How Much Does a Flat Roof Cost to Replace?

Luca Clements October 23, 2026

Replacing a flat roof typically costs about $4 to $14 per square foot installed, depending mostly on the membrane. That puts a 400 square foot garage or addition roof at roughly $1,600 to $5,600 and a 1,000 square foot roof at about $4,000 to $14,000. Cost guides disagree on the details, so treat the ranges as a starting point for quotes.

Flat roof cost to replace, by membrane

Membrane	Installed per sq ft	For a 400 sq ft roof
EPDM	About $4 to $13	$1,600 to $5,200
TPO	About $4 to $14	$1,600 to $5,600
PVC	About $5 to $16	$2,000 to $6,400
Modified bitumen	About $4 to $8	$1,600 to $3,200

The figures combine HomeGuide and Fixr’s 2026 guides. HomeGuide’s ranges sit lower (EPDM $3.50 to $10, TPO $4 to $10, PVC $5 to $12, modified bitumen $4 to $7.50) and Fixr’s run higher. The membrane differences are real, but the installer and the detailing move the total as much as the material does, as EPDM, TPO and modified bitumen compared explains.

Cost by roof size

At $4 to $14 per square foot:

Roof area	Typical installed cost
200 sq ft (porch)	$800 to $2,800
400 sq ft (garage or addition)	$1,600 to $5,600
800 sq ft	$3,200 to $11,200
1,200 sq ft	$4,800 to $16,800

Small roofs tend to sit toward the upper end because setup, access and minimum charges are spread over fewer square feet.

What moves the price

Tear-off. Each extra layer of old roofing adds labor and disposal.
Insulation. Tapered insulation, used to build slope toward the drains, costs more than flat boards.
Drainage work. New drains, an overflow scupper or re-sloping add to the quote; ponding water is the usual reason.
Deck repair. Rotten sheathing is replaced at roughly $70 to $150 a sheet installed, and nobody can see it until the old roof is off.
The warranty. A manufacturer-backed warranty needs an approved installer, who may charge more.

The effect of skylights, curbs and parapets on the price is covered in the flat roof comparison above.

Repair, recoat or replace

Repairs run about $2.50 to $10 per square foot of roof repaired (HomeGuide, 2026). A liquid coating can extend the life of a sound roof, and the roof coating calculator works out how much to buy. Replacement is the better spend once repairs approach 25 to 30 percent of its cost and the roof is in the second half of its life; how long a flat roof lasts lists the signs.

Flat roof versus pitched roof cost

At $4 to $14 per square foot, flat roofing sits above basic asphalt shingles ($3.00 to $7.00 for 3-tab to architectural) and overlaps the dearer pitched materials. Cost per square foot and how much a new roof costs cover the pitched side.

How to price your own roof

Measure the roof, then add the upturns at walls and the edges, since the membrane has to cover more than the roof itself. The flat roof membrane calculator does that, and the roof replacement cost estimator multiplies a local price per square foot by the area. Then get three quotes on the same scope, and ask each what is being done about drainage, insulation and the warranty, so the quotes can be compared fairly. The roof quote calculator turns each one into a price per square.

More flat roof guides

The flat roof membrane calculator and roof coating calculator work out the quantities.

More roofing cost guides

The roof replacement cost estimator, roof quote calculator and roof financing calculator work from your own numbers.

Conclusion

A flat roof cost to replace of $4 to $14 per square foot is a wide range because the membrane, the roof’s size and the drainage work all move it. Price the area, add the extras that apply to your roof, and let local quotes narrow the figure. Use the table by roof size to check that a quote falls inside a sensible range.