All roof membrane types have general lifespans. For example, EPDM and TPO roofs last about 10 to 20 years. Multi-layer BUR membranes last about 15 to 20 years, while BUR membranes with three to five layers often last about 10 to 15 years. If your building has one of these three membranes and the membrane is within the range listed for its roof type, you should consider replacing your roof. However, your commercial roof may need replacing before then for other reasons. For instance, your roof may need a replacement if it has sustained major damage in the wake of a severe storm. If your roof has extensive damage and you don’t know whether it needs repairs or a replacement, use this rule of thumb: Talk to your contractor and figure out how much the repairs will cost, then compare those costs to the cost of a roof replacement. If the repairs cost more than half as much as a replacement does, choose the replacement.