Flat roof ponding repair cost: what to ask the seller
Water still on a flat roof 48 hours after rain is ponding. What the fix costs by cause, who can price it before your deadline, and what to ask for.
Updated · By 
Ben Sikes
How much does it cost to fix flat roof ponding?
Fixr's flat roof repair guide puts the average repair for flat roof ponding at $70 to $750, and says the price depends on the cause. Fixr says the low end covers a clogged drain or a broken seal. If the water sits because the roof has sagged, it becomes a structural repair and costs more. Before you set your ask, get a licensed roofer on the roof after a rain to name the cause and put a price in writing.
Key takeaways
- The roofing trade draws the line at 48 hours: water still there two days after a rain is the problem, not a puddle that dries.
- One Bay Area roofer lists drainage or ponding repair at $2,000 to $8,000+, far above Fixr's national range.
- Ask the seller for the fix the roofer names, not for "ponding." A clean drain and a sagged deck are different requests.
What does each fix cost?
| Source | What the figure covers | Cost |
|---|---|---|
| Fixr, national | Fixing ponding (water pooling) | $70 to $750 |
| Fixr, national | Flat roof drain repair | $70 to $500 |
| Fixr, national | Sagging flat roof repair | $800 to $2,500 |
| Fixr, national | Membrane repair | $250 to $1,750 |
| General Roofing, local Bay Area roofer, statewide list | Drain, scupper, or ponding water repair, California | $1,500 to $6,500 |
| General Roofing, local Bay Area roofer | Drainage or ponding water repair, Bay Area | $2,000 to $8,000+ |
Kept prices every line of an inspection report for $79, usually under 4 hours, and marks the ones that need a professional's quote. To price the other lines on your report, try Kept.
Even the Bay Area roofer's statewide list sits well above Fixr's ponding row, so check what roofers near the house charge.
Two cases show how the cause moves the number. If the roofer finds a clogged drain, the job sits in Fixr's drain row. If the roofer finds a sagged section with damaged membrane over it, add Fixr's sag and membrane rows. That is $800 + $250 = $1,050 at the low end, and $2,500 + $1,750 = $4,250 at the high end. Replacing crushed insulation, and any structural engineer's visit, would add to that. A full reroof for bad slope is not in either case, and only the roofer's written bid prices it.
Is ponding on a flat roof normal?
The answer turns on time. In its trade magazine, the National Roofing Contractors Association (NRCA) calls short ponding "unavoidable and considered acceptable." Past 48 hours, it says, ponding "can be detrimental to the roof assembly."
It gets worse with time. The Asphalt Roofing Manufacturers Association warns that ponding "may lead to accelerated erosion and deterioration of the membrane surface that can result in failure of the roof system." It adds that as water collects, "deck deflections can increase, thereby resulting in additional ponding water which could compromise the structural integrity of the deck." Roofing maker IKO says ponding tends to get worse over time and can end in leaks and early roof failure.
If the report also notes a sag, a soft deck, or a ceiling stain under the flat section, treat it as structural or an active leak. Get the roofer out before your deadline, and ask whether a structural engineer should see the deck.
If the roof is EPDM (a rubber membrane), the EPDM Roofing Association says ponded water "will not void a manufacturer's warranty." That answer covers EPDM only, so ask the roofer what the membrane is.
What causes flat roof ponding, and how is it fixed?
A report photo shows water. It doesn't show why. IKO lists the possible causes, and each has its own fix:
- Clogged or slow drain: clean it, add a better drain screen, or add a new drain.
- Ice in the drain in cold climates: an electric cable that melts it.
- Low spots from foot traffic or storage: a cricket (a small raised ridge) to steer water, or puddle filler to bring the low spot back up.
- Rooftop air conditioner: its weight can make a dip, or the water may be its condensation or a leak. That last part is a job for an HVAC technician.
- Roof installed without the proper slope: IKO says this may mean replacing the entire roof, one of the costlier fixes.
- A building that settled, or structural damage: settling can throw off the slope. Structural damage is fixed first, and the roofer may need a structural engineer or architect.
After the cause is fixed, roofers may also replace cap sheet that sat in water or insulation crushed by its weight. That is where a small job grows. For how ponding compares to other roof lines, see the roof findings hub.
Who can price this before my deadline?
A licensed roofer. Ask for a visit after a rain, so they see whether the water drains. Ask them to write down the cause, the scope, and the price. Fixr puts a roof inspection at $75 to $600 in most cases.
For how fast you can get bids, see how to get repair estimates during the inspection period. For what a general inspector checks up there, see roof inspection before buying.
What do I ask the seller for?
Ask for the repair the roofer named, or a credit equal to the roofer's written bid. Write the scope, the trade, and the source of the number. For example: correct ponding at the rear flat roof as scoped in the licensed roofer's written bid, including any damaged insulation found. Attach the bid. If the seller does the work, ask for the roofer's invoice with the scope before closing.
A credit lets you pick the roofer and check the work yourself. What to ask for after a home inspection covers how this line sits with the rest of your list. The buyer repair request letter template has the wording around it.
What if the seller says no?
Your choices are to accept the house as is, ask for a smaller credit or a price cut, or cancel inside your inspection window. A drain repair with a firm bid and a sagged deck with an open-ended bid are different decisions. When to walk away after a home inspection walks through it. Your contract sets the exact dates and terms, so confirm them with your agent.
Will home insurance cover a leak from ponding?
Don't count on it. One insurer, Liberty Mutual, says a policy "may cover a roof leak, but only if it's caused by a covered event such as fire, hail, or wind damage." It adds that most policies "typically won't cover roof leak repairs or damage that are a result of an aging roof, lack of upkeep, or general wear and tear." Ask your own insurance agent before your deadline.
What is the 25% rule for roofing?
The Bay Area roofer in the table calls it a practical cost rule: if repairs cover more than about 25% of the roof surface, replacing the roof often makes more sense. If your roofer's scope covers a large share of the flat section, ask for a replacement price too.
How do I know what the rest of my report is worth?
The ponding is one line, and your report has others. Get the roofer's bid on this one, then price the rest.
If the flat roof is one line of many, upload your inspection report to Kept and put the roofer's bid next to a price for everything else.
Sources
- Fixr, Flat Roof Repair Cost
- General Roofing, Flat Roof Repair Cost in California
- Professional Roofing (NRCA), Still Water Runs Deep
- Asphalt Roofing Manufacturers Association, Ponding Water Basics
- IKO, Why Is There Ponding Water on My Flat Roof?
- EPDM Roofing Association, Would a Manufacturer's Warranty Be Terminated Due to Ponding?
- Liberty Mutual, Roofs and Home Insurance
Cost figures are modeled from public wage and materials data unless a line says observed. Kept is accountable for the numbers on this page, and corrections go to support@usekept.com. How we price.