The Best Resurfacing on a Flat Roof That Pools

Flat Roof Pooling

• All flat roofs need to drain, however slowly. If rain forms pools on your roof, you likely have an architectural issue that resurfacing alone will not cure. You need to give the roof a slope, or pitch, of at least 1/8-inch per foot so the water can drain. If your roof is small, you can make long wedges out of 2x4s and nail them to the roof joists to provide the necessary pitch. If your roof is large, a commercial roofing company can make a foam underlayment that will match your roof’s measurements and give it a slight slope.

Built-Up Roofing

• Overlapping rolls of coated felt or mats interspersed with layers of bitumen are called built-up roofing (BUR). Bitumen, otherwise known as asphalt, is made of distilled petroleum. BUR roofs absorb heat so you have to top them with a special reflective sheet or ballast. The ballast is usually crushed gravel, small, round river stones or pavers of concrete or tile. BUR roofs last 10 to 30 years. The reflective sheet or ballast makes inspecting roofs difficult; so if your roof pools with water, it will be difficult to check and maintain the seams. BUR is cheap and easy to apply, but it is also heavy and subject to puncture.

Single-Ply Roofing

• Special fasteners or plates are used to apply panels of single-ply roofing. The most commonly applied single-ply roofing is competitively priced, easy to apply, propylene diene monomer (EPDM) rubber roofing. Gray or white panels of polyvinyl chloride (PVC) are glued or applied with a blow torch. Laminates of ethylene propylene and ethylene polylene polymers, called thermoplastic olefin (TPO), are welded with hot air. These roofs cost more than BUR, but they last longer.

Spray Foam Roofing

• Several forms of polyurethane can be sprayed on flat roofs to form a single, seamless barrier. You can spray these foams directly over the existing roof and cover them with a thin layer of tiny crushed stones or sand. Polyurethane foam roofs are well insulated and easy to maintain, but you have to re-spray them every 10 years.