Typical Modern Flat Roof

Considerations

• Flat roofs don't shed rain and snow as easily as their more steeply pitched counterparts, so they're more often seen in milder climates. Flat roofing materials, however, have improved drastically in the last 20 years and today they're used in both commercial and residential applications. While they may have required frequent maintenance and repair years ago, today they are often guaranteed to last a couple of decades. Installers should pay particular attention to the seams and flashing to ensure the roof doesn't develop any leaks.

Built-Up Roof (BUR)

• The built-up roof consists of several different layers of material, often arranged on top of each other in a crisscross pattern until the desired thickness is achieved. Layers may be made up of tar paper, rolled asphalt or modified bitumen. Hot tar seals the layers together. Pea gravel or river rocks are often applied to the top of this roof, acting both as a ballast and a shield against the sun's damaging rays. Although a built-up roof is inexpensive to install, it's messy to install and not something the average homeowner can handle. This roof type is also heavy, sometimes requiring structural reinforcement.

Single-Ply Roofing

• Single-ply roofs are the most popular choice for flat roofs, due to its ease of installation and lighter weight. It combines a membrane and weathering surface together in one layer. Ethylene propylene diene monomer, EPDM, is one such material that's been around for years. This rubber membrane comes in 10-foot-wide rolls to minimize seams and installers can trim it with a simple utility knife. Polyvinyl chloridem, PVC, and thermoplastic polyolefin, TPO, are also used in some types of single-ply roofs. PVC roofs are typically more durable, while TPO roofs are less expensive. Both require a special machine to join the seams together. Modified bitumen can be used in single-ply roofing applications. This material is manufactured with a mineral-based wear surface. Peel-and-stick versions of modified bitumen roofs make installation easy.

Spray-On and Paint-On Roof Coatings

• Spray foam roofing offers added value because it provides some insulation. Installers apply the foam to the surface and then apply a layer of urethane or acrylic. A final layer of sand or fine stone protects the foam from the sun's rays. Animals can damage the foam layer, but it's easily repairable with exterior caulk. Paint-on roof coatings are applied to existing flat roofs. The coating acts as a seal, prolonging the roof's life. A paint-on coating must go on top of a smooth, clean surface. It isn't effective on a BUR roof, for example, but applying it to a EPDM roof might extend the surface's life.