How Much Does Flat Roof Replacement Cost?

Lawrence Bonk
Written by Lawrence Bonk
Updated May 23, 2022
New two-story home with flat roof
Photo: irina88w / iStock / Getty Images

The average cost to replace a flat roof, including materials and labor, is $3,100 to $9,600

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There are many benefits to a flat roof, including energy efficiency, increased outdoor living space, and a great overall aesthetic. They are also relatively easy to install compared to their sloped counterparts. The cost to replace a flat roof averages around $6,200, though this price fluctuates depending on your chosen roofing materials, the size of your roof, and some other hidden variables.

How Much Does It Cost to Replace a Flat Roof Near You?

Flat roofs look sleek and modern, making them a great choice for homeowners who are looking for this style. Material costs and labor vary by location, so it’s important to speak with a local roofer to get an accurate quote.

Certain areas, such as California and Florida, have unique regulatory requirements that could increase the cost of your roof replacement. Certain materials are harder to source in some parts of the country. For instance, GRP is tougher to get in Seattle, as this material is only installed during dry days. 

Here are some price estimates for flat roof replacement in several locations:

  • Minneapolis: Average cost of $3,670 with a typical range between $1,720 to $5,630.

  • Los Angeles: Average cost of $5,170 with a typical range between $2,780 to $7,670.

  • Miami: Average cost of $7,110 with a typical range between $3,730 to $10,610.

  • Long Island, NY: Average cost of $5,840 with a typical range between $3,110 to $9,370.

  • Denver: Average cost of $5,440 with a typical range between $2,690 to $8,420.

Flat Roof Replacement Cost Breakdown

Flat roofs are prone to damage, as dirt and debris can easily accumulate on the flat surface, and the lack of a slope will complicate your drainage options. In other words, a flat roof won’t last quite as long as a sloped roof, sometimes failing in just a decade.

If something damages the roof beyond repair, you’ll need to hire a local roofing contractor to get it replaced. You’ll spend your money in an even split between materials and labor when replacing a flat roof.

Some roofers may charge by the square instead of measuring out by the foot. A roofing square typically equals 100 square feet, and installation costs $250 to $350 for each one. Other factors impact the overall cost of replacing a flat roof, including the removal and disposal of old roofing materials, putting down additional layers of underlayment, and adding ventilation and roof drains. 

Here’s a detailed breakdown of how you can expect to spend your money when hiring a local roofer to replace a flat roof:

Labor

Roofers charge around $40 to $80 per hour, and a flat roof will take around five days of work to complete, depending on the size and complexity of the job. This puts your labor costs at $1,600 to $3,200. Some roofing materials, such as built-up tar, are more time-consuming to install, so this will impact the overall cost of labor.

Removal of Old Roofing Materials

If you are replacing a damaged roof, it is likely the old roofing materials will need removal and disposal. Some contractors will wrap this up in the overall quote, but others will charge extra. The job averages $1,000 to $1,500, at around $1 to $5 per square foot of roofing material. Talk to your contractor and ask how much disposal is adding to your overall bill.

One of the advantages of flat roofing is that you can overlay the existing roof instead of tearing it off. But if you have rotten decking that needs repaired, you might not discover it if you do an overlay. Additional layers do add R-value to your roof, so you’ll need to make sure that the structure itself can handle the additional weight of another layer. Your roofing contractor should be able to discuss with you if a layover is a viable option.

How Much Does It Cost to Replace a Flat Roof by Type?

There are many types of roofing materials to work with, each with its own cost estimates, advantages, and disadvantages. Before deciding on a material, talk to a qualified pro about which one is best for your individual needs. 

As a note, prices surged 5% to 10% in 2021, as demand for roofing materials increased significantly. Additionally, there have been delays in sourcing materials. Plan ahead.

Fiberglass

Fiberglass has increased in popularity in recent years, as it is relatively inexpensive, offers fantastic water resistance, and has a lengthy lifespan of 25 to 50 years if properly maintained. Fiberglass is not as durable as some materials, it is glass after all, so annual inspections are a necessity. You’ll pay $1 per square foot for the materials and $4 to $6 per square foot for the installation.

Rubber

Rubber flat roofs are highly resistant to warm weather and solar rays, making this material a great choice for sun-drenched climates. Rubber is relatively lightweight and can last 25 to 50 years if properly cared for. You’ll pay $4 to $13 per square foot for a rubber flat roof, but this price includes both labor and materials.

Thermoplastic Polyolefin (TPO) 

Thermoplastic Polyolefin (TPO) is a singly-ply system that lasts between 20 and 25 years, and can generally handle ponding water up to 72 hours. TPO is lightweight and reflective, and you can also get it in several colors, but the white is the most energy-efficient. It costs about $3 to $5 per square foot.

