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How Much Does a Flat Roof Replacement Cost?

Written by

Leroy Whitt

Flat roofs are generally associated with commercial buildings, and it’s true, they are commonly the way to go for larger places of business where it would be much more difficult to install a slanted, thatched roof. But flat roofs have a lot to offer as they require less materials and take less time than a pitched roof.

Do you need of a flat roof replacement, but unsure where to start?

Whether it’s the cost-effectiveness of installing a flat roof or a sleeker, modern look, there are plenty of reasons to consider a flat roof. Whether you already have or your current business’s roof is in need of a replacement, we’re here to lay out the details of cost, installation, and more.

When it comes time for a flat roof replacement, you’ll want to know what your options are both financially and material-wise. In this article, we’ll uncover how much a flat roof replacement costs and everything in between.

Flat Roofs: Explained

aerial view of flat roof replacement newly installed

If you’re considering a flat roof in place of a traditional roof, the first thing you need to know is that flat roofs aren’t necessarily flat. They’re pitched at about 10 degrees or less, and while they can be made from several different types of materials, they always include a special waterproof membrane to keep moisture out. 

Here are a few other important things to know about flat roofs:

  • They’re also referred to as single-ply or single-layer roods
  • They’re cheaper to install and repair
  • They’re easier to maintain 
  • They’re energy-efficient
  • They’re incredibly versatile and are often used to plant rooftop gardens

The only downside to a flat roof is that they don’t last as long as their sloped counterparts, usually between 10 and 15 years. However, there are some flat roofing materials that can last for decades.

The Cost of Flat Roof Replacement

closeup of roofing contractor installing flat roof replacement

The average cost of a flat roof — which includes materials and labor — will run you between $4 and $13 per square foot. However, your flat roof replacement cost will vary based directly on the material you choose.

Here’s a quick materials breakdown:

  • Metal flat roofing: $4-$30 per square foot
  • Modified Bitumen: $4-$8 per square foot
  • Built-Up Roofing (BUR): $4-$10 per square foot
  • Rubber Membrane Roofing: $4-$13 per square foot
  • Singly-Ply Membrane: $4-$7 per square foot
  • Thermoplastic Polyolefin (TPO): $3.50-$14 per square foot
  • Fiberglass or GRP: $4-$6 per square foot

Other Factors in Flat Roof Replacement Costs

The primary things you have to think about when it comes to the cost of your flat roof replacement include:

  • The materials
  • The size of your roof

These two things contribute to the majority of the cost of your new flat roof. Of course, there are several other factors to think about, including:

Your Drainage System

closeup of flat roof drain installed by roofer

Flat roofs have special draining systems to ensure that water drains properly from them. When you’re replacing a flat roof, you’ll also have to have the drainage system replaced, and the cost of replacing this system can vary depending on the system type and any repairs needed.

Generally speaking, this portion of the replacement can cost anywhere between $600 and $1,000.


Labor costs are determined by the square foot for flat roof installations. On average, labor will cost:

  •  Between $3 and $7 per square foot for the primary construction
  • An additional $1-$2 per square foot for additional layers

Some roofers may charge by the hour instead — usually between $40 and $80 per hour of work. 

Material Type

flat bitumen roof replacement using torch

As noted above, the material you choose for your flat roof will have the greatest impact on the total replacement cost. Fortunately, there is a material type to suit all budgets, and while some materials are better than others, you don’t have to sacrifice quality to suit your budget.

For example, Modified Bitumen is one of the most cost-effective materials you can get for a flat roof, and it will last up to 20 years with proper installation and maintenance.  

Permits and Inspections

Your municipality or county will determine whether you need a permit or inspection to replace your flat roof. This is because electrical work, plumbing, and other structural work may be required to replace your roof. This includes the flat roof itself.

Something as simple as permits can have a large impact on both the cost and timeline of your roof replacement. The cost of these permits will vary based on things like:

  • Your location
  • The size of your roof
  • The complexity of the project 

Your roofing contractor will obtain the permit by contacting the proper city or county office, and you can expect to pay:

  • $75 for the permit
  • $100-$600 for the inspection (if necessary)

Removal of Your Old Roof

closeup of roofer performing flat roof replacement

Removing your existing roof is the first thing your contractor and crew will need to do to get the project started. This job is referred to as a “tear-off,” and it’s typically included in the $3-$7 per square foot labor costs.

Be sure to discuss this with your roofer and ensure there are no hidden fees regarding this part of the job in your roofing contract. Otherwise, it may cost more.

Roof Sealant

Once the new flat roof has been completely replaced, your roofer will need to seal it with a special sealant to protect it from the elements — especially the sun’s harsh UV rays or flat roof leakage. Sealants also help support shingle permeability, which adds an extra preventative layer to keep moisture from seeping in.

A regular, run-of-the-mill sealant can run you anywhere between $50 and $1,000, depending on the other components of your roof. However, sealing a flat roof is much cheaper compared to sealing a roof with a steep slope.

Vent Installation

closeup of flat roof vent installation

Roof vents allow air to flow through your attic or access space just below your roofing. They also allow rainwater to escape from the roof, which is essential to keeping your roof in good working condition. 

Therefore, roof vents will have to be either replaced or installed if they are missing or damaged. This generally costs between $300 and $600.

Ready For a New Flat Roof?

Replacing your flat roof is a no-brainer, as long as you’re sure of the type of materials you want used. Of course, if you’re converting the roof of your commercial business from steep-sloped to flat, there’s a bit more to consider cost-wise.

The professional roofers at Whitt’s Quality Roofing can help you with everything from choosing the right materials to budgeting for your flat roof replacement. Get in touch with us today to schedule a free inspection, and we’ll answer your questions in person!

Leroy Whitt

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