For low pitched roofs with a slope of less than 2:12, such as on contemporary homes and commercial buildings, tar and gravel is the most common built-up roofing material. It’s “built-up” because it is constructed of at least 3 layers of waterproof material that alternates with layers of hot tar. With a life expectancy of approximately 20 years, the gravel on top of the built-up layers serves to shield the roof from sun damage. Tar and gravel is not recommended as a DIY project, which is why Mainline Roofing offers expert installation services. Relax while we do the dirty work!