Built Up Roofing Systems have good waterproofing characteristics but suffers from a loss of ductility after prolonged exposure to UV. Oxidation produces a chalk-like residue, cracking and alligatoring inevitably follows, allowing water to penetrate the system causing blisters, cracks and leaks.
There are built-up roof systems out there that are approximately 100 years old. They are long lasting and can last even longer with roof coatings. Coal tar built-up roofs have a life expectancy of 25 to 30 years, even more if maintained properly. An asphalt built up roof can last at least 20 years.
Roof coatings prevent premature deterioration in aged built up roofs. If done early, before any asphalt degradation and leaks, it can extend the life of your roof indefinitely. Otherwise, it can be costly to repair the roof to return it to good condition.