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The water accumulation on a roof can lead to unpleasant and irreversible consequences for the property. If you're wondering what's causing the water to pool on your flat roof and how to drain it, this article is for you.

We'll highlight everything you should know about water pooling, but the main thing to understand is that the methods to fix this problem are not usually straightforward. Keep reading to learn more about water pooling, its causes, and its solution.

What is Water Pooling?

Water pooling is an issue that occurs due to the accumulation of water on a surface for more than 48 hours. This condition usually occurs on flat roofing systems, mostly due to poor drainage systems, low spots, and other issues in the roof design and overall building structure.

The high volume of the ponded water makes it difficult to evaporate, and the standing water doesn't usually have a drain to pass through. Water ponds standing on flat roofing systems for more than two full days should be inspected by a professional roof contractor.

The accumulated water exerts a lot of force on the flat roof, and this can cause problems over time. It's important to fix this issue quickly to preserve the structural integrity of your building.

Causes and Solutions of Water Pools

Now that we know what ponding water means, let us look at the causes and solutions of ponding water. They include the following:

Poor roof design

In most cases, ponding on a flat roof is usually a result of a poor roof design. If the plan for the roofing structure doesn't match the building layout and shape of the roof, the project is doomed, as the building will experience many issues with time. One of the misconceptions is that flat roofs are easier to repair and replace, but that's not always the case.

Getting a structural engineer to inspect the roofing system systematically is advisable to determine the best way to design the new roof to prevent pooling water. The structural engineer will also examine beams and joists beneath the roof as they often sag with time and cause a pitch on the flat roof.

Foundation settling and building age

After many months, years, or even decades, the foundation of the building will settle, and this can alter the roof design based on the way the foundation settles on the land. Sagging is also natural, making it impossible for builders and contractors to plan for. This problem is common in older structures and buildings but can also occur in newer constructions.

Rubber roofs with many layers

Most flat roofs in major cities are made with different layers. The first layers usually feature gravel and tar, while subsequent layers utilize rubber roofing materials. This is the approach that is generally exploited in flat roof construction.

Laying the rubber above the original tar and gravel base is not usually done accurately to get a perfectly level surface, which can affect the existing slope on the roof. The best way to avoid this problem is for the roofing contractor to be extra careful when the rubber is laid to ensure it's done perfectly.

Crushed insulation

There's always a thick layer of insulation below rubber roofing membranes, and this is to keep heat in the building during colder months and cool air inside during hotter months. Most of the energy lost in the building is usually from the roof, so keeping the roof well-insulated is important.

Insulation is usually made of malleable materials, which can be an issue over time. The insulation can sometimes become depressed because of foot traffic or excessive snow on the roof. This causes uneven surfaces on the roof, which is perfect for water accumulation. The water gathers during rainstorms and forms a pond in the recessed regions.

The solution to this problem is to add more insulation below the rubber membrane or completely change the insulation. This approach can be expensive, but it's the best way to avoid further issues the pooled water will cause. The use of tapered insulations can also help in controlling water ponding.

Lack of draining or poorly installed drains

To keep the roof surface dry, especially after storms, it's important for the flat roof to have adequate drainage. Apart from poor roof design, the absence of an effective drainable is also a major reason for water ponding and roof damage on flat roofs. Due to the negative effects of improper draining, local building codes are in place to regulate this issue across the United States.

Here are some of the conditions that must be met for proper drainage on flat roofs:

  • The spacing between drains should not be more than 80 feet apart.
  • The maximum area per drain is 10,000 square feet, with not less than two drains per roof area.
  • Parapet wall scuppers are a good alternative to inboard drainage systems.

Roofs are not designed to hold water, and another way to avoid this problem is the use of positive drainage. This involves building the roof with graded regions to channel water away from areas with water pools. Another approach is to use crickets to prevent water pooling. This is a great approach to keep water away from HVAC units, chimneys, and regions that are tough to drain.

In addition, it's important to clear debris and keep drains clean. This might sound simple, but ignoring the presence of debris in your drains can cause water to pool on your commercial roof. The good thing is that it's easy to clean drains, and you might not need the help of a professional to handle this.

Problems Associated with Water Pools

Water pooling can cause dark stains and many other flat roofing problems including:

Vegetative growth

Leaving water pools on the roof for a long time can lead to vegetative growth. Algae, moss, and other plants can start to grow, thereby causing long-term damage to the roof because of the development of an ecosystem on the roof surface.

With time, the roots of the plant will dig into the roof materials, which can start to go deeper into the insulation and underlying substrate, usually made of concrete, steel, or wood.

Sagging roof deck

This only happens in extreme cases, which every property owner dreads. It can cause property damage and even the evacuation of businesses. In severe instances, it can lead to the loss of life.

This type of issue only happens in extreme cases following the long-term accumulation of water. Basically, water ponding causes regions below the roof to deteriorate, and they start to break down with time.

Frequent roof leaks

Another issue associated with water pools is that it increases the occurrence of leaks through deteriorated roof materials. After you start noticing leaks in your building, the problem could be more than a small leak. Therefore, if you have a water pool on your roof, the best thing to do is to get an expert to fix it immediately.

Is Standing Water a Flat Roof Problem?

The presence of standing water on a flat roof for a long period is a major problem. As mentioned above, if the water doesn't evaporate or drain after 48 hours, it should be dealt with immediately to prevent serious issues that could adversely affect the roof's structural integrity, leading to severe problems down the line.

In addition, it's best to handle these problems immediately when you notice them rather than wait until it becomes an endless battle of repeated roof repairs. Be sure to hire a licensed roofing contractor who is highly experienced and knowledgeable in designing flat roofing systems with positive drainage.

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