What is a Flat Roof and Why is it Used?

flat roof on house with a pool

While the majority of homes have pitched roofs, you may notice some homes have flat roofs. Not only are flat roofs affordable, they are also low maintenance and are the perfect roofing style for modern homes. But what is a flat roof and why is it used on some homes?

There are so many types of flat roofs: EDPM, TPO, PVC, BUR, GRP, MBS, SPF. If you are overwhelmed by all the confusing acronyms for flat roof options, here is a chance to learn about the different flat roofing materials, costs, pros and cons, and more. 

What is a Flat Roof?

To be considered a flat roof, a roof must be relatively level, a low-sloping roof with a tilt of 10-degrees or less. A flat roof should never be completely flat, otherwise water won’t be able to drain off the roof. 

Although the majority of flat roofs are made of asphalt and roofing felt, flat roofs can be made of many different types of materials:

  • Asphalt 
  • Concrete
  • Fiberglass
  • Metal
  • Rubber
  • Spray polyurethane foam
  • Tar

Types of Flat Roof Drainage Systems

Flat roofs must be set at a slight tilt, otherwise they will not be able to drain properly and water will pool on your roof. You want to avoid standing water on your roof, as it causes water damage and leaks.

There are some ways to make sure water is properly draining from a flat roof:

  • Inner drains. Also called internal or interior drains, these drains are placed at the center of the roof. Inner drains connect to hidden pipes and gutters underneath the surface of the roof that carry the rainwater off your roof to a gutter or downspout. 
  • Scuppers. One of the most common methods for flat roofing drainage systems is scuppers, which are openings in the sides of a wall that allow water to drain. Scuppers can be combined with gutters and downspouts to route excess water off the roof. 
  • Gutters. Having a gutter system carry water off your roof helps protect your home’s foundation from being damaged by rainwater erosion. 
  • Siphonic drainage systems. They prevent air from entering the drainage pipes, allowing gravity to transport large quantities of rainwater off the roof. They work best for large roofs. 
  • Tapered insulation. Tapered insulation adds more slope to your flat roof. This helps gravity properly drain water off your roof. 

Best Climate for Flat Roofs

One of the cons of flat roofs is that they are not the most adaptable to extreme temperature changes. While flat roofs can technically work anywhere, ideally they work best in warm, dry climates, and not areas with a lot of moisture, snow, ice, and freezing temperatures.

For the same reason that flat roofs have trouble draining rainwater, they also have trouble shedding ice and snow. On a sloped roof, gravity works against snow piling up and will knock down snow before it can tower too high. 

But on a flat roof, snow continues to pile on the roof. This makes flat roofs susceptible to collapsing in heavy snowfall.

What Are the Different Types of Flat Roofs?

Flat roof is a broad term for several different types of roofs. A flat roof merely refers to the angle of the roof being less than 10 degrees, not a reference to any specific roofing material

While most might generally think of flat roofs as plain rubber roofs, flat roofs actually come in a broader variety, so you will want to consider what would be the best material for you based on your budget, your home’s aesthetic, and your personal preference. Here is a quick list of the different types of flat roofing materials:

Built-Up Roofing (BUR)

A picture showing a flat gravel roof which is easy to clean
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The most commonly used type of roof is built-up roofing, which consists of sheets made of roofing felt and tar (or asphalt) topped with a layer of gravel or stone. BUR roofs have been used for over 100 years, making it a reliable and well-tested roofing material.

Concrete Roof

picture of a concrete roof in a diagonal pattern
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Concrete tile roofs are long-lasting with a life expectancy of up to half a century. However, it is a heavy roofing material that can put a lot of structural stress on your home. 

Ethylene Propylene Diene Monomer (EPDM)

EPDM roof with mountains in the background
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As the least expensive type of flat roof, EPDM is a rubber roof that comes in black or white. Because of its cheaper pricing, it is the most common commercial roofing type. It is best suited for cold climates. 

