Roofing

ROOFING

A roof that is nearly flat or slightly pitched is called a flat roof or low slope roof. No roof should be dead flat because it must have at least a slight slope to drain.

The terms low-slope and steep-slope describe roof slope. Slope is how much a roof slants. A low-slope roof is one that has a slope of less than 3-in-12. This means that for every horizontal foot, the roof level goes up less than 3 inches vertically.

A steep-slope roof (typically a shingle roof) depends upon gravity to cause water to flow in one general direction so it can shed the water over the breaks and fasteners in the shingles until it flows to the edge. A low-sloped roof or flat roof, cant depend upon the water to flow in any particular direction so it must form a watertight, monolithic membrane that stays watertight all the way to the drains or edge.

Modern low-slope roof or flat roofs tend to use a continuous membrane covering which can better resist pools of standing water. These membranes are applied as continuous sheets that are bonded together with heat-welding or adhesives. Far more expensive low-slope or flat roof options (mostly for smaller traditional residential applications) include sealed metal roofs using copper or tin. These are soldered interlocking systems of metal panels.

Traditionally low-slope or flat roofs would use a built-up (tar and gravel) roof, which used to be good enough. Today, this traditional type of roofing suffers from performance, cost, and environmental issues that require other solutions to be considered a better value.

So besides having to stand up to wind, freeze-thaw cycles, and UV radiation from the sun like shingles must, a low-slope system must also withstand expansion and contraction of the building and all of the other dynamics going on above a building while staying 100% watertight. This requires well-engineered attachment, seaming, and weathering characteristics to meet these performance demands.