FLAT ROOF PONDING

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A flat roof comes with a lot of benefits.  But there is one definitive downside to those flat roofs: pooling water.  This is because flat roofs do not drain water as effectively as their pitched counterparts.  Those pitched roofs have a natural slope where the water can run down, draining off the roof.  Because these roofs don’t drain water that well, they are prone to developing what is known as ponding water.  Ponding water is known in the roofing community as water that stands in a puddle on the roof for more than 48 hours at a time.  Ponding water might not be an immediate threat, but if it is allowed to persist over time, that water can begin to wear on the roofing membrane.  This leads to a decline in the membrane’s lifespan and can lead to things like leaks which can cause serious problems for the rest of the building.

Water ponding is when water builds up and stagnates on the surface of a roof for longer than 48 hours.  Large puddles can form on the roof surface because the drainage system is not adequate for the structure, or due to a variety of other issues with the roof design or the building infrastructure.  Because there is a high volume of liquid, it cannot evaporate off the roof and the stagnant water has nowhere to drain.  Standing water on a flat roof for 12-36 hours after a rainstorm can be normal, but any water found ponding on flat roofs for longer than 2 full days should be examined by a professional commercial roofing contractor.

The forces of gravity make significant water buildup on flat roofs a problem because the only place water can eventually go is down.  Ponding water poses a significant risk to the flat roof system over time and must be fixed in order to protect the structural integrity of the entire building.  Thankfully, there are a few different tactics that you can employ to resolve those ponding water issues on your flat roof.  It is important that you address this issue because of the aforementioned leak potential.

How To Stop Water Pooling On A Flat Roof?

Despite the advantages of having a flat roof, there is one major downside.  Flat roofing does have a small slope, but this does not allow for proper water drainage, in the same way as pitched roofing.  Not being able to drain water means there is a risk for pooling, which means that water can collect and puddle.  Pooling water might not be an immediate threat, but if it is allowed to persist over time, the risk of serious problems increases.  Puddles of water are heavy and can begin to wear away at roofing materials, reducing the roof’s lifespan. A weakened roof system can lead to things like leaks which can allow water to easily access the rest of the building.

Thankfully, there are a few tactics that your professional roofer can employ to take care of pooling water, but it is important to take care of this right away.

Flush Existing Drains

Drains collect debris over time and can become clogged, leaving water nowhere to go.  This leads to pools on the roof.  To prevent that buildup of debris, make sure you remove sticks, leaves, and all other debris from the roof often.  Debris becomes a real nuisance when it collects, so it is best to clean out the drain often.  Whether you clean the drains yourself or hire a professional roofing service, drains should be cleared out at least twice a year.

Like the drains that live in your home, drains on flat roofs can eventually become clogged with debris.  In more extreme cases, these serious clogs can actually lead to standing water becoming a mainstay on your roof.  To prevent that buildup of debris, try removing sticks, leaves, and any other rooftop debris from the drainage system of your building.  Not only will this allow rain and melting snow to flow away from your building, but it will also prolong the life of your drainage system as well.

On its own, that debris seems harmless.  But when it builds and builds, it can lead to various issues with not only your roof but the drainage system as well.  Take those preventative measures, and you should not only see a longer life for your drainage system but your roof as well.  You can also hire a professional roofing service to come out and perform those preventative cleanings on your drainage systems once or twice per year. That should be adequate to keep your drainage system clean and working optimally.

That bit of preventative maintenance might cost a little money in the short term but will save you a lot of time, money, and trouble in the long term.

Replace The Membrane

The roof membrane protects your roof from moisture and other elements.  Pooling water can damage this membrane, which prevents it from protecting the building.  Moisture can build up and seep into the building structure, causing serious structural damage.  Pooling water is one of the most common reasons for a damaged membrane.  Most roofing membranes are designed to withstand water ponds, but you need to take care of the membrane in order for it to do this job properly.  Invest in one of the more effective, modern versions and with regular preventative maintenance, your membrane will be stronger and last.  Membrane maintenance includes having a roofing contractor inspect the roof once or twice per year.

Fix Low Spots

Since flat roofing is not entirely flat, there are subtle slopes that develop as part of the installation process.  The small slopes are designed to facilitate proper drainage, but weak spots can develop as with all slopes.  These are perfect for debris and water to collect. Low spots become an issue and pooling can occur quite easily.  When this happens, the drains can become clogged with debris which forces water to pool at the roof surface.  The membrane can become damaged and leaks can develop.  A professional roofing contractor can identify these low areas and take care of them.  You can also add more drain lines to the building to help prevent pooling at low spots.

Despite the fact that they are called flat roofs, commercial flat roofs aren’t always completely flat.  This is because there are subtle slopes on the surface of the roof that can come as a result of the installation process, weak spots in the roof, or a particular focus of debris or precipitation.  Additionally, qualified contractors understand how to slope a flat roof for drainage.  These slopes are meant to facilitate drainage so that there is not a lot of pooling water on your roof.  It helps to remove that extra water off to the edges of the building, where an external drainage system lives, or to designated internal drains that will carry the water away.

