When most people hear dry rot, they run for cover. Dry rot does to a certain degree deserve its fearful reputation. But if you understand it, it does lose some of its scariness.

Dry rot is a fungus, to be precise, Serpula lacrymans. Which means that it is part of the carbon cycle, taking the carbon that is contained in plant life (in this case timber) and returning some of it to the air as carbon dioxide, whatever the fungus doesn’t eat returns to the ground.

This is a completely natural process, however humans like to fight nature, so the key thing to remember is; if you don’t want dry rot, don’t allow the natural conditions. Persistent damp and stagnation around any sort of timber. If you have water food and stagnant air, fungus will grow.

 Dry Rot Triangle

Fire has a triangle, it needs heat, air and food to burn. If you take any of these things away the fire goes out. Dry rot like fire can spread through a building and cause a tremendous amount of damage, it just does it more slowly.

However as with fire, it has a triangle of needs to get going. Dry rot always starts with water (despite its name), a roof leak, pipe leak or just a damp area. However dry rot will only grow if there is timber (food) and if the area is lacking air flow (dry rot doesn’t like fresh air) as soon as you remove one or more of these conditions, it starts to die.

Dry rot does damage slower than a fire it also dies slower than a fire. In fact, it can take up to 10 years to completely die off.

It is for the most part simple to treat dry rot, although it is not always easy.

Most fungus found in buildings stays with the timber that it starts on, when it runs out of water or it has exhausted the nutrients in the timber it is living on, it just dies.

Dry rot isn’t like that.

Dry rot will put out “root like” mycelium, this can travel through brick work and other aggregate. It can derive water from this form of material, but it needs the nutrients in timber to survive. It is this ability to traverse materials other than timber that gives it its reputation, it goes looking for food!

The Need to Grow.

Another aspect of the fungus that makes it dangerous comes along with the conditions it needs to grow. As fresh air kills it, it is not going to start growing where there is air movement. Therefore it can grow undetected possibly for years, under floors behind paint and plaster until it decides it is time to reproduce.

At this point it will produce a fruiting body that pops up to the surface and it can quiet often be at this point, that it is discovered.

The problem with this is that by now it could have done considerable damage to the building. As the rot feeds on the timbers, it causes them to lose structural strength, yet on the opposite side of the timber, it can look perfectly fine. If it is in a floor, for example, you may find yourself dropping through it.

On Site

In Nuneaton we had a building with a nasty case of dry rot, it had been there for some time feeding on its timber windows and growing through its solid filled brick walls. A lot of its root like mycelium had become flat and cobweb like. Evidence that it had in places died off, however in other places it was very healthy looking.

The dry rot had fruited in the gents’ toilets producing a fine lair of red dust, because the spores are so fine, you would need 20 000 million (2×10 the power of 10) to cover a Square meter. It is because of its tiny size (each spore is only 0.01mm long), that is exists on or in most buildings to begin with.


This is the mycelium growing under the stairs landing. I had travelled through the wall from the toilet upstairs. It had found itself a nice spot in the space between the boards and the plaster lath ceiling.

This is the wall above the landing. In the foreground you can see the dead, flat cobweb like mycelium that is root like that traverse’s aggregate.

In the hole behind, you can see the whiter fluffier mycelium that is very much alive and is living off the nutrients that the main body of the fungus (above photo) is taking from the stairs.


The first thing we did was to attempt to limit the amount of exposure the rest of the building. This was done simple by keeping doors closed and sealed to other parts of the building.

The procedure to remove all timber, plaster and stud partitions began, until we got to clean brickwork and timbers. We continued to remove the dry rot until we were about a meter or more away from the last visible point of infection.

Sometimes the fungus can travel behind the brick work and pop up a bit further away; which is why you need to remove all timbers a minimum of 0.600m past the last visible point of infection.

We then replaced all timber with non-timber alternatives, so UPVC windows, steel stair case Etc. We have also left the brick work bare to prevent any growth reoccurring behind the plaster.

Finally, we treated all several times with a chemical treatment.

Chemical treatments are great as a preventative measure, however their effectiveness on an out brake is debatable. It does however help towards making an area a little less hospitable to the rot reoccurring after all available food sources have been removed.

More information

If you would like to know more about this subject there are several online sources that you can look at.

I found the book Decay of Timber in Buildings by C.R Cogins very helpful. It is published through Rentokil (at present out of print) libraries and second hand on line seller may have it.


Emily Millar