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A flat roof doesn’t divert water as quickly as a sloped surface. However, flat roofs should drain or evaporate completely within 24 to 48 hours after a rainfall. If water pools on the roof for longer than that, it can damage the structure and pose a safety risk.

What Causes Flat Roof Ponding?

Understanding what causes water to collect on a flat roof can help you determine how to fix it. Some of the most common causes of ponding on this type of surface include:

  • Poor drainage – Inadequate or clogged roof drains prevent water from leaving some roof areas.
  • Depressions near roof features – Skylights, plumbing vents, chimneys and other roof additions may be bordered by dips that collect water.
  • Sunken spots – The settling of older buildings or existing structural damage may cause some areas to sink lower than the rest of the roof. Drooping insulation and rotting joists are often to blame.
  • Incorrect roof pitch – Flat roofs slope slightly, allowing them to direct water to the drainage areas. A roof without a sufficient pitch can contribute to your ponding problems.
  • HVAC leaks – Malfunctioning or heavy HVAC equipment that’s installed on a flat roof can create pooling.

How to Fix Flat Roof Ponding

If you discover ponding on your flat roof, it’s best to have a professional inspect the area. A roofing expert will be able to identify the source of the problem so that you can take appropriate measures to correct it.

Correct Drainage Problems

Although you may fear the worst, you might be surprised to hear that your roof simply needs a good cleaning. When dirt and debris gather in drains, gutters and drainage channels, they block the flow of water. Regular roof maintenance can improve water flow and prevent blockages from happening.

A licensed roofer can also create new drainage channels to redirect water away from problem areas. If certain drains are frequently clogged, adding a screen can filter out particles that might otherwise obstruct the flow of water.

In the winter, freezing temperatures can cause ice to choke off the roof drains. Professional roofers can suggest options for remedying this situation. You may need to install heated features that prevent ice from building up or revamp your snow removal procedures.

Repair or Replace Roof Features

You may need to repair or replace roof features that are collecting water. Contact a roofing professional that is experienced with flat roofs. They’ll reinstall the feature properly and add adequate flashing to divert water and encourage drainage.

Fix Sunken Areas

There are many products available to fix sunken spots on a flat roof. However, you shouldn’t take on the project yourself without an intensive examination.

If the low spots are caused by structural damage beneath the roof, you may have to call in the professionals to repair the issue. Covering it up without resolving the root of the problem can cause more harm in the long run.

Correct the Roof Pitch

If your building was not built to code, the roof may not be pitched correctly. Rebuilding the roof may be your only option. If that’s the case, you need to work with professionals who are familiar with flat roof installation. Using advanced materials, such as thermoplastic polyolefin or ethylene propylene diene monomer, extends the life of your roof and reduces the risk of pooling and moisture damage.

Address the Insulation

Heavy HVAC equipment can cause your roof to sink because it compresses the insulation beneath it. Lots of foot traffic on the roof also packs down the insulation and creates dips. The weight of the water that collects in a puddle can even tamp down the insulation over time, creating bigger problems.

A professional can ensure that your roof is designed to withstand the equipment that sits on top of it. We can upfit a roof for this purpose and correct insulation issues that are caused by compression and moisture damage.

When to Fix Pooling on a Flat Roof

Short periods of pooling aren’t normally a concern. However, puddles that stick around for days can cause cumulative damage. That’s why it’s so important to fix ponding as soon as possible.

Water that continues to accumulate on a flat roof eventually causes the following types of damage:
• Vegetation growth on the roof, which damages the structure and poses a slipping hazard for people treading on the surface
• Infestations of pests that are attracted to moisture
• Premature deterioration of roofing elements
• Mold and mildew problems indoors
• Weakening and rotting of structural materials
• More severe sagging

Regular maintenance can prevent your roof from developing the issues that contribute to pooling. Because you should limit the amount of foot traffic on a flat roof, it’s a good idea to hire a professional to perform this task. Roofing technicians know where to walk to avoid damaging the structure.

If a pooling problem has already developed, contact Presidio Roofing right away. We will take a look at your roof and offer solutions, including a free estimate.