Flat Roofs
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FLAT ROOFS

Design Types. Flat roofs are not actually flat; they have a low slope to them. They come in three basic designs:

1. Built-Up: Asphalt based; multiple layers bonded together with asphaltic adhesion. Can be installed using hot asphalt, cold adhesive or heat welded (torch). Surfaces available are: loose gravel, mineral cap or a coating. Systems vary from 2 to 4 plies, which affects the availability of a product warranty.

2. Single-Ply: Made of various chemical compounds including PVC, TPO, EPDM and others. These are a single layer of roof covering (as opposed to Built-Up). Within the generic types, many chemical variations are available, changing the performance of the single-ply roof covering. Some are more fire-resistant than others; a significant difference is those that sustain flame and those that do not. Many single-ply products are recommended for “ponded water conditions”. A great deal of caution should be given before acceptance, as ponded water has a weight factor and can create habitat for insects and plants on the roof.

3. Liquid Applied: The most common types are: Acrylic, Asphalt Emulsion and Spray Polyurethane Foam. They differ somewhat in application and in performance. Asphalt emulsion and Acrylic overlays require little maintenance but SPF needs more frequent inspections and must be re-coated before the foam is exposed to the weather.

Maintenance. Because of their low slope, flat roofs generally require more maintenance than steeply sloped roofs. Water runs off very quickly from high-pitched roofs and has little opportunity to penetrate the roof or damage the roofing materials. Flat roofs, on the other hand, must be “bathtub” watertight to resist water penetration while the roof is draining from a heavy rainfall. In addition, after a rainfall there will be pockets of standing water on the roof. Over time, standing water will break down roofing materials. As a result, flat roofs often have shorter lives and require more maintenance than pitched roofs.

RECOMMENDATION: Flat roofs should be inspected annually for any signs of damage and touched up as needed to keep them watertight. Article submitted by Carl Brown, General Manager of AWS Consultants Inc.

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Adams Stirling PLC