Builders use hot tar and gravel, modified bitumen, or a rubber membrane on homes with flat roofs. Homeowners can also pick a standing seam metal roof if they have a roof pitch of at least 1/4 inch per foot.
Hot tar and gravel roofs, also called built-up roofs, use layers of a waterproof membrane interspersed with hot tar and heavy gravel. While originally the waterproof membrane was tar paper, contractors now use fiberglass membranes, as of 2015. A built-up roof is the cheapest option, but it is heavy to install and difficult to locate a leak once it is in place.
A modified bitumen roof is a roll roofing that has one side permeated with minerals that protect against sun damage. Older modified bitumen roofs required that the installers heat the adhesive with a blow torch during the installation. Newer systems offer peel-and-stick technology that makes them easy to install for homeowners.
A rubber membrane roof, made from sheets of ethylene propylene diene monomer, is easy to install for do-it-yourself homeowners. It is also easy to patch and find the source of leaks. However, it is more expensive than other roofing options and cannot withstand punctures.
Standing seam metal roofs are the most expensive option, but they are the most durable. Most metal roofs have a 35-to 50-year warranty and can save homeowners up to 30 percent on energy costs related to heating and cooling.