Flat roof replacement cost.
Flat and low-slope roofs are priced by membrane type and area. Common on modern homes, additions, and garages.
Flat roof replacement cost by type
| EPDM rubber | $6,000 – $13,500 |
| TPO | $7,500 – $16,500 |
| PVC | $10,500 – $21,000 |
| Modified bitumen | $6,000 – $12,000 |
Typical installed range for a 1,500 sq ft project. Adjust the estimator above for your own size and options.
You are buying a system, and the membrane is a third of it
A flat roof quote covers deck prep, insulation, a cover board, the membrane, flashing, and terminations. The membrane itself is only about 30–40% of the money; insulation, fasteners, adhesive, and skilled labor are the rest. Installed, EPDM runs roughly $4–$8 per square foot, modified bitumen $4–$8, TPO $5–$9.50, and PVC $6–$12. Two bids on the same building can sit thousands apart purely on insulation thickness and membrane mil, so compare specifications line by line rather than bottom lines.
What moves the price on this one
Membrane thickness, quoted in mils
Single-ply membranes come in 45, 60, and 80 mil, and 60 mil is the common standard. On TPO, 60 mil runs roughly 15–25% more installed than 45 mil, and 80 mil roughly 25–40% more. The extra thickness buys puncture resistance and better wind-uplift performance, which matters most on any roof that people or HVAC technicians walk on.
How the membrane is attached
Mechanically attached, using fasteners and plates through the insulation, is the most economical. Fully adhered bonds the whole sheet down and performs better under high wind. Ballasted holds the membrane with stone or pavers, which is cheap and adds roughly 10–20 pounds per square foot of load while making leaks harder to trace. The method changes both the price and the wind rating, so it belongs in the bid.
Seam technology, where flat roofs actually fail
TPO and PVC seams are hot-air welded, producing a bond stronger than the sheet itself. EPDM seams are bonded with tape or adhesive, which tests far weaker. EPDM compensates by coming in much wider sheets, so there are fewer seams to begin with. That tradeoff, welded-and-many against bonded-and-few, is the honest way to compare the two.
Slope and ponding, which get priced as insulation
Design practice and most codes call for a minimum quarter inch per foot of fall to drains, and standing water should clear within roughly 48 hours. Where the deck does not do that, tapered insulation builds the slope into the assembly at roughly $2.00–$4.00 per square foot against $1.50–$3.00 for flat polyiso. Drainage corrections are the most valuable thing a re-roof can fix and the easiest thing for a cheap bid to skip.
What is already wet under the old roof
Saturated insulation does not dry out on its own. If core cuts or a moisture survey find wet insulation, it has to come out, which converts a recover into a tear-off. Recovering is genuinely cheaper, since tear-off adds roughly $1–$2 per square foot, but it only works on a dry assembly, and most codes cap the total number of layers at two.
What the quote has to spell out
- Membrane type and thickness in mils for the field of the roof
- Attachment method: mechanically attached, fully adhered, or ballasted
- Insulation type, thickness, and resulting R-value, plus whether a cover board is included
- Whether tapered insulation, new drains, crickets, or scuppers are included to correct standing water
- Tear-off or recover, and how many layers are already on the roof
- Flashing and termination detail at parapets, curbs, and every penetration
- Warranty type: material only, or a manufacturer system warranty covering labor, and the inspections it requires
Where this goes wrong: A quote priced on the membrane with no insulation specification. Insulation carries the R-value, the energy code compliance, and a large share of the cost, and it is the easiest line in the job to quietly deliver at two inches where the drawings called for four. Nobody sees it again once the membrane goes down.
Flat roof replacement cost: FAQ
How much does flat roof replacement cost?
Flat roofs run about $4 to $14 per square foot installed depending on membrane. A 1,500 sq ft flat roof costs roughly $6,000 to $21,000.
Which flat roof membrane lasts longest?
PVC and TPO are single-ply membranes that resist heat and last 20 to 30 years. EPDM rubber is cheaper and proven but darker, which absorbs more heat.
What drives flat roof cost up?
Tear-off of old layers, poor drainage that needs tapered insulation, roof penetrations, and hard rooftop access all add cost.
What is the minimum slope for a flat roof?
Flat roofs are not flat. Design practice and most codes call for at least a quarter inch of fall per foot toward drains, and water should clear within roughly 48 hours. Where the structure itself cannot be re-pitched, tapered insulation creates the required slope inside the roof assembly instead.
Should I recover my flat roof or tear it off?
Recovering skips tear-off, worth roughly $1–$2 per square foot, and is legitimate when the existing insulation is dry, the deck is sound, and you are not already at the code layer limit. If core cuts or moisture readings show wet insulation, recovering seals the water in and the new membrane inherits the problem it was bought to solve.
Why does ponding water matter if the roof does not leak?
Because it shortens the roof's life before it shows up as a leak. Standing water adds structural load, keeps seams and adhesives permanently wet, accelerates UV and biological growth, and voids many manufacturer warranties outright. Multi-ply modified bitumen tolerates it better than single-ply membranes do, but no system is designed to sit under water.