Wood Decay and Wood Rot Fungi: The What, the Where, and the Why
- By: Dr. Chin Yang
- Tags: Mold and Fungi, Wood Decay, Wood Rot Fungi
In December 2024, Pace® designated its laboratory in Pennsauken, NJ as a Center of Excellence for Fungal Analysis. Staffed by a team of expert mycologists and led by Dr. Chin Yang and Dr. Ching-Yi Tsai, our new COE provides a wide array of mold and fungal testing and analysis services to support our Building Services clients. In addition, the lab has added new test parameters, such as wood decay analysis.
While wood rot fungi are all around us and can be highly destructive, many commercial laboratories do not offer wood decay analysis. In this post, we explore wood decay and wood rot fungi: what they are, the problems they cause, how to identify it, and how to analyze the situation.
What is Wood Decay?
Wood decay is caused by a subcategory of fungi that can impact wood and wood-related materials. The decay caused by wood rot fungi is often referred to by its common name (white rot, brown rot, or soft rot), which describes the appearance the various species give to impacted wood.
White Rot: This type of fungi decomposes the lignin in the wood, giving it a whitish or light appearance. Lignin is an organic polymer found in the cell walls of wood that gives the wood its structure and rigidity. As the cell walls degrade, wood with white rot feels spongy and may look stringy.
Brown Rot: Brown rot primarily breaks down the cellulose in the wood, leaving a brown lignin residue. Wood impacted by brown rot fungi becomes brittle and crumbles easily, an effect commonly referred to as “dry rot.” This term can be misleading; however, as all wood rot fungi require moisture.
Soft Rot: Soft rot fungi tend to degrade wood more slowly than other types. Soft rot can lead to the wood having a honeycomb-like appearance.
Brown rot and white rot are of great concern in wood-structured indoor environments. Although soft rot is frequently detected indoors, it is more likely to negatively impact external structural features: wooden decks, windowsills, shingles, etc.
A related, less damaging effect of fungal colonization in wood by so-called sapstain fungi leads to dark staining on logs and lumber. This staining can be blue or black, lending the fungi the colloquial name “blue stain fungi.” While sapstain fungi mainly affect the aesthetic value and marketability of wood by changing its color, they do not significantly weaken the wood structurally.
Ideal Conditions for Wood Decay
Like other problematic mold and fungi, wood rot fungi are hydrophilic (water-loving), so all it takes for these fungi to grow is excess moisture, the right temperature range, and a food source—the cellulose, hemicellulose, and lignin found in the cell walls of wood. The moisture can come from a variety of sources, such as spills, leaks, flooding, or high humidity. Wood rot fungi can take hold quickly, generally within just a couple of days of the initial incident if the wood remains damp in the presence of spores. The wood rot fungi may continue to grow and, over time, weaken the structural integrity of the wood.
Like other fungi, wood rot fungi reproduce through sporulation (producing spores). When airborne, these spores can create respiratory issues in sensitive individuals. However, the structural damage these fungi cause is typically of greater concern. Some, like soft rot fungi, are slow growing. Others, such as Serpula lacrymans, grow more rapidly and spread easily, so early detection is critical to limiting structural damage. In addition, wood rot fungi can also impact the value of a building by giving it a musty odor long before structural integrity becomes an issue.
It’s also important to keep in mind that wood rot fungi can impact a variety of wood-based building materials other than lumber. Examples include flooring, wood framing, corkboard, fiberboard, sawdust/cellulose insulation, and wallpaper.
Sample Collection and Analysis of Wood Rot Fungi
Wood decay can be detected visually through discoloration, softening, and other physical signs. However, wood decay is a slow process, and direct visual inspection cannot always determine the degree of wood decay and the extent of the damage. In addition, the air sampling often conducted during a home inspection cannot typically be used to detect wood decay or identify wood rot fungi because wood rot fungi may or may not produce identifiable fruiting bodies.
To gather sufficient information to assess the danger to the structure and inform remediation strategies, bulk samples (wood that may or may not already show signs of rotting) need to be submitted to the laboratory. Lab analysts then carefully examine the samples for physical strength, the degree of decay, and macroscopic and microscopic characteristics typical of the various types of wood rot and wood decay fungi.
To further aid in identification, expert mycologists may note characteristic growth structures. For example, rhizomorphs are large strands of “bundled” hyphae, which give certain species of wood rot fungi the ability to gather water further away from the colony. This allows the fungi to grow without a precipitating event, such as a leak or flood damage.
Any Questions?
Wood decay is all around us, but many people never give it a second thought. However, when it starts to erode the value of your facility or endanger your building’s occupants, wood decay can quickly become a serious issue. If you have questions on wood rot fungal analysis and how it can help you assess your risks, reach out to us.
