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Reviewed by Tom Reilly — Senior Editorial Reviewer — Roofing, Carpentry & General Contracting

What to do now · Roofer

Standing water on a flat roof: what to do right now

If water is still pooling on your flat roof 48 hours after the last rain, you have a ponding problem. Flat roofs are designed with a slight slope to drain, but sagging decking, clogged internal drains, or shifted insulation can create low spots where water sits. Prolonged ponding accelerates membrane deterioration, adds hundreds of pounds of dead load to the structure, and eventually causes leaks. A roofer can identify the cause — whether it's a drainage issue, structural deflection, or membrane failure — and restore proper drainage with tapered insulation, additional drains, or membrane repair.

Is this your problem?

Symptoms to look for

  1. 01

    Visible puddles or standing water on the roof two or more days after rainfall

  2. 02

    Dark stains or algae growth in specific areas of the roof membrane

  3. 03

    Sagging or soft spots when walking on the roof surface

  4. 04

    Water stains or drips appearing on the ceiling below the flat roof section

  5. 05

    Clogged or slow-draining roof drains, scuppers, or internal downspouts

What to do now

Before the roofer arrives

Standing water on a flat roof

Don't do this yourself

What to do until the pro arrives

  1. From a window or a safe vantage point, note where the water sits, how deep, and how many days after rain it stays — two days or more is ponding.
  2. Check the drains and scuppers from the same vantage point: leaves and a tennis ball are the usual blockages, and a clear drain solves many 'ponding' problems.
  3. Inside, look for staining, sagging or a musty smell under the ponded area.
  4. Photograph everything for the roofer; a membrane under standing water ages several times faster.

What a pro does that you can't

A flat-roof specialist clears and re-forms drains, builds tapered insulation or crickets to restore fall, and replaces membrane that has already been damaged by standing water.

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Who to call

Roofer

A flat-roof specialist clears and re-forms drains, builds tapered insulation or crickets to restore fall, and replaces membrane that has already been damaged by standing water.

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FAQ

Frequently asked questions

Who should I call for: Standing water on a flat roof?

Call a licensed roofer. Roofers have the specialized training, tools, and insurance to diagnose standing water on a flat roof safely and stand behind the fix. Most offer free quotes and can visit the same day or the next.

Can I fix this myself?

No — this is licensed work. The guide above says what to do until the roofer arrives; A flat-roof specialist clears and re-forms drains, builds tapered insulation or crickets to restore fall, and replaces membrane that has already been damaged by standing water.

How fast can a pro come out?

Most roofers offer same-day or next-day visits for non-emergency issues. True emergencies (burst pipes, gas smell, no heat in winter) are typically handled within 1–4 hours.

How much does it cost to fix?

Costs vary by severity and your location. Submit a free quote request to get real pricing from local pros in your area.

What are the signs of: Standing water on a flat roof?

Visible puddles or standing water on the roof two or more days after rainfall. Dark stains or algae growth in specific areas of the roof membrane. Sagging or soft spots when walking on the roof surface. Water stains or drips appearing on the ceiling below the flat roof section. Clogged or slow-draining roof drains, scuppers, or internal downspouts.

Who to call

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