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What Is Dry Rot?

Dry rot is a term used to describe wood decay caused by fungal infections. Fungi are microorganisms that eat organic matter and absorb moisture to survive. Wood, an organic material, is a good source of nutrition for many fungal species. Dry rot eats away at the wood on a microscopic scale, devouring the cells and weakening its overall structure as the infection overtakes the wood.

Outdoors, wood can defend against dry rot thanks to the bark, which is used as a protective shield so that the tree’s inner structure is safe from harmful elements. In your crawl space, however, the wooden joists and support posts have no protective shield. They are exposed to humidity, dirt, and bacteria, which is why they get infected with dry rot so easily.

What Does Dry Rot Look Like? 

Identifying dry rot in your crawl space will allow you to act against the infection and protect your wood from structural collapse. Depending on how advanced the fungal growth is, you may or may not have a challenging time identifying dry rot on the wood in your foundation. This is because dry rot can be incredibly damaging in its initial stages while also being very subtle.
In its early stages, dry rot starts as spores. Spores are fungal cells that have yet to mature. Individual spores are microscopic, but if enough of them accumulate in a single spot, they look like red, brown, or orange dust. The immature spores will only grow if the environmental conditions are conducive. The temperature, oxygen, and humidity levels need to be precisely correct, and there needs to be a lack of sunlight. Once these conditions are met, the spores grow hyphae, white, individual strands that the mold cells use to grow and spread. A collection of hyphae is called mycelium.
Mycelium is the bacterial colony that appears as fungal growth, slowly consuming wood. It is white, mossy, and feels like cotton, though it can look like sticky mucus on the wood. Sometimes, it can go from white to a light tan as it gets exposed to dirt and other bacteria. The fungus cannot reproduce at this point, so removal of the dry rot during or before this stage is more accessible.
The final stage of development is a fruiting body, which appears once the fungus is mature and can release spores into the air. The fruiting bodies on the wood look like mushrooms with a red center, and it’s from this red center that the spores get released. The airborne spores land on a viable living surface and then, if the conditions are right, will begin to grow, and the cycle starts again.
Aside from the hyphae strands, mycelium cluster, and the fruiting bodies, dry rot damages the wood in another visible way. Because the infection is breaking down the wood, specific patterns may be visual after the infection has taken over. Wood will begin to crack, break, and flake off when decaying. The cracks will interconnect and form rectangular patterns on the surface of the wood.
Dry rot is sometimes confused for termite damage because of the way it breaks down after infection. If you’re unsure whether your crawl space wood is breaking down due to termites or dry rot, contact your local foundation experts for an inspection.

Thats the million dollar question! Unfortunately, we won’t know for sure until siding is torn off.

First, you need to understand what “dry rot” is. The name is misleading, except that infected wood becomes brittle and crumbles when dry.
Dry rot is a fungus. In dry conditions, it is dormant, but if there is moisture available and the temperature is warm enough (and that only means “cool” in terms of weather conditions, not “hot”), it will become active and start to reproduce.
It reproduces and spreads in two ways: it forms fruiting bodies that look like small brownish “mushrooms” about the size of your thumbnail, producing spores dispersed by the wind, exactly like most other “mushrooms.” The second way is to grow threads within the wood itself. Those threads can develop unseen and produce several inches daily in the right conditions. If you do see them, they look somewhat like the trail of mucus from a giant slug or snail, and you might not consider they had anything to do with the “dry rot” at all.
When it is active, it produces a characteristic “rotten wood” smell – though if it is outdoors, the wind may stop you from noticing that.
There are three ways to contain the problem. The best way is to remove all the contaminated wood physically – and because of the threads, that can be more than the parts that appear crumbling or “rotten.” To do that effectively, you need to sterilize any cutting tools. Otherwise, you are just implanting fungus spores in the freshly cut surfaces. You must also treat all the cut surfaces with a suitable fungicide since the wind can blow in more spores.
The following best is a chemical treatment to kill it, but that can be problematic because it’s hard to know if you have killed “everything.” Most likely, the infected wood was already treated with chemicals before it was used for building, but over time, that treatment stopped working or leached out of the wood. The only way to treat wood thoroughly is by immersing it completely in a fungicide solution under high pressure, forcing the solution into the grain structure of the wood rather than just coating the surface.
The least reliable way is to remove any possible water source and attempt to keep it permanently dormant. The problem is that if you are only 99% successful in doing that, you have just hidden the problem from view while it will continue to develop.
If the fungus gets into the structural parts of the wood framing, that is a much more severe problem than the superficial damage in your photos – but unless you remove the damaged siding, there is no way to tell if that has happened.

Many people need help maintaining their beautiful exterior woods in our harsh climate. The difference between our company and other companies is that we do restoration and follow-up with cost-effective maintenance.