Mold in the Attic or Crawl Space: Causes, What to Check, and Who to Hire

Why Moisture Causes Mold

Mold spores are always in the air, both inside and outside your home. Mold cannot grow without moisture. If you find mold, you must clean it up and fix the water problem that caused it. If you clean the mold but do not fix the water problem, the mold will likely come back, as the U.S. Environmental Protection Agency (EPA) explains. The EPA says that the key to mold control is moisture control. It is impossible to get rid of all mold and mold spores indoors, but mold will not grow without water or moisture.

In crawl spaces, mold often grows in hidden areas, especially if the ground is bare earth. The EPA’s mold course explains that the soil pulls up moisture. The warmth in the crawl space then dries this soil by evaporation, sending moisture into the air. This moist air can cause mold to grow. If the water table is high, groundwater can also enter a crawl space. Moisture from a crawl space can even move into other parts of your home through cracks in walls, floors, and ceilings, leading to more mold growth. The EPA says crawl spaces should be designed to avoid moisture problems.

In attics, moisture problems often come from several sources. ENERGY STAR lists signs of trouble including wet or damp insulation, which can mean your roof is leaking. Moldy or rotting wooden parts, like rafters or floor joists, also point to water damage. Kitchen, bathroom, or clothes dryer vents that send moist air into the attic instead of outside can also create a damp environment. Little or no attic ventilation can also trap moisture, leading to mold. ENERGY STAR says to fix these issues before sealing your attic.

What to Check in Your Attic

When you check your attic, look for certain signs of moisture and mold. ENERGY STAR suggests looking for:

• Dirty or darkened insulation: This shows that house air is moving through the insulation. The darkening comes from the insulation filtering dusty air.
• Frosty areas: In cold weather, warm, moist air from your home can condense and freeze in the attic. You might see frosty areas in the insulation.
• Water staining: In warmer weather, the same areas where you might see frost in winter could have water stains.

Safety Tips for Your Attic:

• Walk on joists or truss chords: These are the strong wooden beams that support the floor or ceiling. Do not walk on exposed ceiling drywall or insulation, as you could fall through.
• Watch for nails: Be careful of nails pointing up through the ceiling or down from the roof.
• Vermiculite insulation: Some attics have vermiculite insulation. This type of insulation may contain asbestos. Do not disturb it unless it has been tested by an approved lab. Asbestos can be dangerous if disturbed.

What to Check in Your Crawl Space

Crawl spaces are common places for hidden mold growth. The EPA explains that a bare earth floor can wick moisture from the ground. This moisture then evaporates into the air, making the crawl space very humid. This high humidity creates perfect conditions for mold to grow. If the water table is high, groundwater can also enter the crawl space, adding to the moisture problem. This moisture can travel through cracks into the rest of your home, causing mold to grow in other areas too. The EPA says crawl spaces should be designed specifically to avoid moisture problems.

How to Control Moisture to Prevent Mold

Controlling moisture is the best way to prevent mold. The EPA offers these tips:

• Clean gutters: Regularly clean and repair your roof gutters.
• Ground slope: Make sure the ground around your home slopes away from the foundation. This prevents water from collecting near or entering your home.
• Vent appliances outside: Vent moisture-producing appliances, like clothes dryers, to the outside of your home. This reduces humidity indoors.
• Use bathroom fans: Run your bathroom fan or open a window when showering to remove moist air.
• Insulate cold pipes: Cover cold surfaces, such as cold water pipes, with insulation. This helps prevent condensation from forming.

If you see condensation or moisture on windows, walls, or pipes, dry the wet surface quickly and find the source of the moisture to stop it.

When to Hire a Professional for Mold

Sometimes, mold problems are too big or too complex to handle yourself. The EPA suggests getting professional help when the moldy area is more than about 10 square feet (roughly a 3 foot by 3 foot patch), when there is extensive water damage, when sewage or contaminated water is involved, or when the heating and cooling system may be contaminated.

If mold is suspected of damaging the structure of your home, the EPA says you should consult a structural engineer or another professional with relevant expertise. Molds can gradually destroy what they grow on. If a mold and moisture problem goes on for too long, it can weaken floors and walls by feeding on wet wood.

ENERGY STAR also recommends hiring a professional to fix certain attic problems before doing any air sealing. These include:

• Difficult access or limited space to work in the attic.
• Wet or damp insulation, which means your roof is leaking.
• Moldy or rotted rafters or floor joists.
• Kitchen, bathroom, or clothes dryer vents that send moist air into the attic instead of outdoors.
• Little or no attic ventilation.
• Old knob and tube wiring, which can be a fire hazard if it touches insulation.

If you have an appliance that uses oil or gas, ENERGY STAR also suggests hiring a home performance contractor. They can test that the appliance properly vents combustion gases before and after air sealing, as sealing can sometimes cause these appliances to send gases back into your home.

How to Choose a Mold Cleanup Contractor

If you decide to hire a contractor (or other professional service provider) to clean up mold, the EPA advises you to take these steps:

• Experience: Make sure the contractor has experience cleaning up mold.
• References: Ask for and check their references.
• Guidelines: Ask the contractor to follow recommended guidelines, such as those from the EPA’s “Mold Remediation in Schools and Commercial Buildings” or other professional or government organizations.

If the water or mold damage was caused by sewage or other contaminated water, the EPA says to hire a professional who has experience cleaning and fixing buildings damaged by contaminated water.

When this advice may not fit

This advice helps with typical mold and moisture issues. However, you should get help from a qualified professional if you suspect structural damage from mold, have a very large mold problem, or if the mold is from sewage or other contaminated water. For your safety, you must hire a qualified professional for any work involving gas lines, the electrical panel, your roof, or structural parts of your home. A qualified professional should also handle asbestos or lead removal.