Replacing a flat roof costs $300 to $1,100 per roofing square installed, or $4,000 to $16,800 for a typical job. The spread is not about your house. It is about which of ten different systems goes on it, from rolled asphalt at the bottom to metal and concrete at the top. This page prices each one and explains what separates them.
These are national estimates, not quotes. They come from a published cost survey, not from bids on your building. What you pay depends on your region, your roof and your contractor. Get at least three written estimates. The methodology page lists every source used and the rounding rules applied here.
$3 to $11 per sq ft × 100 sq ft
implies a roof of about 13 to 15 squares
rolled asphalt · shortest lifespan
low-slope metal · concrete close behind
That last point is the one thing that makes flat roofs easier to estimate than pitched ones: there is no pitch multiplier to apply. Your roof area is your footprint.
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What counts as a flat roof
Almost nothing called a flat roof is actually flat. A roof that held water would fail quickly, so a working flat roof is built with a slight fall towards drains or scuppers. The industry term is low-slope, and the cost figures on this page apply to anything too shallow for shingles.
The dividing line is a pitch of about 2:12. Asphalt shingles generally need at least that much slope, with extra underlayment between 2:12 and 4:12. Below 2:12, shingles are not an option and the roof has to be covered with a membrane, a sprayed coating, or a standing-seam metal or concrete system instead. If you are not sure which side of the line your roof falls on, measure it with the roof pitch calculator before you read the prices below, because it decides which cost guide applies to you.
That threshold is also why flat roofing is priced differently. On a pitched roof you are buying overlapping pieces that shed water downhill. On a low-slope roof you are buying a continuous waterproof skin, and the price is driven by what that skin is made of and how many layers it has.
Flat roof replacement cost by material
These are installed costs from our cited source, converted from cost per square foot to cost per roofing square and rounded to the nearest $5. Every conversion here is exact, so nothing was lost in the rounding.
| System | Per square installed | Per sq ft |
|---|---|---|
| Rolled asphalt | $200 to $500 | $2.00 to $5.00 |
| Spray foam | $350 to $700 | $3.50 to $7.00 |
| Built-up, tar and gravel | $350 to $750 | $3.50 to $7.50 |
| Fiberglass (GRP) | $350 to $750 | $3.50 to $7.50 |
| Modified bitumen | $400 to $750 | $4.00 to $7.50 |
| EPDM rubber membrane | $350 to $1,000 | $3.50 to $10.00 |
| TPO membrane | $400 to $1,000 | $4.00 to $10.00 |
| PVC membrane | $500 to $1,200 | $5.00 to $12.00 |
| Concrete | $400 to $1,500 | $4.00 to $15.00 |
| Metal, low-slope | $500 to $1,600 | $5.00 to $16.00 |
Read the low ends and the high ends as two different stories. At the bottom, six of these systems start within $200 of each other, so the cheapest quote you get will not usually be decided by the material. At the top, the range runs from $500 to $1,600, and that is where the choice starts to matter financially. Sorting by the low end, as the table does, is the wrong way to shop; sorting by what the roof has to survive is the right way.
The four families, and what you are actually choosing between
Ten products is a misleading way to see this market. They fall into four families, and the decision is usually between families rather than within them.
Multi-ply asphalt: built-up and modified bitumen
Built-up roofing, the tar and gravel roof, is the oldest system here: alternating layers of bitumen and reinforcing fabric, topped with gravel. Modified bitumen is its modern relative, supplied in rolls with polymer added to the asphalt so it stays flexible. At $350 to $750 and $400 to $750 per square respectively, they sit in the middle of the market, and their appeal is redundancy. Several layers means a puncture does not immediately become a leak.
Single-ply membranes: EPDM, TPO and PVC
This is where most residential low-slope work now goes. One sheet of synthetic material, seamed together on site. EPDM is a rubber, usually black, at $350 to $1,000 per square. TPO is a plastic, usually white and therefore reflective, at $400 to $1,000. PVC is the most expensive of the three at $500 to $1,200 and the most resistant to grease and chemicals, which is why it is common over kitchens.
