Wood rot can happen to any home, especially in the trim. These are by far the most susceptible areas to fungal rot, because they are the most likely to get a lot of moisture and heat. In some cases, you may just want to replace the damaged trim altogether. In others, it may be worth it to perform a relatively simple repair job using a two-part epoxy.
Find the Rot
This is relatively simple. Areas with bulging paint, peeling paint, or darkened wood may be rotting. Trim over windowsills or anywhere else where water is less able to drain are good places to look, as is anywhere low to the ground. A screwdriver will tell you all you need to know: press it into the wood and see if it depresses easily. If it does, you have some rot to root out.
How to Repair Your Trim
First, gouge away all the rotted wood with the back of a hammer or something similar. Once you have done that, use a smaller rotary tool (like a die grinder) to get rid of all soft wood. This is essential, since the epoxy will not bind properly with the moisture.
You might consider first putting a fungicide on or injecting a wood preserver into the damaged area. Either way, you're going to apply the epoxy primer, a thin liquid, to the entire area you are filling. This will allow the material to bond to the wood. After 15 minutes or so, the primer will have penetrated the wood enough for you to wipe the excess away and start the next step.
Mix the resin and the hardener (the two parts of a two-part epoxy) together on a plastic board with a putty knife. Fill in the hole, using the putty knife, and shape it to fit the missing trim. You will have 30 to 45 minutes before the material is no longer workable.
Give the epoxy a day to harden before sanding it down to blend with the trim (use coarser grit for the initial work and fine-grit for the details). Then, prime and paint it (acrylic works well) and you're finished!
Now that your trim is repaired, you won't have to worry about that rot spreading to other parts of your home. Isn't that great?