How to Identify Different Types of Wood Rot

There are two main types of wood rot that can infect your home. Not only is wood rot unsightly, it can cause serious damage to your home’s wooden structures. Before you can decide what to do about any wood rot you see, you need to be able to identify it. Learn more about the different types of wood rot—which are wet rot and dry rot.

1. Wet Rot

Wet rot is a common type of wood rot that appears on wood in highly damp areas. Wet rot comes from fungal growth, just like dry rot. Several different types of fungi can cause wood rot. The wet rot fungus attacks the cellulose or lignin in the wood, causing it to become weak and soft. When the wood has a constant moisture content of 30% or more, wet rot could form. It can grow in areas including:

• Damp basements

• Near leaking plumbing

• Under floorboards

• Around leaky windows and doors

• In areas where rainwater collects

• Areas in constant shadow that rarely dry out

What Does Wet Rot Look Like?

Wet rot goes through a few different cycles as this type of wood fungus grows.

• It starts as hyphae, which are white or brown strands that resemble spider webs as they grow across the surface of the wood.

• As the hyphae grows larger, they look more like white skin over the wood.

• Eventually, larger growths appear that resemble off-white-colored mushrooms, called mycelia.

• If left unchecked, the mycelia can migrate onto nearby non-wood surfaces.

• The wood itself may change color, becoming darker or lighter, as the damage takes hold.

Because wet rot frequently occurs in dark, damp areas, it can be difficult to spot. You should notice a damp or musty smell near the wet rot before you see it. The hyphae and mycelia do not emit an odor, but the dampness present in the area causes the distinctive smell. 

How Wet Rot Affects Wood

You can think of wet rot as eating away at the wood. With wet rot, you’ll notice soft rot in the wood. You can often insert a butter knife into the wood or use the knife to peel the damaged wood. With healthy wood, a butter knife would not be able to penetrate it.

As the wet rot continues unchecked, it breaks down the structural integrity of the wood, eventually causing cracks or collapse. 

Is Wet Rot Dangerous?

The various fungi associated with wet rot don’t cause health problems for most humans who inhale the spores, although some people are sensitive to these spores.

The most dangerous aspect of wet rot is its ability to spread to other materials and pieces of wood. As it spreads, it establishes itself and continues to weaken other sections of wood. If it weakens a key structural beam made from wood, it could cause the structure to collapse.

If you notice wet rot, call a local water damage restoration specialist to help remove damaged areas and make repairs.

2. Dry Rot

Like wet rot, dry rot is a type of wood rot that comes from a fungus. Only one type of fungal spore—Serpula lacrymans—can cause dry rot, though. Despite the name, dry rot requires some moisture saturation in the wood before it can begin to grow, usually about 20%. The dry rot fungus cannot grow on wood that is not somewhat damp when the fungus spores land on it.

What Does Dry Rot Look Like?

At first, dry rot looks like furry and white-colored hyphae growth. You may see a fine brown or orange dust in the area, which indicates spores.

In the next stage, the dry rot growth resembles a mushroom, called the mycelium phase. It often has an orange or red color like you’d see on a piece of rusting metal. If the dry rot occurs in wood with less moisture, the mushroom-like structure may appear light gray or off-white with tinges of yellow or purple instead.

Areas where dry rot frequently appears include:

• Floorboards

• Skirting

• Joists

• Beams

You should notice a damp, musty odor in areas where dry rot is occurring.

How Dry Rot Affects Wood

The fungus associated with dry rot digests the wood, causing it to weaken and suffer visible damage through the breakdown of its cellulose and lignin. When dry rot damages wood, you should notice areas becoming:

• Brittle

• Darker

• Dry

• Flaky

• Fragile

• Warped

Dry rot grows aggressively. It will spread across drywall and plaster in search of more wood. It’s also difficult to eradicate without the help of a professional.

Its aggressiveness means you should treat it as soon as you notice it. To repair dry rot, you need to completely remove the affected wood and bring in new wood. Add ventilation to the area to eliminate moisture. Using a wood preservative on the remaining wood or adding pressure-treated wood can reduce the risk of dry rot returning.

Is Dry Rot Dangerous?

The primary danger of dry rot is its ability to weaken structural wood. When beams or posts that are supporting weight have a dry rot infestation, they could fail, causing significant structural damage.

Dry rot fungal spores are not dangerous for most humans exposed to them. However, some people may be sensitive to inhaling the spores.

Types of Wood Rot Compared: Wet Rot vs. Dry Rot

Because dry rot spreads more aggressively than wet rot, it’s helpful to understand the differences between the two. However, trying to identify which type of wood rot you have is challenging. Wet rot and dry rot are very similar in early appearance, where they grow, and how they spread. 

If you see mushroom-like structures on the wood, the color of the material can be a key clue. Wet rot often produces small white structures, while dry rot structures are large and resemble a rusty color.

The affected wood provides a clue, too. When wet rot affects wood, it often becomes soft and spongy, while dry rot makes the affected wood dry and brittle.

Only one type of fungus, Serpula lacrymans, causes dry rot. Many types of fungi can cause wet rot.

If you believe you have either type of wood rot—or if you’re simply unsure—you’ll want to contact a professional as quickly as possible to inspect the damage and repair it.

Wood Rot vs. Mold

Both mold and wood rot are types of fungi that form in areas with varying levels of dampness. The difference is that wood rot causes the wood to deteriorate, while mold grows on top of the wood. When considering water damage versus mold, they both can cause discoloration on the wood, but they don’t necessarily cause structural damage. If the water damage saturates the wood for a long time, though, it could lead to wood rot.

Signs of mold in the house differ from signs of wood rot. Mold often looks like dark-colored or fuzzy patches or splotches on all kinds of surfaces. Wood rot starts as a spider-web-like growth before eventually resembling mushrooms. It primarily grows on wood.

Health-wise, mold is the more dangerous type of fungus because inhaling its spores can cause serious illness. If you have black mold versus white mold, the health risks with black mold are greater. Wood rot fungal spores are not dangerous for most people to inhale.

If you’re unsure whether you’re seeing mold or wood rot growth, you should reach out to a local mold inspector for a test.