commercial-sloped-roofFlat roofing is thought to be completely flat, but a slope is beneficial to these roofing systems, even if it is only small. Roofing needs slopes to prevent the accumulation of water on the surface. Ponding, or the accumulation of water, can happen anytime there is rain and without a slope to lead water away, you end up with pools. It has become more accurate to refer to commercial roofing as ‘low-sloping’, rather than flat. The pitch of a roof determines the materials you use as well as what is best in terms of building design. The ability to effectively shed water and prevent ponding is important to the longevity of any roofing system. The slope of a roof determines how well a roof will perform over time and how long it will last because preventing ponding protects the roof for longer.

The Problem with Low Spots

A low spot can cause problems and can threaten the integrity of the roof and building if ignored. There are several factors that contribute to the development of a low spot.

  • Settling of the building
  • Expansion and contraction of the roofing materials
  • Expansion and contraction of the ground beneath the building
  • Compressed or failing roofing insulation
  • Inadequate drainage that allows water to accumulate

Ponding or the collection of water happens in low spots, and the water can sit for days and even weeks. This invites mildew and mold to grow and can damage the roofing membrane the longer the water sits. Water can also penetrate through cracks causing damage to the internal structure of the roof and building. Low spots and ponding cause sagging, leaks, and serious internal and external damage.

Why do Commercial Buildings have Flat Roofs?

If low spots and ponding are common on flat roofing, then many people wonder why it is used. Flat roofing is useful despite this and they have economic value. They easily accommodate HVAC units and other bulky equipment that can take up valuable real estate and these systems are more economical to build because they reduce the overall volume of the building and save on energy costs. It is important to regularly check and maintain flat roofing to avoid low spots and ponding. With regular inspections, you can identify these problems before serious or permanent damage is caused. You also need to maintain the components such as the scuppers, gutters, downspouts, and internal drains to ensure water flow away from the roof is unhindered.


Adding a slope to a flat roof is an effective way to ensure proper drainage and prevent the development of low spots and ponding. Contact us today to discuss the options available for adding a slope, or repairing any low spots.

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