The Flat Roof Specialists

flat roof ponding

Causes Of Ponding On A Flat Roof

Roof ponding happens when low points on your flat roof cannot drain ice or rainwater efficiently. Ponding on a commercial flat roof can have serious consequences if not addressed immediately.

Ponding water can cause premature deterioration of the roof membrane. Ponding water can also cause damage to the building structure, insulation, interior ceiling, and walls. Additionally, excessive standing water can lead to structural failure as well as roof collapse or cave-ins.

Ponding most often occurs on commercial flat roofs for the following reasons.


The building settling process is a part of the aging process for most buildings. However, excessive structural settling could lead to serious problems. Settling occurs when the structure’s weight causes it to crush down into its foundation. 

Settling can be especially prevalent in areas where there are soils that expand and contract depending on the moisture content. Such soils help support a building’s weight, but after several years, they may not be able to support the weight they once did. As a result, a building sinks into the ground.

A settled building can often experience sagging and slumping over time. Eventually, the sagging will result in ponding water on your roof.


A roof drainage system helps direct rainwater from the roof’s surface into downspouts. The downspouts take the water away from the roof and your building’s foundation. 

Drains can clog with dirt, debris, or other foreign objects that get onto your roof. Sometimes, the drains may have damage or are missing pieces like grates or flaps that prevent debris from entering the gutter. 

A clogged drainage system allows rainwater or ice to collect in a puddle on your flat roof since it will not be able to drain into the downspouts.

Likewise, the drainage system might be inadequate for the size of the roof and too small to handle the amount of water shedding from the roof. Moreover, if the roof contractors poorly design the drainage system, water can build up and pond on the roof surface. 

Not enough drains can also cause ponding.


The most common cause of ponding on a flat roof is poor design. A properly designed commercial flat roof should have some slope in order for rainwater to flow off without pooling. 

The slope is how much the roof inclines downward from its highest point to its lowest point. A flat roof requires a minimum slope of 1/4 inch per foot toward the drainage system for the rainwater to drain away from the building properly.


When flat roof insulation compresses over time, it causes unevenness in the roof, resulting in pooling water and ice dams. 

Compressed insulation can result from a few different things. First, crushed insulation can be a result of foot traffic. If you have people frequently walking on your roof or working on it, they could compress the insulation without even knowing it.

The second is if heavy equipment is stored on your flat commercial roof. The weight of all that equipment will gradually compress the insulation so much that water will start to pool in low spots on your roof.

Replace crushed insulation immediately to avoid long-term structural damage and prevent leaks.


The underlying causes of ponding on a flat roof are many and vary from case to case. Knowing the causes can help you solve the problem more effectively. However, whatever the cause, prevention of ponding is always the best option to keep your roof at peak efficiency.

Contact us today to learn more about commercial flat roof maintenance and repairs and how we can help you protect your building.

Scroll to Top