The three overlap so heavily in price that cost is rarely the deciding factor between them. Seam method, colour and what the roof is exposed to usually decide it. What they share is that the seams are the weak point, so the quality of the installation matters more here than the material choice does.
Sprayed and liquid systems: spray foam and fiberglass
Spray foam at $350 to $700 per square and fiberglass at $350 to $750 are applied as liquids and cure into a seamless surface, which removes the seam problem entirely. Foam adds insulation as part of the roof. Both need recoating on a maintenance schedule to survive UV, so the purchase price is not the whole cost, and neither the recoat interval nor its price is published by our source.
Structural systems: metal and concrete
Low-slope metal at $500 to $1,600 per square and concrete at $400 to $1,500 are the expensive end. Neither is really a membrane; they are structure and roof at once, which is why they cost what they do and why they are rarely a retrofit on a house built for something lighter. For sloped metal roofing, which is a different set of products and prices, see the metal roof cost guide.
Working out your own number
Flat roofs are the easiest roof on this site to estimate, and the reason is geometry. Every other cost guide here needs a pitch multiplier, because a sloped roof has more surface than the house underneath it. A 6:12 gable is 1.118 times its own footprint. A low-slope roof is so close to level that the multiplier is effectively 1, so:
Squares = footprint length × width ÷ 100. Then multiply by a per-square figure from the table above.
A 1,500 square foot flat roof is 15 squares. At $300 to $1,100 per square that is $4,500 to $16,500, which sits almost exactly on the published national total of $4,000 to $16,800. Running that backwards is a useful check on the national figure: it implies a roof of roughly 13 to 15 squares, so if your building is much bigger than that, the headline total understates your job and the per-square figure is the one to use.
Two things still need adding to your own number. Tearing off the old roof is extra, and on a low-slope roof there may be several layers and wet insulation to remove. And drainage work, new drains, scuppers or tapered insulation to correct a ponding problem, is a separate line that no per-square figure covers. Ask for both to be itemised.
If your roof is not actually low-slope, the roof area calculator will apply the right multiplier for you, and the roofing square calculator converts area into squares with a waste allowance.
What we cannot tell you, and why
Our source publishes one lifespan figure for this entire category: 5 to 60 years. That is the widest range of any roof type on this site, wider than metal at 30 to 80 and asphalt at 15 to 30, and it is the honest answer to how long a flat roof lasts, which is that it depends entirely on which system you bought.
It also means we cannot give you the cost-per-year table that appears on the shingle and metal guides. Dividing a price by a 12-fold lifespan range produces a number so vague it would mislead rather than help. Rolled asphalt is the cheapest system here at $200 to $500 per square, and our source states plainly that it also has the shortest lifespan, so it is very likely the worst value per year of the ten. We cannot show you by how much, because the figures to do that arithmetic are not published, and we are not going to estimate them.
What follows from that is a practical instruction rather than a number. Ask every contractor for the manufacturer, the product name and the warranty length of the membrane they are quoting, and compare those rather than the headline price. On a flat roof, the warranty is the closest thing to a published lifespan you will get.
Three other figures are missing for the same reason. Our source does not price tear-off separately for low-slope roofs, does not publish recoating intervals or costs for spray foam and fiberglass, and does not price drainage work. None of those appear on this page.
Repairing a flat roof instead
Low-slope roofs are among the cheaper roofs to repair. A minor repair runs $200 to $500, and section work runs $250 to $1,000 per square, which is the lowest per-square repair figure of any roof type our source lists. A single-ply membrane can often be patched with the same material and a heat weld or adhesive, which is genuinely a repair rather than a visible patch.
The catch is diagnosis. Water travels along the underside of a flat deck before it appears inside, so the wet ceiling is frequently nowhere near the hole. That makes flat roof leaks harder to find than pitched roof leaks, and it is why an inspection is worth paying for before you authorise work.
The repair-or-replace test itself is the same on any roof, and it is set out with the arithmetic on the roof repair cost guide. Ponding water that never drains is the one flat-roof-specific signal that a patch will not fix, because it points at the fall of the roof rather than the covering on top of it.
