How to Fix Ponding on a Flat Roof

Flat roofs, by their very nature, will collect some water when it rains. However, excessive ponding threatens your roof. It may also void your warranty. So if your flat roof is collecting water that doesn’t drain or evaporate within 48 hours, you will need to fix it. How to fix ponding on a flat roof depends on the cause of the ponding. The issue may have to do with the slope of the roof or with its drainage. Whatever the cause, you can’t let it be, or you risk serious damage to your roof. So if you have a flat roof that isn’t draining, you will need to contact a roofing expert like Eagle Watch Roofing as soon as possible to get it fixed.

Ignoring Ponding Water on a Flat Roof

Does your roof have issues with ponding water? Every flat roof will collect some water during periods of heavy precipitation. If you have some water on your roof after a heavy rain, for instance, but the water is gone in a couple of days, your roof is doing just fine. The problem is when the water sticks around. If you still have water of an inch or more after 48 hours of dry weather, you have water ponding that requires attention.

What happens if you just ignore the ponding?

The most obvious problem with ignoring ponding water is that it can lead to leaks. Water always looks for the lowest place it can go, If water is properly draining from your roof, it will quickly find the lowest spot on your roof, which should be a gutter or drain. From there, the water will be directed off your roof. But if the water is pooling, the pooled water is looking for the lowest place it can go. If there are any cracks or opening in your roof, the water will find its way through those cracks and right through your ceiling. And if there weren’t any cracks before the water sat around in a big puddle, the water itself can weaken the structure of the roof and create cracks and holes.

Another problem with leaving pooled water on your roof is the ability of water to act as a magnifying glass. Besides water, one of the main damaging forces your roof has to stand up to is ultraviolet rays from the sun. Your flat roof is built to withstand regular ultraviolet rays for many years. However, when those rays are concentrated and magnified by a pool of water, their effects are much worse. Again, this can cause deterioration of the roof surface. If water pools in the deteriorated area it can find its way through the roof and cause a leak.

Another side effect of pooling water is that the water collects dirt from the entire surface of the root and as it slowly evaporates it leaves behind a pile of mud and dirt. If left untreated, the dirt can actually grow vegetation. And this is no “green roof”. Instead, the vegetation will slowly break apart your roof as its root system gets into the material of your roof.

First Step: Fixing The Drainage

If water is pooling on your roof, the first place to look is at the drainage system. If you’re lucky, the drainage will be the problem, since that’s the easiest thing to fix. Start by looking for plugged drains. Often, something as simple as a clogged drain can cause serious pooling on a flat roof. Unclogging the drain will solve the problem.

The next place to look is at gutters or draining channels. Just like a drain, when a gutter or drainage channel is stopped up, water can’t flow and will inevitably collect on your roof. If that’s the only problem with the roof, it can be easily fixed. You’re in good shape.

But what if it looks like the drains and gutters are working correctly, but there is still water on the roof? There is still one more drainage solution. It is possible to create a new drainage channel to drain the part of the roof that is collecting water. This should only be done by an experienced roofer.

Fixing a Low Spot

If the drainage seems not to be the issue, you have another option. Water will always flow to the lowest spot, so if water is pooling in a certain area, that means that it is lower than the surrounding area. Every flat roof is actually slightly pitched. The slope of the roof is just enough to direct water into the drain or gutters. But if another part of your roof is indented or has a low spot, the water will collect there before it can reach the drain.

There are a few options for fixing a low spot. A professional roofer can usually fix a low spot in a roof with some roofing plaster. The roofer will fill in the low area and give it a slope to match the existing slope of the roof.

Fill a Low Spot Yourself

If you prefer a DIY approach and are somewhat handy, you can try filling the spot yourself. One way is to use layers of rolled asphalt roofing. The basic theory is that you will build up layers of rolled asphalt roofing to fill in the depression.

To do this, you first need to make sure that the puddle is completely dry. Use rags or towels to remove any moisture. Start by cutting out a 12-inch circle of asphalt roofing Apply a thin layer of roofing cement to the bottom of the asphalt roofing, making sure to get it all the way to the edges. Place the asphalt roofing at the center of the depression and press it firmly into place. Next, cut out a 16-inch circle of asphalt roofing and install it the same way. Cut more circles, each time adding 4 inches. Place a 20-inch circle, a 24-inch circle, etc. Install 10 layers in all.

After the asphalt roofing layers, cut two pieces of nylon larger than the last circles. Apply each layer of nylon with roofing cement, one on top of the other. Finish it off by painting the whole area with a thick layer of rubberized or elastomeric coating Extending several feet beyond the patch in every direction.

Fix the Slope of the Roof

If the roof isn’t draining right and it looks like there is more than just a single depression in the roof, your problem may be more serious. It’s possible that the roof just wasn’t built with the right pitch. In theory, a slope of 1%, or 1/8-inch per foot, is enough to drain water. However, building codes usually require twice that, a 2% slope, or 1/4-inch per foot. That would mean that a roof that is 20 feet long would be 5 inches lower on the drainage side. If the roof wasn’t built to code, you will need to rebuild the roof. This can be an expensive option, but it may be the only solution.

One interesting new technology for adding slope to a roof that doesn’t have sufficient pitch is to use tapered insulation. These are slope panels of solid insulation, usually 4’ x 4’. Adding tapered insulation will fix the slope of the roof and add to the building’s energy efficiency. It is not cheap, but if you have to fix the slope, this option has the extra benefit of added insulation.

If your flat roof has ponding water, let the experts at Eagle Watch Roofing take a look. We’ll come up with the best solution to keep your roof and the structure below in good shape. Contact us to learn more.