Brown Fungus on Wood: Causes, Risks, and Solutions

The appearance of brown fungus on wood surfaces is a common concern for property owners, signaling an underlying issue with excess moisture. This growth indicates that environmental conditions are favorable for fungal development. Understanding the nature of this fungus is the first step toward addressing the problem effectively.

Identifying Common Types of Brown Fungus

The most significant type of brown fungus is brown rot, often called “dry rot.” This fungus targets the cellulose in wood, causing it to darken, shrink, and develop a pattern of cubical cracking. This process leaves the wood brittle and easily crumbled into a dry powder. Severely affected wood may also produce visible fruiting bodies, which can look like mushrooms and release spores to reproduce.

You might also encounter slime molds, such as the chocolate tube slime mold. While they can appear as a brown, foamy, or slimy mass on wood, they are not true fungi. These organisms do not consume the wood itself but feed on bacteria, posing no threat to the wood’s structural integrity.

Causes of Fungal Growth on Wood

The primary cause of fungal growth on wood is persistent moisture. Brown rot fungi require a wood moisture content at or above 28%, which can result from plumbing leaks, roof leaks, or direct contact with damp soil. Poorly ventilated spaces that trap condensation also create this level of saturation.

Fungi also flourish in moderate temperatures, between 60 and 90 degrees Fahrenheit. High humidity, darkness, and stagnant air further contribute to an ideal habitat for fungal growth. Poor ventilation is a major factor as it traps moist air, preventing wooden surfaces from drying.

Assessing Potential Risks

The risks of brown fungus include structural damage and health considerations. Brown rot is a serious threat to wooden structures because it compromises the wood’s strength. This decay can occur invisibly within walls or floors, where a 10% loss in wood weight can cause up to a 90% loss in strength.

The spores released by brown fungi can also affect indoor air quality. While not as hazardous as some black molds, inhaling these spores can trigger allergic reactions, asthma attacks, and other respiratory issues in sensitive individuals. Symptoms may include headaches, coughing, wheezing, and eye irritation.

Removal and Prevention Strategies

For small, surface-level patches of fungus, cleaning with an appropriate solution may be sufficient. However, if brown rot has made the wood brittle, the affected material must be removed and replaced to ensure structural safety. A professional assessment is often recommended, as determining the full extent of the damage can be difficult.

Preventing future growth is dependent on controlling moisture. Key strategies include:

• Identify and repair all water sources, including leaking pipes or roofs.
• Improve ventilation in crawl spaces and bathrooms with fans or vents to reduce humidity.
• Use a dehumidifier to keep basements and other damp areas dry.
• Prevent direct contact between wooden structures and the ground to stop moisture wicking.