What is Dry Rot?

Dry rot

In the event of a major flood or a broken water appliance in your home, the organism most likely to wreak havoc to the wood in your home will be the fungus commonly known as wet rot. As we covered in our previous article, wet rot can only infest wood that has a moisture content of at least 50%. This means that the only way a wet rot organism can really cause damage in your home is in the event of a broken water appliance, or worse, a major hurricane related flood. Any of those things could happen at nearly any moment, however, there is another fungal organism that is capable of causing an equal amount of damage that doesn’t require such catastrophic circumstances to thrive. This fungal organism is commonly known as dry rot, and as its name implies, it requires far less moisture to successfully infest wood.

What is Dry Rot?

Dry rot, whose scientific name is Serpula lacrymans, is a fungus that thrives in warm, humid environments, and therefore is a common nuisance here in Tampa, as well as throughout Florida. Much like wet rot, it lives inside of wood, however, unlike wet rot, it only requires wood that has a moisture content of at least 20% in order to thrive. In the wild, dry rot survives by breaking down old logs and branches, and any other dead pieces of wood it can come across. However, dry rot, like most fungi, is a very opportunistic organism, and it has adapted to be able to infest the wood products that are commonly used in our homes. Floorboards and ceiling beams are at risk. Mortar joints and pieces of plaster are at risk. Even the drywall and the wood panelling on hardwood floors are at risk. Even worse, if this fungus infects your drywall, it will actually destroy the electrical wiring in your home as it exudes digestive enzymes in order to break down the wood it is living in. These digestive enzymes are highly acidic and will actually break down the covering on your electrical wiring, and effectively render it useless. As one can imagine, dry rot is an extremely destructive fungus. However, it’s destructive nature comes not just from its ability to destroy wood in addition to electrical wiring, but also from its ability to cover large distances.

Dry rot’s ability to move large distances is done in one of two different ways. The first has to do with its reproductive part of its life cycle. Like most fungi, dry rot reproduces by producing hundreds of thousands if not millions of microscopic spores over its lifetime. These spores are so small that they are literally lighter than air, and so any breeze or gust of wind can carry them over immense distances. If one of these spores happens to land on or nearby any source of wood that has a moisture content of at least 20%, the spore will germinate, much like a seed. When the spore germinates, it produces several thread-like structures that travel outward radially in all directions. These thread-like structures are individually referred to as hyphae, and collectively they make up a string-like structure called mycelium. Once the spore germinates and produces mycelium, the mycelium will then penetrate the wood and grow throughout the inside of the wood. Inside the wood, the fungus exudes digestive enzymes that dissolve the wood into tiny particles of basic nutrients that the fungus then sucks up through the hyphae.

The second method dry rot uses to cover large distances is where its most truly destructive nature resides. When the nutrients in one piece of wood are totally consumed by dry rot, rather than die, the dry rot will actually go searching for new wood to infect. In a phenomenon that is highly unique among fungi, the dry rot mycelium will grow out of the infested, depleted wood, and grow in all directions in search of new wood to infest. Not only will the mycelium grow towards any sources of wood, but it also will grow towards any source of moisture as well. The dry rot will actually be able to channel water through the mycelium and use that water to infest wood that is not 20% saturated with water, but this only occurs with fully mature dry rot organisms. Dry rot is capable of travelling astonishing distances with this strategy. People have discovered dry rot that has infested one house, grown out of the house, under the sidewalk, under the road, across the street over to another house, and infested that house as well. This ability for dry rot to grow over large distances like this is enhanced by the presence of bricks or concrete, as these materials hold moisture on their surface, and they provide something akin to a ‘path’ for the dry rot to follow on its quest to infest.

How to Identify Dry Rot:

It’s crucial to be able to recognize dry rot when and where it occurs, as the sooner it is stopped, the less damage it will be able to do to the timber in your home. Any kind of fungal growth in your home is the first warning sign. The mycelium will be recognizable as white to yellow/lilac threads that are growing on the surface of any wood products, or any brick/concrete surfaces in the home. The type of wood is insignificant to dry rot, so both hardwoods and softwoods need to be inspected if you suspect your home has a dry rot infestation. Fully mature dry rot specimens will produce a brown/orange fungal growth on the outside of the wood it has infested. It will look like a mat of brown/orange fungus. This mat is where the mature dry rot specimen is producing its spores. If you discover dry rot at this stage, it is certainly too late to save the wood that it is growing on, and the wood will have to be replaced. Prior to this stage, you will see deep cracks in the wood, which is a result of the moisture in the wood being sucked out by the fungus. Finally, let your nose be your ally, as you will most certainly detect the smell of mushrooms anywhere near dry rot that has infested wood.

How to Treat Dry Rot:

The treatment of a dry rot infestation is very similar to the treatment of wet rot, which we have covered in our previous article. Essentially, the wood will have to be tested to determine whether it is structurally compromised and needs to be replaced. If the wood can be saved, it will be treated with a fungicide, as will any new wood that is installed. Professionals will attempt to identify the source of moisture that the fungus is utilizing, and much like wet rot, there is a chance that there will be a leaky appliance in the home that needs to be fixed. However, since dry rot doesn’t require a whole lot of moisture, and can thrive simply in a high humidity environment, it may be recommended that you utilize a dehumidifier or even upgrade your HVAC system to manage the humidity in your home more tightly.


In the unfortunate event of a dry rot infestation, there is a good chance that you will need to have your infested wood products replaced. Whether it’s the drywall, the mortar joints, the flooring, or the ceiling boards, we can help your restore it all here at Premiere Builders. We know how much of a headache such a scenario can be. After all, the scientific name Serpula lacrymans translates from latin into “The creeping tear maker”. To help you with your restoration woes, we always offer free estimates on any and all of our services.