A re-roof is the process of laying new product over your existing roof. Roof repairs will generally save you time and money, but in most cases a new roof is the best option. As a general rule of thumb, if the existing roof on is only one layer and there are no problems with the roof deck, a new roof is not necessary.
Re-roofs require less labor, material and necessary disposal compared to a tear off. This cuts down on money and time. However, if you are going to do a re-roof it is still important to consider the ventilation of your attic.
Most expert roofers will agree that re-roofing will not last as long as a tear off. When re-roofing, the life span of the roofing singles is approximately 25% less than if you were to go with a tear off.