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Flat Roof Installation Cost

Flat Roof Installation Cost

National average
(1,500 sq.ft. PVC single-ply membrane roof)
Low: $4,500

(1,500 sq.ft. modified bitumen roof)

High: $12,000

(1,500 sq.ft. insulated PVC single-ply membrane roof)

Cost to have flat roof installed varies greatly by region (and even by zip code).
Get free estimates from roofers in your city.

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Flat Roof Installation Cost

National average
(1,500 sq.ft. PVC single-ply membrane roof)
Low: $4,500

(1,500 sq.ft. modified bitumen roof)

High: $12,000

(1,500 sq.ft. insulated PVC single-ply membrane roof)

Cost to have flat roof installed varies greatly by region (and even by zip code).
Get free estimates from roofers in your city.

The average cost of installing a flat roof is $5,000 - $11,500.

How Much Does It Cost to Have Flat Roof Installed?

While not as common as other roof types, flat roofs are often found on some styles of homes. A flat roof means that there is little to no pitch, meaning the slope of the roof, which allows water to stand or puddle on the roof. For this reason, a flat roof must be covered in a different type of material than other roofs. The most common type of flat roof material in the U.S. is polyvinyl chloride (PVC) single-ply membrane, which costs between $350 - $750 a square (100 sq.ft.) on average. The average range for a 1,500 sq.ft. roof is $5,000 to $11,500 with most homeowners paying around $7,500 for the project.

Flat Roof Costs

Flat roof costs
National average cost$7,500
Average range$5,000 - $11,500​

Minimum cost

Maximum cost$12,000

Types of Flat Roofs

Depending on the size of your roof, the average rainfall, and the style of the home, you may have a few different options for roofing materials. There are essentially four different types of flat roofs.

Single-ply Membrane

A single-ply membrane roof is generally the most popular. They can be made of PVC, other plastic, or rubber, such as ethylene propylene diene terpolymer (EMPD), and are quick and easy to install. They are heated and stretched across your roof and adhered using either a solvent adhesive or modified bitumen 1 or torched to the roof. Some types may even use metal anchors. They can last up to 40 years and, typically, hold up better to rainfall and other elements. They cost between $200 to $700 a square on average.

Single-ply membrane flat roof

Modified Bitumen

A modified bitumen roof is made up of sheets that are comprised of multiple layers, including bitumen, or tar. They are generally heated with a blow torch when rolled out onto the roof, which adheres them in one step. You will have more seams with this style of roof, but they are fairly easy to install and durable once finished. They only last 10 - 15 years, however, which is why they are less common. They cost between $200 to $500 a square.

Modified flat roof

Built-up Roof (bur)

Built-up roofs are some of the first types of flat roofs and pre-date modified bitumen roofs, which were designed to replace BURs. This roofing stacks multiple layers of membrane with bitumen between them, with a final reflective coating. They may be covered in rocks or crushed stone and are mostly seen on commercial buildings with very few residential settings. They last around 10 - 12 years and are time-consuming to install. They cost around $200 - $700 a square.

Built-up flat roof

Metal Roofs

Metal roofs are also much less common than they once were. Corrugated tin roofs were sometimes used on flat buildings because they were very durable and long-lasting. They can be very noisy, however, and older style roofs tended to rust. They can last decades when well-maintained and have a wide range of associated costs depending on the type of metal used, with prices ranging from $300 - $1,500 a square.

Metal flat roof

Pros and Cons of a Flat Roof

Flat roofs are less common than other types of roofs, mostly due to their disadvantages. Flat roofs do not allow rain or snow to easily run off, so they tend to stay wetter than other roofs. They may also hold more snow for longer and are difficult to clear. This can mean that they require more maintenance than roofs with a higher slope.

However, a flat roof is often less expensive, both to build and finish. And, it can also give some contemporary homes a sleek appearance, and in some instances, a flat roof can also be used as a garden or recreational area for the residents. It is also possible to plant on a flat roof, creating a green roof system.


Because flat roofs usually have little to no pitch, it is important that they are insulated against moisture. Some types of flat roofing material, like metal, also require insulation to help deaden the sound. Many homeowners also prefer to use a type of insulation to help improve energy usage on the roof. Generally, a rigid insulation board should be used as part of the roofing construction and may be applied over or under the roofing deck. Either extruded polystyrene (XPS) or insulated panel system (IPS) insulation can be used, provided that the insulation is breathable and developed for moisture management.

Installation Process

The installation process for a flat roof varies depending on the type of roof installed. Single-ply membrane roofs, no matter what they are made of, are generally heated, stretched, and adhered directly to the roof in a single layer. This is the fastest and easiest method of installing a flat roof.

