Ponding water is specific to flat and low-slope roofs, and while some standing water is normal for the first day or so after rain, water that stands longer than 48 hours indicates a drainage design problem that will progressively shorten the membrane's lifespan.
It depends on duration. Water standing under 48 hours after rain is generally considered normal on a properly designed low-slope roof. Water standing longer indicates a drainage or slope problem, and prolonged ponding accelerates membrane degradation, adds structural weight, and creates conditions for algae growth and membrane punctures.
Properly designed low-slope roofs include a slight built-in slope (often achieved with tapered insulation beneath the membrane) specifically to direct water toward drains or scuppers rather than let it sit. When that slope is inadequate — from poor original design, structural settling, or additional rooftop equipment blocking flow — water pools in low spots instead of draining.
For minor ponding, additional or repositioned drains/scuppers can solve the problem. For more significant slope issues, tapered insulation crickets (built-up wedges that redirect water flow) are added during a reroof. In some cases, a secondary "overflow" drain is required by code specifically as a backup if primary drains clog.
For adding drains or crickets to correct minor ponding; larger slope corrections during a full reroof cost more.
Most roofing professionals use 48 hours as the threshold — some ponding immediately after rain is normal and expected, but water still standing 2+ days later signals a drainage problem worth addressing.
Sometimes — if the issue is genuinely a drainage capacity problem. But if the underlying issue is inadequate slope, additional drains alone may not fully solve it; a contractor assessment will determine which fix actually applies.
Many manufacturer warranties do exclude damage related to ponding water beyond a certain duration, since it's considered a maintenance/design issue rather than a material defect — worth checking your specific warranty terms.
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