EPDM

Ethylene propylene diene monomer (EPDM) is a roofing material made from oil and natural gas byproducts. It is easy to install, which saves money upfront, but tends to fail after 10 to 15 years of use. It is available in various thickness options and in two colors, black and white. EPDM is used more in northern climates that have snow loads, and less in the south, where the conditions of heat and lack ran of rain cause EPDM to fail sooner. 

Black EPDM absorbs heat, which could impact your energy bill, while white EPDM features a cooling laminate layer. EPDM costs $5 to $13 per square foot, with the white variety falling on the higher end of this spectrum.

Built-Up Tar

As the name suggests, built-up tar layers slowly over time. This makes for a lengthy installation process but offers some distinct advantages over other roofing types. Tar is extremely resistant to fire and does not require too much maintenance. It also lasts about 30 years. You’ll pay $4 to $10 per square foot for both labor and materials. It’s important to note that built-up tar roofs aren’t very common anymore, though they were quite popular in the 1970s and 80s. Some roofers won’t take on a hot tar roof job anymore, and most liability insurance policies won’t cover it.

GRP

GRP, or glass-reinforced polyester, is a newer roofing type that addresses some of the downsides of fiberglass. This material is a blend of plastic and fiberglass that offers increased durability and increased resistance to the elements. They can be tricky to install, though, as the contractor will have to wait for a string of dry days. GRP roofs cost $4 to $6 per square foot, but that price reflects both labor and materials.

Modified Bitumen

Modified bitumen is a single-ply roofing material that is placed down in sheets. It’s been around since the 1960s, but until recently was primarily available for commercial locations. However, it is particularly easy to install and fully recyclable, making it a desirable choice to modern homeowners. 

There are some trade-offs here, as modified bitumen is not exceptionally water-resistant and will need replacement after 10 to 20 years. It costs $4 to $6 per square foot. 

Modified bitumen can also be a two-ply roof system, using a base sheet and a cap sheet. When it's a one-ply system the manufacturer warranty is generally about 12 years and with two-ply it is 15 years. Most pros recommend using a two-ply system. 

You also should not install modified bitumen on a roof with a slope less than 1:12, as it can’t handle ponding water and will fail if there is standing water on the roof.

There are some trade-offs here, as modified bitumen is not exceptionally water-resistant and will need replacement after 10 to 20 years. It costs $4 to $6 per square foot.

What Factors Influence the Cost to Replace a Flat Roof?

Exterior view of modern home with flat roof
Photo: Erik Snyder / The Image Bank / Getty Images

Replacing a roof is a complex procedure, and each home has unique needs. There are some other factors to consider when pricing out the cost to replace a flat roof.

Sealing the Surface

To simplify the maintenance process, apply a sealant or coating to your newly installed flat roof. This adds an extra layer of waterproofing and can increase fire resistance and overall durability. The quality of a coating can vary quite a bit—it's not always a long-term solution, but with the right product, it can be. Of course, it will also increase the cost of your project. Count on paying $400 to $1,600 extra for a sealant layer.

Ventilation and Roof Drains

Flat roofs are, well, flat, so having a good drainage setup is an absolute must. You may already have a decent drainage system if you’ve been living under a flat roof, but if you need to have drains or gutters installed or have some pre-existing drains rerouted, you’ll pay $600 to $1,000. 

Ventilation is also extremely important, as some flat roof materials can absorb heat, where it is then released into your home. Installing a single roof vent costs $300 to $650 on average.

Permits and Inspections

Depending on where you live, you may need to pay for a building permit to replace your flat roof. These permits cost between $250 and $500, though this price increases for roofs larger than 1,000 square feet. 

Additionally, you may want to hire a professional to conduct a final inspection after the roof has been replaced. This will ensure that the contractor did good work. Expect to pay between $120 to $300 for this inspection.

FAQs About Replacing a Flat Roof

How do I find a reputable contractor to replace a flat roof?

Replacing a flat roof is a significant investment, so you should take some time before deciding on a pro. Do all the research you can via the company’s official website, any social media accounts, and by checking with the Better Business Bureau. 

Don’t be afraid to reach out to the contractor’s previous clients for anecdotal information. Finally, give them a call and have some good questions to ask the roofers prepared ahead of time. A qualified professional will answer them with ease.

Should I purchase an extended warranty?

Many contractors offer extended roof warranties that go beyond the scope of the warranty offered by the materials manufacturer. Should you buy one? This depends on how long the coverage lasts and the cost of the warranty itself. 

You should also check on the specific coverage offered by the extended warranty, as some may exclude common maintenance and repair tasks.

Can I repair it instead of replacing the whole thing?

You can if the damage is not extensive enough to warrant a full replacement. Most contractors will perform a free inspection before giving you a quote, so you may just need some minor repairs. Patching small tears and performing other repair jobs cost $300 to $600, though larger overhauls cost $1,000 or more.

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