Why Are There Puddles on My Roof?

April 16, 2019

Ponding water on low-slope roofs is a common problem. It’s so common, you may be wondering if it’s really even a problem. Unfortunately, it is and no one facility or roofing system is immune to it.

Why is There Ponding Water? What Causes It?

Insufficient slope. The majority of roofs with ponding water can attribute the problem to lack of roof slope. Without slope to push the water to a drain, rainwater has nowhere to go.

Poor drainage. Drainage problems are the second most common reason water puddles on the roof. When a scupper or drainage system has no crickets or saddles, a curb obstructs the drainage path, drain sump is inadequate, or drains and gutters are clogged, water ponds.

Deck deflection. If inadequate roofing system design or poor drainage aren’t blame, ponding water may result from a previous leak. If it caused the deck to corrode or compressed insulation, this sagging provides an opportune place for water to collect. Another source of this deflection is the weight of rooftop equipment.

Improper repairs. An inexperienced professional may apply a quick fix a problem (like the leak mentioned previously) without understanding that ponding water could result.

Why is Ponding Water a Bad Thing?

Growth of microbes, algae, and plant matter is a concern whenever there’s ponding on the roof. Water that doesn’t drain properly also attracts environmental debris (e.g. sprouting seeds). Plants can’t grow without moisture and their root systems will quickly destroy a roof membrane and the insulation beneath.

Ponding also accelerates deterioration. Manufacturer requirements state that water should not stand on the roof for more than 48 hours because it reacts with the membrane and causes premature aging. It can limit future roof maintenance options too. For example, roofs with poor drainage are not a candidate for coating application. The coating deteriorates faster because of the presence of ponding water.

It’s a safety hazard as well. Ponding water creates slip and fall hazards. When large puddles become thick sheets of ice in winter, rooftop workers risk injury merely traversing the roof.

Too much water compromises structural integrity. Water that doesn’t drain adds weight to the roof that structural members and the roof deck may not have been designed to hold; it could result in roof collapse. Additionally, severe leaks are likely.

How Can I Prevent Ponding Water?

Inspect your roof. Perform visual inspections after storms to ensure drainage has not been obstructed with environmental debris. Call in a licensed roofing contractor for regular annual inspections and schedule routine maintenance. Regular cleaning and repairs will identify potential problems early and ensure proper drainage.

How Can I Correct It?

Improve the roof’s design by pouring tapered lightweight concrete, adding tapered insulation, or installing additional drainage mechanisms (e.g. crickets). While tapered insulation and roof crickets are costly, the upfront cost pays off in the long run.

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