Used mostly on roofs with no to very low slopes, tar and gravel roofs, also called built up roof or hot mopped is made by alternating layers of asphalt, tar paper and adhered with molten asphalt. Then a top layer of gravel is applied, some of which gets embedded in the hot asphalt and some stays loose on the surface of the roof. The layer of gravel to help protect the solvents in the asphalt from evaporating in the sun. The gravel is an excellent fire retardant, but it can clog drains and gutters.
If maintained, a tar and gravel roof has the life expectancy of 15 -20 years. Look for cracked and brittle areas as well as large areas of missing gravel when inspecting your roof for signs of damage.
Check local codes for how many layers acceptable
Some suggest removing an old tar and gravel roof before laying on a new one. The rough surface of an old roof puts the new roof membrane at risk of being punctured when walked on. If you decide to clean off the loose debris from your damaged roof instead of doing a tear off, you can apply another layer of felt, tar and gravel to be installed directly over an old roof; generally up to 3 roofs can be applied.
Tar and gravel roofs are generally the least expensive of the roofing materials for flat roofs. It is a smelly, messy job and not recommended for do it yourselfers. You will want a local roofer with experience in tar and gravel roofs.