One of the flaws of these low spots is that water ponding can occur quite easily.  When that happens, the drains can clog with debris and fail to do their job.  This leads to a buildup of water that can cause damage to the membrane of the roof and eventually cause leakage.

Re-pitch The Rooftop

Pitch that was not properly designed or installed can also lead to pooling water.  If there is not enough pitch, water cannot drain as needed, leading to water pooling.  Re-pitching can be an expensive investment, but in many cases, it is the only solution. Especially, if you consistently have issues with pooling.

Install Roof Crickets

If you see that water is collecting more easily in certain areas, you may want to use roof crickets.  Water often collects easily at vents and chimneys, and roof crickets can help reduce this.  Crickets are rigid structures specially designed to divert water around obstructions such as vents and chimneys.  When the roof has trouble naturally draining water on its own, roof crickets can help.

When it comes to pooling on your flat roof, you might find that the water ponds in specific areas.  These areas typically are near chimneys or around large vents.  The best way to battle water ponding in these areas is to install roof crickets in those areas.  Crickets are ridged structures that have been designed to divert melted snow and rainwater around roofing obstructions like the aforementioned chimneys and vents.  Because of their positioning or design, those obstructions may have a naturally difficult time draining water on their own.

Adding crickets to these obstructed areas can also help when standing water is typically associated with transitions between roof areas.    If you are experiencing ponding water in other areas of the roof, crickets might not be enough. It is important to know how to drain water from a flat roof. 

Add More Drain Lines

If the current drainage system has issues with effectively removing water from your flat roof, there are a few things that you can look into in order to help the process along. Though it comes with additional costs, adding additional drains is one of the most effective ways to take care of this issue.  Flat roofs, particularly those in areas with high precipitation, will sometimes need those additional drains to properly clear the water from the roof.  Unfortunately, most building owners don’t realize this until they see that water ponding becomes a substantial problem in the wake of a heavy storm.

Most professional roofing contractors worth their salt can install extra drain lines or even widen the existing drains attached to your building in order to direct that excess water away from the rooftop.  Again, this is an extra cost, and most building owners will avoid this option.  Still, it isn’t out there if there is a more efficient option than this.

Compress Insulation

Another problem that can lead to pooling water is compressed insulation.  Compressed insulation is generally caused by heavy roofing equipment and repeated treading over the roof area that can lead to indentations in your roof.  These dents are perfect for collecting water, so you need to ensure that the proper precautions are taken with the insulation and during any inspection processes.

One of the most important aspects of building ownership is maintenance.  And this includes the roof.  Preventative maintenance is the best way to address pooling water and damage, so your roof can continue to work efficiently.  Flat roofing is known to develop pooling water easily, so being prepared and maintaining your roof is the only way to prevent it from becoming a serious issue.

Vegetation growth

The longer water builds up on a surface, the more likely you are to experience vegetation growth.  Moss, algae, and other plants can do long term damage because they turn the roof’s surface into it’s own ecosystem.  The plant’s roots dig into the roof materials and if gone untreated for a long period, can begin burrowing into the insulation and substrate underneath, which could be made of wood, steel, or concrete.

If you have plant growth, the roots could be bringing moisture into the structure.  It’s best to get out in front of this problem before it can cause unnecessary damage.  Many building owners learn this hard way, when the cost of roof repair turns into a cost for both repairs and potentially mold and mildew removal. 

Dips near roof features

Certain roof features, such as skylights or plumbing vents, may have been installed with small dips that allow for ponding and become worse over time.  It is essential to get an experienced roofing professional to install these features and their flashing to prevent this problem.

HVAC leaks

Sometimes HVAC equipment that is installed on the top of the roof causes ponding because it is too heavy and creates a dip in the roof.  The ponding water may also be normal condensation or an abnormal leak from the air conditioner itself.  The water may be slowly draining but resupplied by the machinery.  In this case, you will need an HVAC professional to fix the equipment’s leak or reroute the normal condensation.

Sagging roof deck and potential collapse

Roof collapses are the worst case scenario for any property owner.  Besides the need for tenets and/or businesses to evacuate, there’s a serious risk of property damage and in extreme cases, the loss of human life.  But what does this have to do with long-term water accumulation?  When water begins ponding on a roof, the areas underneath start to deteriorate. Because the roof materials themselves are not completely waterproof like a swimming pool liner would be, they start to break down over time.  Water saturation increases, leading to more weight for the structure to hold.  Rotting materials and extra weight are not a good mix! And this is exactly where the risk of a cave-in is heightened.

Frequent roof leaks

Water ponding increases the likelihood of leaks because it deteriorates roof materials, as we discussed above.  Once you start seeing a roof leak on the interior of the home or building, the issue is much greater than one small leak.  So, if you have a roof leak issue under ponding water, it may not be a simple repair and we recommend contacting an expert to do so.