FS Roof System Blog

Ponding Water on the Roof Leads to Roof Damage

If you own, or manage, a building with a flat roof, you may have noticed an issue with ponding water. Some flat roofs, due to their design or installation cannot properly drain the water created by heavy rains and snow melts. Leaving you with standing water, generally in the center of your flat roof. While this may not seem like a huge issue, the problems that ponding water can cause can be very costly.

Ponding water can cause many long, and short-term effects. So, here a few things that you should know to protect the large investment that is your flat roof.


Ponding is an area of standing water that develops after heavy rains, or snow melts. It is classified as water that does not properly drain within 48 hours. Chances are this water will remain much longer than two days though. This can cause many long-term effects, and in the worst case may result in the need for a full flat roof replacement. Best case, a costly repair.

There a few different reasons as to why this water may not be draining as it should:

  • If your drains or gutters have not been cleared recently, there may be a blockage of debris preventing the water from draining.
  • The pitch of the flat roof may not have been constructed correctly.
  • If there is too much roofing material towards the edges of the flat roof, it may be blocking an avenue for the water to drain.
  • The flashings themselves may not have been installed properly.

What kind of damage can be caused by ponding water?

Though a little water on your rooftop may not seem like a cause for alarm, if left alone it can cause serious and costly damage to your flat roof.

  • Ponding water can magnify UV rays, speeding up the damage caused.
  • Due to the weight of the ponding water, your flat roof can experience a sag. This will seriously undermine its integrity.
  • Algae and moss growth are common issues that are found in areas where ponding is prevalent.
  • Due to the deterioration that is caused by the algae growth, magnified UV rays, and the weakening of the roof membrane, leaks can become an issue.
  • As your roofing membrane is weakened, and leaks begin, the structural integrity of your flat roof may become compromised. This results in many risks, including a full or partial collapse.

So, you’ve noticed ponding water, and know you know the risks. What are your options for rectifying the issue to ensure no further damage is caused?

The most obvious, yet often overlooked solution is to have your flat roof regularly inspected, and maintained. This will ensure that any issues that you may have with standing water will be found quickly, and rectified efficiently. The best times to have your roof checked, are in the spring, and prior to the winter. If you know that you have an issue with ponding water, you may benefit from having an additional inspection done after a period of heavy rainfall. This would also be a good time to ensure that your gutters and drains are clear of any debris.

The first place that you should check should you notice an area of ponding water is the drains. If these are blocked, that is likely your problem. Clean them thoroughly, and see if the water is able to drain. If this does not help, you might have a pitch issue. There are also solutions if pitch is the problem, though they are a little more in depth, and will likely require a professional.

  •  Widening your existing drains may help the water to drain more thoroughly.
  • By adding more drains, you are inserting more avenues for the water to properly drain.
  • Adding a slight slope to your flat roof will help to direct the standing water towards the drains.

If your issue with ponding water is ongoing, speak with an experienced roofing professional about your options, and the benefits of a flat roof maintenance plan.