What Causes Wood to Rot?


One of the items that pops up in conversation most frequently when having a discussion with someone about painting the exterior of their home, is rotted wood.


Obviously, rotted wood is not something that you want to paint over, it is something that should be addressed in one way, shape, or form.

Perhaps the situation is one where the rotted portions can be carved out and then some type of epoxy system can be put in place, shaped, and prepped & painted.

The situation may also call for an actual replacement of the piece of wood that is rotted.



As these possible solutions are being worked through, part of our conversation may center around what causes wood to rot in the first place.



This is an excellent question.

Wood rot itself is a form of decay.


What sets off the decay is prolonged moisture exposure combined with fungi (microscopic organisms).


In order for the fungi to get comfortable and start rotting things away, the wood must be continuously damp.


Fungi will not grow on wood that is dry, it just won’t happen.


There are countless types of fungi that exist all around us, there is no way to really get away from them.



My experience has witnessed that wood often rots from the inside out.

In other words, you could have a piece of wood trim that appears perfectly solid one day, and then a few months later the wood seems to have rotted to the core.


The reality of the situation is that this did NOT happen overnight; instead the wood had gradually been rotting from the backside toward the front, until one day it finally broke through the front side of the wood and veered it’s not so pleasant face.



So, how does this type of thing happen where the wood gets wet without someone even knowing?

Actually, fairly easily…

Water does not need that much space to begin

gradually creeping in and starting to hang around a while.

As one example, when water is able to get through the inside crevices of wood trim, it is usually able to nest in an area that will not allow it to easily dry out, hence the reason these dark areas can become an attractive place for fungi to come on board and start doing their thing.

Preventing this from occurring amounts to checking around the exterior of your home once or twice per year (I recommend once in the Spring & once in the Fall) to see if you can spot any signs of rot or any places where rot may be able to begin to stem from if not addressed.


Simple preventative measures fighting the possibility of rot taking place can go a LONG way, such as:

  • Making sure that the joints in your trim are properly caulked
  • Making sure there are no visible holes in your trim where water can rest
  • Making sure your gutter & downspout systems are properly functioning
  • Making sure to limit the amount of time wood trim sits in snow in the Winter or piles of leaves in the Fall
  • Making sure that flashing is properly in place where necessary
  • Making sure that the grading of your yard is such that it steers water away from the home
  • Making sure vegetation around the home does not rest directly on the home


In short, the more you are able to ensure the exterior of your home stays as dry as possible and any prospective areas of allowing water to creep inside are eliminated, the longer you will be able to enjoy not having to replace wood that has rotted away and potentially set you up for even larger repairs, if it is not caught and corrected as soon as possible.

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