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Posted by on Dec 4, 2016 in Tell Me Why |

Why Does Wood Rot?

Why Does Wood Rot?

Wood rots or decays because it is an organic substance – that is to say, it is a living thing – made up of tiny box-like units called cells. Like any living things these cells can die. The attacks of insects and the growth of fungi are two of the most common causes of decay.

In leaves or flowers the cells are often square or rounded in outline. But in timber or wood they are mostly long and narrow, for they have to serve as tubes to carry sap from the roots up the tree trunk. Their walls are strong and fibrous because they have to support the weight of the branches and leaves above them.

They interlock to form the wonderfully strong and pliable substance which we know as wood. The cells do not continue to carry sap for the whole lifetime of the tree, because the trunk and boughs grow larger and soon contain more cells than are needed.

So the inner part of the trunk and branches ceases to carry sap, and the cells gradually fill up with gums and resins which make them stronger, harder and better able to resist decay and rot.

When wood is cut the cells are full of watery sap. This timber is stacked in the open air for several months, or in a special drying room, called a kiln, for several days. It is then “seasoned” and ready for use.

The 4 conditions that must be present in order for wood rot to occur:

  1. Substrate (Wood)
  2. Oxygen
  3. Warmth
  4. Moisture

Fungi, the simplest of all plant life is the one thing that causes rot. Microscopic fungus spores are all around us floating on the breeze and landing all over our homes. Wherever they land, if the 4 conditions above are present then you will have rot and that rot will continue as long as those conditions are present. Even if you remedy the conditions the fungus is still present and will resume growth (aka rot) when the conditions are more favorable.

How to Stop Rot

brooklyn bridge

So how do you stop wood rot? Well, you can always remove wood from the equation but for most of us that would mean remove our entire house. And here on earth there isn’t much we can do about eliminating oxygen or warmth.

On a side note, the lack of oxygen is why wood that is submerged underwater for decades or centuries can remain in completely pristine condition. The organisms that cause rot need oxygen to survive and the underwater environment is decidedly oxygen free. The city of Venice, Italy and the famous Brooklyn Bridge are a couple examples of structures built of wood foundations that have survived hundreds (and in Venice’s case thousands) of years with no trace of rot.

Back to how to stop rot. If we can’t get rid of wood, oxygen or warmth then the only thing we’re left with is moisture. So then, how can we stop the wood elements of our house from excess moisture which causes rot?

Let it Dry

It is going to rain or snow and the wetting of your house is not a cause for concern. The concern is when wood isn’t able to dry out. There are a few things you can do to help the wood on your house dry out.

  1. Keep it Painted – Keeping your house painted is the easiest way to keep the water out. Paint is a great layer of protection to help the surfaces of your house shed water and dirt. Though it may get wet the paint keeps the water (and fungus) from attacking the underlying wood.
  2. No Standing Water – If any part of your house gets standing water after a rain storm then that area is much more likely to rot. Standing water will find its way into joints and cracks in the paint and seep into the wood giving rise to perfect conditions for rot. Redesign these elements to allow water to shed off of them.
  3. Allow For Air – Good airflow helps everything dry out faster and the faster things dry the less chance of rot. Trim back shrubs and trees from your house so that there is a enough room for some airflow between the two. Wet shrubs directly against siding are a major cause of rot on many houses.

If you can keep it dry you’re leaps and bounds ahead of the rest of us. Yes, the cause of rot is fungus, but if you focus your energies on keeping the exterior surfaces of your house dry you’ll stop it in its tracks. And preventing rot is a lot easier than stopping it once it really gets rolling.

Content for this question contributed by Bill Hickman, resident of Portsmouth, Virginia, USA