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Low Spots on Flat Commercial Roofs

Low Spots on Flat Commercial Roofs

Most commercial buildings have flat roofs as they offer many advantages over sloped roofs. Unfortunately, flat roofs share a common problem known as ponding water. This condition, which is also called “standing water,” occurs when rainwater fails to evaporate off a roof after 48 hours, following rainfall. If you have a flat commercial roof, here’s what you need to know about low spots and how this problem can be prevented and corrected.

Problems That Can Occur from Ignoring Ponding Water

Ponding water causes more damage to flat roofs than any other type of roofing condition. That’s why it’s critical that you don’t ignore this problem. Although it may not be a major issue at first, ponding water can eventually damage your building, leading to expensive repairs, besides other problems.

For example, damaging leaks are a huge concern. What’s more, the performance of a roofing membrane can be compromised. As a result, the lifespan of the roofing membrane is shortened.

Common Causes of Low Spots on Flat Commercial Roofs

There are several causes for low spots on flat commercial roofs. These include:

  • Crushed insulation—Consider how insulation that’s wet and saturated or becomes crushed from a lot of foot traffic can lead to it being compressed. This causes indentations on a roof where rainwater can accumulate.
  • Unprotected skylights or roof top units (RTU) that don’t have crickets can also provide spots where water collects and doesn’t evaporate. Crickets, which are also called “saddles”, are ridge structures that are used for diverting water off a roof.
  • Structural issues in a building can result in low spots on a roof. To determine the degree of structural problems, it’s best to consult a highly qualified and experienced roofing contractor.
  • Inadequate or blocked drainage is another cause. Therefore, a flat roof must have gutters that work properly so that water can drain correctly off a roof.
  • The earth shifting from undergoing freeze/thaw cycles can also lead to low spots on a flat roof.

Identifying Low Spots

It’s important to identify any low spots on your roof. This includes looking for puddles that have dried up. In other words, inspect your flat roof for any dried water marks as this can indicate low spots.

Look for obstructions on drains, examining downspouts and scuppers. When drains are clogged, it’s easy for ponding water to develop on a roof. When ignored, this can cause a roof to sag and weaken, which will lead to leaks.

If these methods don’t show any signs of low areas, then try hosing down your roof so that you can see if water ponds in any areas. Run the water for about 10 minutes in a spot to see if there’s ponding. Then, slowly run water over areas that appear to be low spots. It’s best to have a professional roofer do this job as it can be extremely dangerous.

How Low Spots Can Be Prevented and Fixed

Installing the right roofing membrane is one way to prevent low spots. If your flat roof doesn’t have adequate drainage, you could fix the problem by adding roof drains. Using tapered roof insulation is another solution. This material is designed to direct standing water to drain through internal drains or gutters.

However, the best method for correcting low spots on a flat commercial roof is by using our unique roofing compound product that fills in low spots. RoofSlope is a material that’s both water-proof and durable. This polymer-rich cement substance is made to create a supporting slope over different types of roofing membranes and is designed to direct water to flow to drains, besides scuppers and off roof edges.

Before installing our product, we ensure that the assembly can support the weight of the material as well as inspect all areas needing to be coated. Cure times depend on factors such as product thickness and temperature. Most installations that are done in warm weather and involve a ¾” thickness, or less, are typically fully cured within 24 hours.


Don’t let low spots ruin your flat commercial roof. Please contact us and learn more about how we can fix this problem.


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