Modified bitumen roofs will be rolled out and torched or heated with a blow torch as they are rolled onto the roof, sealing them in place. The edges are usually overlapped and heated together to help form a tight seam.

Built-up roofs have multiple layers laid, then coated in bitumen, with each one being placed on top of the next. They are generally sealed and topped with stone as the last layer.

Metal roofs are installed similarly to other metal roofs, with the panels laid out and interlocked together at the seams.

Labor Costs

Labor makes up the bulk of the installation costs for a flat roof. While the material itself may cost around $1 - $2 a square foot, labor generally costs between $3 and $7 a square foot. The total cost of the labor is generally based on the material. Single-ply membranes are the least expensive to install, while a built-up roof can be labor-intensive.

Other issues that may impact the cost of the labor can be the condition of the roof, whether you have any cuts in the roof for lights or a chimney, and whether the roof needs to be reinforced to hold things like an air conditioner unit. In these instances, labor may climb as high as $10 - $15 a square foot.

For a single-ply membrane roof, labor costs will be around $3,000 - $5,000 out of the $7,500 total.


Flat roofs generally require more maintenance than a sloped or pitched roof. This includes annual inspections to look for issues, such as cracks or breaks, along with keeping the roof clean and free of debris. If you notice leaks, address these as quickly as possible, usually through sealing the roof, to help prevent the problem from spreading. If you have overhanging trees, you may also want to have those trimmed back. In snowy climates, ensure that you have the roof shoveled regularly to prevent the weight from becoming too much for the roof structure.

Enhancement and Improvement Costs

Additional Layers

Not every flat roof can be built up in additional layers, but BURs can. More layers can increase longevity but expect to pay another $2 a square foot for added layers.

Roof Sealant

Depending on the roof type, you may be able to apply roof sealant to help prevent leaks and extend its lifespan. Sealants cost anywhere from $50 - $500, depending on the type and application.

Extra Underlayment

Roofs need a type of underlayment or membrane to help protect the deck. Depending on the type of roof, you may want an additional underlayment or rigid insulation underneath. This can add anywhere from $70 to $2,000 to the cost of the project.

Old Material Removal

Depending on the condition of your existing roof, you may need to have it stripped before new roofing can be installed. Sometimes this is included in the cost of the project. At other times, you may pay an additional $0.50 - $1.00 a square foot.

Green Roof

Green roofs are a great way to insulate your home or building and help manage stormwater runoff. They come in three different types and can be constructed of plants placed directly on the roof or made of modular planters. They can be very expensive, so expect costs to start at $5,000 and go as high as $15,000 additional.

Penetration Flashing

If you have chimneys, skylights, curbs, or other penetrations in the roof, you need to line them with flashing. Flashing costs between $20 to $100, depending on the type and placement.

Additional Considerations and Costs

  • Flat roofs need to have annual inspections to check for cracks and waterflow. Standing water or cracks may signal a need for repairs.
  • Flat roofs need ventilation, like a pitched roof. A flat roof vent costs between $300 and $600 on average, while a roof drain can cost $40 - $100.
  • Flat roofs, in general, do not increase the resale value of the home, but having a roof in good condition helps your home maintain its value.
  • Different flat roofs do better in different climates. White thermoplastic polyolefin (TPO) single-ply membranes tend to do best in hot climates, while rubber roofs and bitumen do better in cold climates.
  • Some areas require permits for roofing while others do not. Always check with your town or city hall to find out if you need a permit for this job.


  • What is the best material for a flat roof?

Single-ply membrane roofs last the longest, with PVC being the most popular.

  • How long do flat roofs last?

Depending on the material, a flat roof can last 10 - 40 years.

  • How often should you coat a flat roof?

This depends on its condition and the type of roof. Generally, they do not need to be coated unless you notice cracks.

  • How do you maintain a flat roof?

Flat roofs should be inspected annually, checked for cracks, and sealed as needed. ​

  • Can flat roofs be repaired?

Generally yes, a flat roof can be sealed to stop water damage and leaks.

  • Is it safe to stand on a flat roof?

This depends on the condition of the roof, and you should always have the roof inspected before standing on it.​

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Remodeling Terms Cheat Sheet

Definitions in laymen's terms, cost considerations, pictures and things you need to know.
See full cheat sheet.
glossary term picture Bitumen 1 Bitumen: A viscous, black mixture of hydrocarbons often used for roofing and waterproofing. It is also used in asphalt for paving roads

Cost to have flat roof installed varies greatly by region (and even by zip code). To get free estimates from local contractors, please indicate yours.

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