Introduction
You’ve likely heard the term “dry rot” spoken with concern by contractors and homeowners alike. But what exactly is it? Contrary to its name, dry rot is not a condition of dry, old wood. It is an aggressive, wood-destroying fungus that requires moisture to survive. Understanding the science behind this destructive organism, known as Serpula lacrymans, is the first step toward effectively protecting your home from the significant structural damage it can cause.
This page will break down what dry rot is, how it lives and spreads, and why it poses such a unique threat to homes, especially here in the Pacific Northwest.
The Culprit: Meet the Fungus Serpula lacrymans
The term “dry rot” specifically refers to decay caused by one particularly virulent fungus: Serpula lacrymans, which translates to “weeping serpent.” This name is fitting, as the fungus’s thread-like structures spread silently and can produce teardrop-like moisture droplets.
This fungus is a member of the “brown-rot” family. It targets and digests the cellulose and hemicellulose in timber—the very components that give wood its strength and structure. By consuming these elements, it leaves behind a brittle, hollowed-out shell of wood that has no structural integrity.
The Four Stages of the Dry Rot Life Cycle
Dry rot evolves through a distinct four-stage life cycle, moving from a single spore to a massive, destructive organism.
- Spore Stage: It all begins with a microscopic spore. Spores are ubiquitous in the atmosphere, inside and outside your home, waiting for the right conditions to germinate. They are harmless until they land on a suitable food source with enough moisture.
- Hyphae Stage: When a spore lands on timber with a moisture content of 20% or more, it germinates and produces fine, white fungal threads called hyphae. These threads are the engine of the fungus, burrowing into the wood and releasing enzymes that break down the cellulose into food.
- Mycelium Stage: As the hyphae grow, they weave together to form a larger body known as mycelium. This often looks like a patch of white, cotton-like or grey, web-like growth. The mycelium’s primary goal is to expand and find more wood to consume. In its search for food, it can spread with surprising speed.
- Fruiting Body (Sporophore) Stage: Once the infestation is well-established, the fungus creates a “fruiting body.” This is a fleshy, mushroom-like growth that can range in color from grey to a deep orange or ochre. Its surface often has wide pores that release millions of new spores into the air, aiming to colonize new areas of your home. If you see a fruiting body, you have a mature and serious infestation.
The Critical Role of Water
It’s the great misnomer of home repair: dry rot needs water. The name comes from the dry, crumbly condition it leaves the wood in after it has feasted. To start growing, the fungus needs a source of moisture, such as:
- A plumbing leak
- A leaking roof or gutters
- Penetrating damp from outside
- Condensation from poor ventilation
Once established, however, Serpula lacrymans has a unique and dangerous ability. Its mycelium can transport water from the initial damp area to attack dry, sound wood elsewhere. This is why it can spread so far from the original problem spot.
Is Your Home at Risk?
Understanding what dry rot is makes it clear why it’s such a threat. It actively seeks out and destroys the core of your home’s structure.
- To learn how to spot the warning signs, see our detailed guide to the Signs of Dry Rot.
- To understand why it’s so common here, read about the Causes of Dry Rot in the Pacific Northwest.
- For a complete overview of our treatment process, please visit our main Dry Rot Repair page.
If you suspect any part of your home has been compromised, don’t hesitate. A professional inspection is the only way to confirm the presence of dry rot and prevent further damage.