When to Worry (and What to Do) About Ponding Water

March 28, 2022

Just because it’s common, doesn’t mean it should be ignored. We’re talking about ponding water on your roof. Some puddles after the rain passes are normal, but if water is still present 48-72 hours later, consider taking action.

Why is ponding water on the roof a problem?

Water that sits on the roof for extended periods of time reacts with the membrane and causes premature aging (i.e. the water acts like a magnifying glass, intensifying damage from the sun’s ultraviolet rays), thereby shortening your roof’s life.

Additionally, the water attracts environmental debris like dirt and sprouting seeds that may result in clogged drains or roof membrane damage. It can even enable algae and microbial growth, not to mention being a slip and fall hazard for anyone accessing mechanical equipment on the roof.

If enough water accumulates, it’s a structural load concern. Even if roof collapse isn’t the result, protruding fasteners may be. Ponding water also increases the odds of severe leaks.

Why is There Ponding Water on my Roof?

There are four primary causes of ponding water on the roof: poor roof design, impeded drainage, lack of roof maintenance, and deflection.

No. 1 Poor Roof Design

Slope is what pushes water to roof drains; without it, you’ve got standing water. Building codes provide requirements for how much slope is necessary. For instance, the International Building Code (Section 1507 Requirements for Roof Coverings) specifies that thermoset and thermoplastic single-ply, built-up, modified bitumen, liquid applied, and sprayed polyurethane foam roof systems have a design slope of not less than one-fourth unit vertical in 12 units horizontal (e.g. 2-percent slope) for drainage. Likewise, roofs that have inadequate or poorly designed drainage systems, will often suffer from ponding water. The proper number (and placement) of roof drains, as well as secondary drainage is critical.

No. 2 Impeded Drainage

Modifications to the roof, such as the addition of a smoke hatch or skylight, can impede drainage if their placement blocks the path of water flow. It’s important to take careful consideration when making roof modifications so curbs don’t obstruct drainage.

No. 3 Lack of maintenance

Regular, routine maintenance will ensure that drains and gutters are not clogged. Without roof drainage systems working the way they were intended, rainwater is trapped without a path to escape. It pools on the roof and, if perimeter edge drainage cannot alleviate the water, the roof fills up like a bathtub. As the water level on the roof rises higher than flashings and pitch pockets, leaks are probable.

No. 4 Deflection

A depression in the roof provides an opportune place for water to collect. Deflection, caused by a corroded deck, wet insulation, or heavy rooftop equipment may be to blame for those large puddles.

What Can I Do to Fix Ponding Water on my Roof?

A professional roofing contractor can help you identify the source of the problem and prescribe a practical solution. They may suggest improving the roof’s design by pouring tapered lightweight concrete or using tapered insulation if the deck doesn’t have adequate slope. Crickets can also remedy low points and saddles installed on the high side of curbs will keep rainwater or melted snow moving toward drains. Adding drains or sump pans can make a big difference too, along with lowering and enlarging gutters.

It’s important to routinely schedule and perform general preventive roof maintenance. Routine inspections and regular cleaning will ensure drainage paths are clear, as well as identify roof design inadequacies or the early signs of damage from ponding water.

Contact D. C. Taylor Co. at 319.731.4118 to evaluate and remedy your ponding water problems.

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