Although nothing compares to the expertise of Denver roofing companies , if you keep an eye on your roof on a regular basis, you might be able to tell when is the time to replace it, even without calling an expert.
The first thing that you should keep in mind is that the main factor that influences the lifespan of a roof is local climate. So, if you live in an area where the climate is rather harsh, you should expect your roof to deteriorate faster.
There are exterior signs that tell you when the roof is in trouble and should be soon replaced.
An isolated leak detected on time can be repaired, but these problems tend to be insidious, you may not realize you have them until it is too late and the damage is too big to be repaired. So, if your roof has been affected by moss and algae growth, the insulation has been damaged by moisture and you have water damage in the interior walls (mold etc.), it is definitely time for a re-roofing project.
Also, a roof cover that has been largely damaged by a severe weather phenomenon must also be replaced. A few broken or missing shingles can be replaced individually, but if the damage is more extensive and possibly extended to the roof structure, there is no excuse to postpone the roof replacement.
Finally yet importantly, you should know that it is time to replace your roof, when it gets close to the end of its lifespan.