Flat Roofing Advice

Considerations

Using roofs for entertaining has been common since biblical times (Deuteronomy 22:8). Flat roofs use continuous membrane coverings, preventing standing water. Whether the flat roof is for living space or a green roof, there are maintenance issues to consider:

•Tar and gravel roofs do not resist pooling like a continuous membrane.
•When continuous membrane is not possible, use sealants and adhesives to adhere multiple membranes.
•Metal roofs, when seams are soldered together, make the most reliable flat roof.

Installing a green roof requires forethought and expertise. Determine what the roof's weight load is in addition to the standard snow load. Add together the weights of all the roof components and what a green roof installation will weigh, such as waterproofing, drainage, growth media and plants. Growth media may be pregrown plant mats or a multilayer buildup method. The weights of all components should not exceed the roof's weight load.

Before considering installation of a green roof, it must first be determined that the roof is damage free and structurally sound. Hire a professional roof consultant to make this determination.

After installing the green roof, conduct a flood test. This consists of flooding the roof with 1 inch of water that sits from 24 to 48 hours. If no leaks ensue, the new green roof is a success.

1. Build roof on a small incline of 1/8 inch per foot. Achieve this with a foam underlay. Flat roofs are not truly flat. They typically run on a 1 percent slope, which allows for runoff.
2. Sheathe with plywood: Place plywood sheathing on top of framing with an 1/8" gap at all joints (allows for expansion/contraction).
3. Screw down underlay: Sheet rubber roofing material requires substrate.
4. Beveled corners: Where the roof buttresses the parapet, a rubber roof needs to run up the wall and be glued to sheathing. Beveled corners prevent water from pooling in corners.
5. Before laying down the roof, sweep thoroughly to prevent debris from puncturing the roof.

•Flat roofs work best when using drains or automatic siphons.
•A flat roof should never experience more than 48 hours of standing water.
•Inspect the roof for cracks, leaks, holes or other damage following major storms and on an every six-month basis.
•Ninety percent of all roof leaks begin at flashings.
•Clean drains of all debris every six months.