What this page leaves to the other guides
- Pitched roof replacement, cost by house size, tear-off, decking and what makes quotes differ: roof replacement cost guide.
- Sloped metal roofing, standing seam through to copper, which is a different product set from low-slope metal: metal roof cost guide.
- Repair pricing by problem and the repair-versus-replace test: roof repair cost guide.
- Asphalt shingle grades, if it turns out your roof is steep enough for shingles after all: shingle roof cost guide.
Sources used on this page
- HomeGuide roof replacement cost guide, dated November 7, 2025. The flat roof replacement cost table for all ten systems, the $3 to $11 per square foot headline, the $4,000 to $16,800 total, and the 5 to 60 year lifespan for the flat, rolled and built-up category.
- HomeGuide roof repair cost guide, dated February 9, 2026. Repair figures for flat, rolled and single-ply roofs.
- National Roofing Contractors Association and the Asphalt Roofing Manufacturers Association. Used for installation conventions, including the minimum slope below which asphalt shingles are not used.
Per-square figures are the published cost per square foot multiplied by 100 and rounded to the nearest $5. Every conversion on this page is exact. The square-count arithmetic is our own, shown in full so you can check it. The methodology page explains how sources are used across the site and how often figures are reviewed.
Related guides and calculators
- Roof Replacement Cost: the whole job, by size and by material, and what moves the price.
- Roof Repair Cost: repair pricing by problem and the repair-versus-replace test.
- Shingle Roof Cost: three-tab, architectural and luxury asphalt compared.
- Metal Roof Cost: corrugated, standing seam, metal shingle and the premium metals.
- Roof Pitch Calculator: find your pitch and check whether your roof is low-slope.
- Roof Area Calculator: turn footprint, pitch and overhang into true roof surface area.
- Roofing Square Calculator: convert area into squares with a waste allowance.
Flat roof replacement cost FAQ
How much does it cost to replace a flat roof?
A flat roof costs $300 to $1,100 per roofing square installed, or $3 to $11 per square foot, which works out at $4,000 to $16,800 for a typical job. The published total implies a roof of about 13 to 15 squares, so on a larger building use the per-square figure instead.
What is the cheapest flat roof material?
Rolled asphalt, at $200 to $500 per square installed. Spray foam, built-up tar and gravel, and fiberglass follow at $350 per square at the low end. Our source notes that rolled asphalt also has the shortest lifespan, so cheapest to buy is not cheapest to own.
How much does a TPO or EPDM roof cost?
EPDM rubber membrane costs $350 to $1,000 per square installed and TPO membrane $400 to $1,000. PVC, the third common single-ply membrane, costs $500 to $1,200. The three overlap so heavily that price is rarely what decides between them.
How long does a flat roof last?
Our source publishes a single figure for the whole category: 5 to 60 years. That 12-fold spread is the honest answer, because lifespan depends entirely on which system was installed. Ask the contractor for the manufacturer, product name and warranty length, which is the closest thing to a published lifespan you will get.
What pitch counts as a flat roof?
Anything too shallow for shingles, which in practice means below about 2:12. Asphalt shingles generally need at least 2:12, with extra underlayment between 2:12 and 4:12. Below that the roof needs a membrane, a sprayed coating, or a metal or concrete system. Measure yours with the roof pitch calculator.
How do I work out how many squares my flat roof is?
Multiply the length by the width and divide by 100. Unlike a pitched roof, a low-slope roof needs no pitch multiplier, so the roof area equals the footprint. A 1,500 square foot flat roof is 15 squares.
How much does it cost to repair a flat roof?
A minor repair on a flat, rolled or single-ply roof costs $200 to $500, and section work costs $250 to $1,000 per square. That is the lowest per-square repair figure of any roof type. The hard part is finding the leak, because water travels along the underside of the deck before it shows inside.
Are these prices quotes?
No. They are national estimates from a published cost survey. Your price depends on your region, your building and your contractor, and tear-off and drainage work are extra. Get at least three written estimates.