How ponding water affects commercial roofs and what to do about it

Commercial roofing systems are prone to all sorts of issues that arise from weather incidences that are often really hard to see with the naked eye. While low-slope roofs, often associated with commercial properties, are constructed to withstand abuse from the elements, they have one particular downside – they’re often out of sight. 

Ponding water on commercial roofs is considered to be one of the most common threats to roof durability and is attributed to a large number of emergency service calls resulting in flat roof repair. While every occurrence of ponding water is not a telltale sign of damage to come, it should be monitored and addressed as soon as possible. This blog post should inform you of the main aspects to be aware of regarding ponding water on flat roof systems. 

What Does Ponding Water Mean?

Ponding water, often called ‘incidental ponding water’, means that water from events like rainfall has accumulated in puddles on a flat roof system and has not drained away from the building via a drainage system. To a certain extent, every flat roof system is intended to withstand a reasonable amount of ponding water until it eventually evaporates away, leaving the low-slope roof nice and dry. A period of 48 hours of ponding water is considered to be a typical safe duration for lingering pools of rainfall. 

Pools of water are most common in valleys on the roof, a place where two pitches come together, and when the precipitation is excessive it can lead to a large amount filling up quickly and therefore not drying in a desirable amount of time. It’s worth mentioning that ‘flat’ roof systems on commercial roofs still have a degree of slope to them to better allow for positive roof drainage. 

Ideally, the water from rainfall, or a leftover pond from a fastidious roof cleaning, is able to flow to a drainage point that is strategically placed on the roof, naturally leaving the surface dry after a few hours. When objects block these areas, ponding water on flat roofs is bound to appear.

Drains and other water-shedding mechanisms can become obstructed by leaves and other debris that clog gutters and cause ponds of rainwater to appear. Unfortunately, these instances can lead to troublesome damage for a flat roof system. 

It is incredibly important for property owners and managers to be aware of when and where ponding water occurs on the roof and they should quickly develop a plan to clear off any excess pools before expensive roof damage such as leaks and mold occur.

Does Ponding Water Damage A Roof?

Ultimately ponding water on flat roofs that are not dealt with properly will lead to damage like leaks and mold, requiring flat roof repair. When water is left on flat roof surfaces for too long it begins to saturate the roof membrane, breaking it down and rotting it away over time. Once this process begins, a major roof repair is needed and the results will most likely be costly. 

Once water has begun to pool on a flat roof it will start to grow mildew, moss, and other organic matter – think of a pool of stagnant water that begins to turn green and brown. 

These ponds of water can seriously degrade and deteriorate the roof membrane and cause the decking and insulation to become saturated, spelling even more worries for the building manager. Wood rot and decay should be avoided at all costs by those hoping to maintain a sound commercial roof structure. 

Remedies For Ponding Water On Flat Roofs

What can be done to prevent or fix ponding water on flat roofs? There are several ways to approach caring for low-slope roofs, and the first line of defense comes from something stated earlier – getting a professional set of eyes on the roof. 

Since commercial roofing is often out of sight for most people on the ground, there is far less chance of anyone seeing problems beginning to develop. Schedule an appointment with a trusted commercial roofing company to safely and securely inspect the roof, and to receive expert advice on actions to take. 

If more than a simple cleaning of gutters and scuppers is necessary to improve roof drainage, they will most likely suggest some of the following solutions when ponding water is prevalent on your flat roof system. 

Consider A Partial Or Full Roof Replacement

Ponding water can be created from wet or damaged insulation, so removing and replacing these areas can help drastically. When replacing roof components under the surface membrane, a replacement is often necessary. In some instances, you may also get the benefit of choosing a more suitable roof design that sheds water better. This is one of the most straightforward solutions for flat roof repair.

Consider A Tapered Roof System

Tapered insulation has a slight pitch to it, typically 1” over 8’, 1” over 4’, or 1” over 2’. While this sounds small, it makes a big difference on completely flat roofs that hold water. The downside of tapered insulation is that it is very expensive. Creating a pitch like this on a flat commercial roof system can increase the amount of insulation used dramatically. Additionally, installing a tapered roof system is like installing a puzzle, each piece has a place.  So, installing a tapered roof system can add a substantial amount to the cost.

Add Additional Drains

If interior plumbing can be added easily, installing additional drains is one of the easiest and most cost-effective solutions to ponding water on flat roofs, especially if ponds are concentrated in just a few areas. Essentially a new drain with sumped insulation would be installed making the roof area slightly lower around the drain. With the help of a licensed plumber connecting the drain inside the building, property owners can count on an effective roof drainage system.

Add A Scupper Box

If the ponding water is located near the edge of the building, or if interior plumbing is not an option, building owners could consider a scupper box and downspout. This would involve installing a new scupper box, downspout, and sumped insulation near the edge of the roof. Sumped insulation basically means that the insulation is lower around the scupper box than the surrounding roof, which helps promote drainage. When necessary, a larger relief can be cut into the roof so that water has a path to the downspout.

Trust The Professionals

At Chaffee Industrial Roofing, we are dedicated to giving the best solutions for your roof. Whenever you need flat roof repair or are simply looking for advice, we’re here to help. Don’t invest in your roof without first consulting the team with over 100 years of experience. Call Chaffee today!

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1 Comment.

  1. Now this is a VERY interesting post. Especially this….
    “As a general rule of thumb, most single-ply manufacturers require 80% of water to be off of a roof within 48 hours of a rain event. So, if there are a few places throughout the roof that have some ponding water after this 48-hour point, it is within the design of the roof system”
    Thats a real gem. Thank you for posting this. Seriously good information

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