Wood rot fungi are microscopic organisms that consume the structural components of wood, leading to its decay. These fungi break down complex wood molecules like cellulose and lignin, returning nutrients to the soil in natural environments. When they infest wooden structures in homes, this natural process becomes a destructive force, weakening everything from floor joists to roof rafters. Their presence can compromise a home’s structural integrity, potentially leading to costly repairs if left unaddressed.
Types of Wood Rot
Wood rot falls into three main categories: brown rot, white rot, and soft rot, each with distinct effects on wood.
Brown Rot
Brown rot fungi primarily break down cellulose and hemicellulose. This degradation often leaves behind the darker-colored lignin, causing the wood to turn a dark brown and crack into cubical pieces, creating a cubical fracture pattern. While commonly referred to as “dry rot,” brown rot still requires moisture, specifically a moisture content above 28-30%, to initiate and spread.
White Rot
White rot fungi break down all major wood components, including lignin, cellulose, and hemicellulose. This results in a bleached, whitish appearance, and the wood often takes on a stringy or spongy texture. White rot is commonly found in hardwoods and can lead to substantial weight loss in the wood.
Soft Rot
Soft rot fungi can degrade cellulose, hemicellulose, and even lignin, though their primary focus is often cellulose. It is typically found in wood exposed to very wet conditions, like wood in direct contact with soil. Soft rot often leads to the formation of microscopic cavities within the wood cell walls, and while it can cause darkening and cracking parallel to the grain, the decay progresses at a slower rate compared to brown or white rot.
Identifying Wood Rot
Early recognition of wood rot can prevent extensive damage and costly repairs.
Visual Inspection
Look for any discoloration such as darkening, bleaching, or a grayish tint on the wood surface. Cracking, shrinking, warping, or peeling/blistering paint also indicate decay, often signaling trapped moisture. Visible fungal growth, appearing as cotton-like mycelium, thread-like strands, or even mushroom-like fruiting bodies, directly confirms the presence of active rot.
Tactile and Olfactory Signs
Tactile and olfactory signs also provide evidence of wood rot. Pressing a screwdriver against the wood can reveal a soft, spongy, or crumbly texture. If the tool penetrates more than 1/8 inch, the wood is likely rotting. A distinct musty or earthy odor is another strong indicator, resulting from the fungal activity breaking down wood fibers, and this smell is often more noticeable in enclosed, poorly ventilated areas.
Common Locations and Conditions
Wood rot often occurs where moisture accumulates. Basements, crawl spaces, and attics are common due to trapped humidity. Areas around windows, doors, and plumbing fixtures are also susceptible, as are outdoor structures like decks, fences, and any wood in direct contact with the soil. For wood rot to thrive, it requires three main conditions: a moisture content above 20%, suitable temperatures typically between 60 and 90 degrees Fahrenheit, and the presence of oxygen.
Preventing Wood Rot
Proactive measures prevent wood rot and preserve structural integrity.
Moisture Control
Controlling moisture is a primary defense. This includes proper drainage around foundations to direct water away from the home. Promptly fixing leaks from roofs or plumbing is important, as persistent moisture creates ideal conditions for fungal growth. Improving ventilation in damp areas like basements and crawl spaces helps reduce humidity levels, further inhibiting decay.
Protective Coatings
Protective coatings on exterior wood surfaces form a barrier against moisture. High-quality water-repellent sealants, paints, or stains reduce water absorption. It is beneficial to seal not only the exposed surfaces but also cuts, joints, and end grains, and even the back sides of boards, where water might otherwise penetrate. Regular reapplication of these finishes helps maintain their protective effectiveness over time.
Construction Practices and Maintenance
Proper construction practices prevent rot. Wood should ideally not be in direct contact with soil, and if it must be, using pressure-treated lumber infused with preservatives offers enhanced resistance to rot and insect damage. Ensuring adequate airflow around wooden elements, such as leaving appropriate spacing between deck boards, allows for better drying. Regular maintenance, including cleaning gutters to prevent overflow and trimming shrubs away from structures to improve air circulation, also helps keep wood dry and reduces the risk of decay.
Treating Wood Rot
Treating existing wood rot begins with a thorough assessment to determine the extent of the damage.
Removal of Damaged Wood
Remove all visibly rotted wood using tools like chisels, saws, or scrapers, checking surrounding areas for hidden decay. Remove all loosened material until only healthy wood remains. For severely damaged structural components, replacement of the entire piece of framing may be necessary, while smaller areas might be repaired with wood hardeners or epoxy fillers.
Moisture Elimination and Drying
Eliminating the moisture source is the next important step, as fungi cannot survive without it. This involves fixing leaks, addressing condensation issues, and ensuring proper drainage and ventilation. Once the moisture source is addressed, the wood and surrounding environment must be thoroughly dried. Drying may take several days, and moisture meters can be used to confirm that timber moisture content is below 20-28%.
Fungicidal Treatment and Prevention
Apply fungicidal treatments, like borate-based solutions, to remaining sound wood to kill active fungi and prevent future growth. Apply these treatments generously to affected and surrounding areas, including hidden cavities. After treatment, the area should be allowed to dry completely. Finally, re-applying preventative measures, such as sealing wood, improving ventilation, and maintaining gutters, helps ensure the problem does not recur.