloor or joists/beams above 20% is suspicious and needs to be checked further. The whole crawl space should be checked to see if the moisture is only in one area or if it’s throughout the subfloor. If it’s only in one area, check to see if there are any local plumbing issues.
What if it’s <20%?
If a moisture meter detects more than 20% moisture, it’s likely there is a current issue. However, if the meter detects less than 20% moisture, that doesn’t necessarily mean there is no issue, because mold growth due to condensation can occur at levels that the meter can’t detect. For example, light to moderate growth may occur due to elevated moisture on the surface of the wood. This thin layer of moisture won’t show up with a moisture meter.
Further proof – check behind the insulation
If mold is growing on the subfloor and the subfloor is insulated, it is probably from the home’s original construction. If there is no moisture behind the insulation, then the mold is not from an ongoing problem.
Next, identify the cause of the growth
- Saturation from rain during the original build-out
- Missing vapor barrier
- Poor ventilation (in certain climates)
- Water leak from above
Mold growth from the original construction
In places with wet climates, like the Pacific Northwest, houses that are built during the winter can develop mold problems if they’re not dried out properly. Dryout doesn’t always require dehumidifiers or heaters; often, something as simple as air movers and blowers can do the trick. However, even the most basic dry-out techniques aren’t always used by contractors. This leaves a crawlspace full of saturated lumber sitting on top of saturated soil; essentially, it’s one big experiment gone wrong.
Saturation occurs in two ways:
- Direct contact with rainwater and
- Secondary saturation due to moisture released from adjacent saturated materials, such as ground soil, concrete foundation, etc.
Mold growth due to missing vapor barrier
Primarily an issue in cool climates, the lack of a vapor barrier contributes to the moisture load throughout the entire crawlspace. Additionally, the lack of a vapor barrier can have a significant impact on the moisture load in the conditioned air space above. The physics behind the problem is pretty simple. Diffusion, which is the movement of particles from areas of higher concentration to areas of lower concentration, causes the moisture to migrate upwards in the case of a missing vapor barrier.
Soil microbe growth will not weaken the building, but it can create problems with indoor air quality that are more severe if the ground is damp. A vapor barrier protects against this and is especially important for homes that are likely to have damp ground conditions.
Crawl space flooding
A vapor barrier is not effective when water is sitting on top of it. However, crawlspace flooding typically does not cause mold problems. The exception to this is in hot/humid climates where the additional moisture could cause condensation on the underside of the floor during cooling months.
- Elevated water table
- Improperly installed gutters and downspouts
- Periodic surface flooding
- Rainwater during initial construction
4 signs of mold in your crawl space
A humid crawl space provides the perfect conditions for mold to grow. Mold can easily penetrate wood and cause damage to the structure, as well as health problems.
If you notice any of these four clues, it may be a sign that there is mold growing in your home’s crawl space.
- Strong, musty odors
There is a strong, unpleasant smell of mold coming from the floor and it is getting worse.
- Allergic reactions
Mold growing under homes can often cause allergy symptoms like a runny nose, itchy eyes, headaches, and difficulty breathing.
- Moldy baseboards
If mold is present in the crawl space, it can spread to the baseboards on the floor above.
- Discolored crawl space components
Mold growing on crawl space walls, posts, and floor joists may appear as fuzzy, slimy, or powdery patches.
Look for these color-coded clues.
Black – Most common molds, including Alternaria and Cladosporium
Green mold is also a very common type of mold. It is often caused by Aspergillus, Cladosporium, or Penicillium.
Greenish Black – Slimy in appearance, dangerous Stachybotrys chartarum
White – Variants of Aspergillus, Cladosporium, and Penicillium
Brown – Common Aureobasidium pullulans or Pithomyces chartarum
Yellow – Wood-damaging Serpula lacrymans or Epicoccum nigrum
Orange – Variants of Serpula lacrymans
How to kill mold in crawl spaces: 6 steps to a cleaner home
If you’re hoping to remove mold from your crawl space, it’s crucial that you take steps to protect yourself first. This includes wearing an OSHA-rated respirator or face mask, non-vented goggles, heavy gloves, and disposable coveralls.
- Assess the situation
After putting on your protective gear, evaluate how much mold is in the crawl space. Turn on some lights, and put down plastic sheets so that mold will be caught when it’s cleaned off of surfaces. If the task appears to be too large, contact a mold remediation company immediately.
- Clean with a foaming spray
Spray areas affected by mold with a foaming cleaning product that is specially formulated for mold removal. Allow the cleaner to expand and loosen the mold, and then start cleaning surfaces carefully.
- Soak with a mold killer
Mold that is remaining can be soaked with a mold-killing mixture that can be made at home, or with a mold-removal cleaner. Commercial products are more effective and they often can remove mold stains as well.
