How To Get Rid of Attic Mold

Mold is a health hazard that needs to be remedied quickly. Attic mold forms when warm, moist air from your living spaces meets the cold underside of your roof, creating condensation. This moisture, combined with organic materials such as wood, creates the perfect breeding ground for mold. In the video above, This Old House general contractor Tom Silva demonstrates a professional approach to eliminating dangerous attic mold outbreaks.

Signs of Attic Mold

If left unchecked, mold can lead to respiratory problems, allergic reactions, and even structural damage to your home. Before it can be removed, you have to figure out how widespread the problem is, why it’s happening, and how to avoid it going forward.

Identifying mold in your attic is the first step in figuring out the right treatment. Here are some common indicators:

• Musty odors
• Discoloration on wood surfaces
• Visible mold growth on insulation
• Damp or wet spots on the attic floor or walls

Causes of Attic Mold

Several factors contribute to mold growth in attics, such as the following:

• Poor ventilation
• Roof leaks
• Inadequate insulation
• High indoor humidity levels
• Improperly vented bathroom or kitchen exhaust fans
• Critter infestations that leave behind urine

Understanding these causes can help you prevent future mold growth after cleaning up the existing problem.

In many cases, the process starts in winter: warm, moisture-laden air from the heated rooms below leaks up through the attic floor and hits the cold underside of the roof sheathing. The moisture condenses—and can even form frost on the plywood and nail tips. As temperatures warm up and the icy sheathing thaws out, conditions become perfect for mold to colonize the wet wood. As the sheathing eventually dries in summer, the mold goes dormant—but it will start growing again the next time conditions are right.

Professional Mold Removal Techniques

While minor mold issues can sometimes be addressed by homeowners, extensive mold growth requires professional intervention. The method Silva demonstrates in the video involves using specialized equipment and techniques to guarantee thorough mold removal.

Another professional approach demonstrated on This Old House is a multi-step process that begins with soda blasting—using bicarbonates (essentially baking soda) to remove about a sixteenth of an inch of material, eliminating the mold and any residual spores from the surface. Next, an air scrubber pulls any airborne spores larger than 0.3 microns out of the air. The crew then HEPA-vacs the area to capture any remaining spores, applies a biocide via a foam process, and finishes by fogging the space to neutralize any lingering spores still in the air.

Dry-Ice Blasting

One effective method for removing attic mold is dry-ice blasting. This technique uses compressed air to propel dry-ice pellets at high speeds, effectively removing mold without damaging the underlying wood. It leaves no residual moisture that could promote further mold growth.

The process works by loading dry-ice pellets into a hopper, which feeds them up a blast hose and out through a nozzle at roughly 1,000 miles an hour — similar to a sandblaster. The pellets, which are solid carbon dioxide at about 110 degrees below zero, sublimate on contact, going directly from a solid into a gas. The combination of kinetic impact and extreme thermal shock profiles the surface just enough to blow mold right off the sheathing and down to bare wood.

Containment and Air Filtration

To prevent mold spores from spreading through your home during the cleaning process, professionals use containment and air filtration techniques. This includes covering the attic floor with polyethylene sheets, setting up negative air machines for filtering, and using HEPA vacuums to collect mold dust and debris.

DIY Mold Prevention and Maintenance

While professional cleaning is often necessary for extensive mold problems, there are steps homeowners can take to prevent mold growth and promote a healthy attic environment.

Improving Attic Ventilation

Proper ventilation plays a big part in mold prevention. Here are some ways to improve your attic’s ventilation:

• Install ridge vents and soffit vents.
• Ensure existing vents are not blocked by insulation.
• Add attic fans for increased air circulation.

Don’t Forget Exhaust Ducts: Make sure bathroom fans, kitchen exhaust fans, and dryer vents are routed directly to the outside—never into the attic. As Tom Silva warns, “The fans have to be vented outside the house, not into the attic. Otherwise you’re dumping moisture on the underside of the roof.” In his own home, he installed timer switches to allow bathroom fans to run for a full hour after use. Also seal any gaps that allow indoor air to enter the attic, and reroute any ducts that exhaust into that space. If you don’t take these precautions, even a perfectly ventilated attic can develop mold.

