TPO is a good default for most homes because it’s reflective, its seams are heat-welded and it lasts about 20 to 30 years. EPDM costs less and works well on simple shapes. Modified bitumen is tougher underfoot, so it’s a good fit for decks and roofs people walk on.

Most last about 15 to 30 years depending on the material, how well it drains and how carefully the seams and flashing were done. A flat roof that holds standing water wears out much faster.

Ponding is worth watching. Water that sits on the roof works its way into seams and adds weight. Small puddles that dry quickly are common, but large areas that stay wet for days usually mean the roof or decking has sagged and should be corrected.

A single leak at a seam or flashing can usually be repaired. If the membrane is cracked or blistered in many places, water has soaked the insulation or decking, or the roof keeps leaking in new spots, replacing it is usually the better value.

Not on a roof that’s nearly flat. Below a slope of 2 inches per foot, shingles can’t shed water fast enough and will leak, so those sections need a membrane or a metal roof made for low slopes.

Light foot traffic for maintenance is fine on most membranes. If you plan to walk on the roof often or use it as a deck, tell us during the inspection, because modified bitumen or a walkway pad holds up much better than a bare single-ply membrane.