Signs of siding that are beginning to go bad include things like fungus, separation at the seams, warping, and moisture appearing on the inside of your home.
Often, siding problems only affect a small portion of the planks.
This is particularly true for vinyl and aluminum siding, but can also be true for some wood siding installations as well.
In many cases, individual boards can be removed and replaced without disrupting the ones around them.
Keep in mind, it can sometimes be difficult to match color on the new planks to the old ones.