Much like windows many homes have entry doors with rotted or soft spots down at the bottom of the jamb on either side. It is actually surprising to walk around a home that’s 10 years old or more and not find a rotted door jamb or two. It may even be a more common problem than rotting windows. Door jambs will usually rot within 6-8 inches of the bottom near the threshold. There are two main reasons for this; older door units have all wood jambs and many of them were not properly primed prior to painting and/or the fact that door jambs are vertical means all the water runs down to the bottom so it stays wet longer. Water can also leech into the end grain of the bottom of a door jamb where it meets the threshold. When wood stays wet long enough eventually fungus will begin to grow into it.
The first method of repair for minor damage is to dig out all of the soft wood and fill it with wood filler or bondo. I do not consider this a long term repair nor is it my first choice, however when budget constraints are a factor it is an acceptable short term band-aid fix.
The second and much more thorough method for repairing a rotted door jamb is to cut it off just above where the damage stops and splice in new wood or PVC. This is a much more long term fix than the bondo patch. The only drawback to this method is that a splice is almost impossible to do in such a way as to not be visible or noticeable. Basically I am saying you will most likely be able to tell that it was spliced or repaired . There are many instances when this is really not a big factor in the scope of the repair. This fix is usually employed when the damage is a bit worse and filler is not an option.
The last resort and definitely the best fix is to replace the entire door unit with a new one, which includes door and jamb. New door units come with PVC brick moulding(exterior trim) and no interior trim so when replacing a unit the interior trim has to be removed and new trim installed. Once installed I like to use the urethanized lifetime caulk that stays flexible and a good high quality bonding primer prior to painting. In my mind the biggest and best feature of the new door units available currently is the frame-saver jamb. These are an awesome invention…….the bottom 8-12 inches of the jamb is a composite material that is ROT-PROOF!!
When budget is not a limiting factor it is easy to see why a new door unit is the best choice for the long haul. The door in the photo above has a pretty badly rotted jamb and this is definitely a candidate for replacement. This one has been let go for way too long!