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Raleigh Commercial Roofs

Serving Raleigh and nearby areas

Ponding Water on a Flat Roof in Raleigh, NC

Water that is still on a flat roof 48 hours after rain stops is called ponding, and it wears the roof out early, so call (984) 464-8602 for a free inspection that finds the cause and prices the fix.

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We connect property owners in Raleigh and nearby areas, including Research Triangle Park, Durham, Cary, Morrisville, Apex and Holly Springs, with one independent local commercial roofing specialist.

  • The 48 hour line

    Roofing industry guidance defines ponding as water that stays on a roof 48 hours or longer after rain. Standing water that dries sooner is treated as normal.

  • Water is heavy

    Each inch of water on a roof weighs about 5.2 pounds per square foot. Two inches across a 1,000 square foot low spot is more than 10,000 pounds.

  • September is the wettest month

    Raleigh averages about 46 inches of rain a year, and September brings the most. That is when slow drains show up.

What it costs

Typical published ranges for Raleigh. The contractor's written estimate is the price, and the inspection is free.

WorkTypical range
Ponding area repair $70 to $750per repair
Drain repair $70 to $500per repair
Membrane patch at a worn ponding spot $250 to $1,750per repair
Seam repair $200 to $1,000per repair

See typical commercial roofing prices in Raleigh

What ponding looks like

Every flat roof holds a little water after a storm. Ponding is different. It is the same puddle in the same place, still there two days later. Here is what managers and maintenance staff notice:

A puddle that never dries

Between storms in spring and summer.

Rings of dirt or algae

On the membrane where water sits and then dries.

A green or dark patch

That shows up in aerial photos or from a taller building.

Water backed up around a drain

With leaves or debris on the grate.

Water against a parapet wall

Or at the base of an AC curb.

A dip you can feel

When you walk the roof, or see from the ceiling below.

Leaks that start in the same spot

A day or two after a storm.

Why water ponds on Raleigh roofs

Clogged drains and scuppers. This is the most common cause and the cheapest to fix. Raleigh is known as the City of Oaks, and leaves, acorns and pine straw land on roofs and wash into drains. A blocked drain can turn a whole section of roof into a shallow pool.

Low spots from the start. Code calls for most new low-slope roofs to slope at least a quarter inch per foot toward drains. Older buildings, additions and reroofs over an old deck may not have that slope. Water collects in the flat areas between drains.

A deck that sags. Steel decks and joists can bend over time, or bend under the weight of rooftop units. A sag holds water, the water adds weight, and the sag deepens. Industry writers describe this cycle as a real risk to the deck if it goes on.

Crushed or wet insulation. Foot traffic around rooftop units and old leaks can crush insulation. The roof surface drops a little, and water finds the dip.

Lots of rain. Raleigh averages about 46 inches a year, and September is the wettest month. A roof that drains slowly is tested often.

Why it matters

Weight. Each inch of water adds about 5.2 pounds per square foot. That is why codes require secondary drains or scuppers on many roofs with parapets. If the main drain clogs, the overflow keeps the water from getting too deep.

Wear. Sun on standing water, dirt left behind when it dries, and algae all wear the surface faster. Seams that sit under water are tested every day.

Leaks. Any small opening under a puddle leaks far more than the same opening on a dry slope.

Warranty. Many membrane warranties limit coverage for damage from standing water. Check yours.

Cosmetic or urgent

Usually fine: a few shallow puddles that are gone within 48 hours, with no leaks below and no sag you can see.

Get it checked soon: water still there after 48 hours, the same spot every time, or a puddle that grows over a season.

Call now: the deck or ceiling below is sagging, water is deep against a wall or over a drain that will not clear, or the overflow scuppers are running. Keep people out from under a sagging area.

What the fix usually is

  1. Clear and repair the drains. Clean the grates and lines, reset or replace damaged drain bowls and strainers. Often this alone solves it.
  2. Fill the low spot. A crew can add tapered insulation or a cricket, a small built-up slope that sends water toward the drain, then cover it with new membrane.
  3. Add a drain. If a large area is far from any drain, a new drain or scupper may be the answer.
  4. Fix the deck. Where the deck has sagged, a structural check comes first. Repair or added support may be needed.
  5. Plan for the reroof. Tapered insulation over the whole roof is often done during replacement. If your roof is near the end of its life, it may make sense to fix drainage then.

North Carolina code lets most reroofs of existing low-slope roofs skip the quarter inch slope and secondary drain rules when the roof already drains. If yours does not, ask the contractor how the new roof will get water off.

Before the inspection

  • Take photos of the puddles with the date, one day and two days after rain
  • Note how deep the water is with a ruler, if you can reach it safely
  • Look for leaves or trash on the drain grates from a safe spot
  • Note any rooftop units added since the roof was built
  • Keep service techs from piling equipment in low spots

About these prices

The cost table shows typical repair ranges from Fixr's published flat roof repair guide. They are not quotes. Larger drainage fixes depend on the size of the area and are priced on site.

Call (984) 464-8602 or send the form with the address. A local commercial roofer is set up the same day you call.

Frequently asked questions

How long can water sit on a flat roof?

Roofing industry guidance treats water that is gone within 48 hours of the last rain as normal. Water still there after 48 hours is called ponding and should be checked.

Is ponding water dangerous?

It can be. Each inch of water adds about 5.2 pounds to every square foot. A thin deck can bend under that weight, which makes the low spot deeper and lets it hold even more water. Most of the time the bigger risk is a leak and a shorter roof life.

Will my roof warranty cover damage from ponding?

Many membrane warranties limit or exclude damage from standing water. Read yours, or ask the inspector to check it. That is one more reason to fix drainage problems early.

Can I just sweep or pump the water off?

Pushing water to a drain can help in the short term, but stay off a wet roof unless you have safe access. It does not fix the cause. The low spot will fill again next storm.

Does a coating stop ponding?

No coating removes the low spot. Some silicone coatings are made to handle standing water better than others. The lasting fix is to make the water drain.

How much does it cost to fix ponding?

Published national guides put most ponding repairs at about $70 to $750, and drain repairs at about $70 to $500. Adding tapered insulation or crickets over a large area costs more and is often done during a reroof.

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