Addressing Moisture Sources

Eliminating sources of moisture is key to preventing mold. Take these steps to reduce moisture in your attic:

• Repair any roof leaks promptly.
• Ensure bathroom and kitchen exhaust fans vent directly outside.
• Use a dehumidifier in damp climates.
• Check and maintain gutters and downspouts to prevent water from seeping into the attic.

Prioritize Attic Ventilation: Soffit and ridge vents are more effective ventilators than powered fans, and they don’t use any energy. A ridge vent paired with continuous soffit vents circulates cold air under the entire roof. Both ridge and soffit vents should have the same size openings, and provide at least 1 square foot of opening for every 300 square feet of attic floor. Place baffles at the eaves to maintain a clear airflow path from the soffits, and make sure existing vents aren’t being blocked by insulation.

Regular Inspections

Regularly inspecting your attic can help you catch mold problems early. During these inspections, we recommend you do the following:

• Look for signs of water damage or discoloration.
• Check insulation for dampness.
• Inspect the underside of the roof sheathing for condensation or frost during winter months.
• Monitor humidity levels with a hygrometer.

Detailed Steps To Clean Attic Mold

Knowing how mold develops and recognizing the signs are important, but tackling the mold head-on requires a structured approach. Here’s how to handle it.

Preparation

Before starting the mold removal process, gather the necessary tools and cleaning agents where you’ll do the cleaning. You don’t want to track anything back and forth throughout your home. Wear protective gear, including a mask and gloves, and keep the attic well-ventilated throughout the process. Keep away children, pets, and anyone with respiratory issues.

Gear Up Right: Beyond a basic dust mask, use a high-efficiency particulate air-purifying (HEPA) respirator — look for one equipped with a chlorine cartridge if you’ll be using a bleach solution. Wear goggles, rubber gloves, and disposable plastic suits to protect your clothing and skin from mold spores. Workers on TOH projects wear full disposable suits specifically so contaminated clothing doesn’t leave the work area.

Cleaning Process

Remove all stored items from the attic, placing anything you think may be contaminated outside. For sentimental or expensive items, use a mold-specific cleaner and leave them outside to dry completely before bringing them back in. Clean them twice to be cautious. Vacuum the attic to remove loose mold spores and debris. Clean affected surfaces with a mold-removing cleaner or a mixture of white vinegar and water.

Drying and Prevention

After cleaning, thoroughly dry the area. Use fans and dehumidifiers to reduce moisture levels. Apply a mold-inhibiting spray to prevent future growth, and seal any cracks or gaps to prevent moisture entry.

Advanced Attic Mold Remediation Techniques

Advanced remediation is sometimes necessary for more severe mold infestations. Here are some intensive techniques used by professionals for comprehensive mold removal and long-term prevention.

Fogging

Fogging is an advanced technique where a mold-inhibiting solution is turned into a fine mist and sprayed throughout the attic, reaching every nook and cranny. This method helps eradicate mold spores from hidden areas and prevents recurrence.

Soda Blasting

An alternative to dry-ice blasting, soda blasting uses sodium bicarbonate particles propelled at high speeds. This method removes mold effectively and is less abrasive on surfaces. It’s ideal for delicate areas where dry-ice blasting might be too harsh.

UV Light Treatment

UV light can break down the DNA of mold spores, rendering them inactive. It’s a chemical-free option that can be used in conjunction with other methods for a comprehensive cleanup.

Attic Environmental Controls

Keeping mold at bay requires a balanced environment within the attic. Implementing environmental controls can significantly reduce mold formation risks, ensuring long-term peace of mind.

Improving Insulation

Better insulation helps regulate your home’s temperature, reducing condensation that can lead to mold growth. Using high-quality, mold-resistant insulation materials can add an extra layer of protection.

Using Moisture Barriers

Installing moisture barriers can help keep water vapor from permeating into the attic space. These barriers are especially useful in climates with high humidity or for homes in areas prone to heavy rainfall.

Smart Home Integration

Integrating smart home systems can also aid in mold prevention. Smart humidistats, sensors, and automated ventilation systems can monitor and control attic conditions in real time, issuing alerts if moisture levels become problematic.