- Scrub off residue
Affected areas should be dried and then scrubbed with a stiff brush to remove any mold residue. This process can be time-consuming, but it is important to remove as much residue as possible.
- Dispose of everything
Get a heavy trash bag and carefully fold up your plastic sheeting and seal it in the bag. Do the same with any other gear that may be contaminated such as coveralls and brushes. Store these bagged items outside until trash pickup.
- Control crawl space climate
You can use a dehumidifier to control the climate in your crawl space. Look for a model that is designed to be used in a small space. Check your crawl space regularly during the spring and fall.
How much mold in my crawl space is acceptable?
Mold is something that is found naturally in our environment, but it should not be in your crawl space. Even a small amount of mold can spread quickly, as it feeds on the structural components that are directly under your home.
Airborne mold spores can also enter the house and affect the health of everyone upstairs. There should be no mold present in a crawl space.
Don’t risk your health
As sure as you are of your DIY talents, don’t risk taking on a job that’s too big or too dangerous. We strongly recommend calling in a mold remediation service if:
- Affected areas include damaged or rotted wood.
- Mold covers multiple areas larger than 3 square feet.
- You or any family members deal with allergies or respiratory problems.
A mold remediation specialist can also help identify and eliminate mold sources, as well as repair or replace affected materials.
How much does crawl space mold removal cost?
The cost of removing mold from a crawl space and fixing any damage ranges from $1,500 to $4,000. If the damage is extensive and threatens the home’s structural integrity, the final cost could be even higher.
6 tips to prevent mold in crawl spaces
By following these six tips, you can reduce the chances of mold invading your home’s crawl space.
- Look for leaks
It is important to inspect your crawl space at least twice a year to prevent mold growth. If there is a small leak, it is important to notice it and fix it as soon as possible as this creates an ideal environment for mold. Additionally, if there are plumbing problems upstairs, be sure to check under the house as water always flows down.
A sump pump can help to prevent your crawl space from flooding by pumping out any water that might accumulate.
- Insulate against condensation
One way to protect your pipes from freezing or condensation is by insulating them. This will also prevent mold growth from wet pipe exteriors caused by fluctuating temperatures.
- Fix foundation cracks
If your home has a crawl space, dampness may be seeping in through cracks in the foundation walls. Fixing small cracks now can help to prevent larger mold problems in the future that could spread throughout the home.
- Fight mold with ventilation
If a fungus begins to grow in your home, it will do well in the moist, old environment beneath your home. If you ventilate the space beneath your home, fresh air will move through the area and lower the humidity. This will decrease the number of spores in the air, making it more difficult for mold to spread.
A good tip for ensuring your clothes dryer is effective is to make sure the vent terminates outside of the crawl space.
- Install a vapor barrier
A properly lain vapor barrier also controls humidity, making a crawl space more comfortable and pleasant. A vapor barrier can’t stop all moisture, but it can help prevent mold. The plastic membrane stops natural dampness from rising into the house, which would damage wood, flooring, drywall, insulation, and air quality. A vapor barrier also controls humidity, making a crawl space more comfortable.
- Reroute rainwater
It is important to ensure that your downspouts are properly directing water flow at least 6 feet away from your house in order to lower the risk of crawl space flooding and mold growth under your home. Adding concrete splash blocks can also help to prevent heavy rain from pooling around the foundation.
Crawl space as a storage unit?
It is generally not a good idea to store things in a crawlspace. The only exceptions to this rule are when the crawlspace has a concrete slab and does not have any moisture or mold problems. If you store things in a crawlspace that does have these problems, you will likely find that your stored items will end up smelling musty, and covered in mold or rodent droppings.
Mold growth due to water leaks from above
The water from a pipe leak or failing toilet seal will go into the crawlspace if it occurs on the first floor of a home. Most people don’t want to go into the crawlspace, so the moisture buildup often goes undetected. The most common culprit for this is bathroom issues. If there is a catastrophic incident such as a burst pipe, it will wreak such havoc that the entire home will be investigated. A leak from a toilet seal or shower pan is typically slow and can go undetected for months. Once the first sign of an issue is observed, extensive damage has often already occurred.
Mold in crawl spaces: The health issues
Tackling mold in crawl spaces is dangerous because they are dark, humid, and badly ventilated. This makes them ideal for a mold outbreak which can pose serious health hazards in such a compact space.
The type of mold growing in your home can have an impact on your health. White mold is easier to get rid of than Stachybotrys chartarum, which is a type of black mold that can be very harmful if inhaled. If you have this type of mold in your home, it’s best to call a professional to remove it, as attempting to do it yourself can be dangerous.
You should test the mold before you start to clean it up. This way, you will know exactly what you are dealing with.