Glass Reinforced Polyester (GRP) 

Fiberglass roof
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GRP roofs are made of fiberglass. While they are easy to repair and maintain, they don’t do well with a lot of foot traffic. 

Green Roof

Flat roof covered in plants
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A green roof consists of a growing medium and plants, forming a rooftop garden for everyone to enjoy. This eco-friendly roof provides nature lovers with a rooftop garden. Depending on the size of plants you want, green roofs can be extensive, intensive, or semi-intensive. 

Metal Roof

Metal roof
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Metal roofs are expensive but they come with many benefits. Metal roofing is durable, energy efficient, low maintenance, customizable, and lightweight. 

Metal roofs are eco-friendly as they are recyclable, decrease the amount of tear-off waste, and help reduce urban heat islands. They have long lifespans, as some metal roofs last up to 100 years. 

Modified Bitumen Systems (MBS)

MBS roofs are made of tar and fiberglass coated with elastomeric. Instead of tar, some MBS roofs use asphalt instead. 

Polyvinyl Chloride (PVC)

PVC membrane roll on a roof
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PVC is a thermoplastic waterproofing membrane made of vinyl. It is flexible and easy to install. However, reroofing isn’t an option with PVC, as once it reaches the end of its lifespan you will need a complete roof replacement. Polyvinyl chloride is also known for being a durable and chemical-resistant roofing. 

Spray Polyurethane Foam Roofing (SPF)

A worker sprays polyurethane foam on a roof
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Spray roofs are sprayed onto your roof in liquid foam. This liquid then turns into foam and hardens. Every few years, it has to be applied with a protective coating to protect the roof from harmful UV rays, which will otherwise deteriorate the roof. It is easy to install and maintain. 

Thermoplastic Polyolefin (TPO)

TPO roofs are constructed from large sheets of polypropylene and rubber. The material is 100% recyclable, lightweight, and flexible. 

Why Are Flat Roofs Used?

A home with a flat roof
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You may have noticed that flat roofs are more prevalent on commercial buildings than homes, which typically have pitched roofs. You may be wondering what are the reasons that so many businesses find flat roofs a better alternative to sloped roofs?

There are many benefits to flat roofs.

Provide More Space

A roof doesn’t have to just be a house topper – it can be a recreational area for people to enjoy. Flat roofs can function as rooftop gardens, a place for a barbeque cookout, or an outdoor space to relax. Sometimes swimming pools can even be installed on a flat roof.  

Aside from being used as a place to hang out and chill, flat roofs also can be used for storage. 

Although flat roofs don’t provide interior storage space, some commercial or industrial buildings store HVAC units or ventilation systems on their flat roofs. A flat roof is also the perfect roofing style if you want to install solar panels


Flat roofs are relatively inexpensive compared to other roofing styles. Not only are the types of materials cheaper than materials for sloped roofs, but there is less surface area to cover than a sloped roof, which saves money on roofing materials. 

Increase Curb Appeal

Because people can’t really see a flat roof from ground level, it really puts a focus on the architecture of the home. A flat roof offsets a home from all the others around it that have pitched styles. 

Flat roofs are a great choice for homeowners looking for roofing with a contemporary touch, as flat roofs give homes a sleek, modern look.

Low Maintenance

Flat roofs are easily accessible, which makes them low maintenance and easy to repair. 

To clean a flat roof surface, just grab a broom or leaf blower to remove any debris off the roof. You can also use a vacuum to clear off debris. Additional upkeep includes unclogging the gutter system and trimming back any overhanging tree branches.

Avoid using a pressure washer for cleaning, as the rough jets of water can cause damage to your roof. Instead, use a hose and soap to rinse off your flat roof. 

Chlorine and sodium hydroxide can also be used to clean your roof, although be careful, since these chemicals can be harmful to the environment and they must be thoroughly rinsed off, otherwise they might damage your roof. 

Every so often, your flat roof needs to be recoated, as the protective coatings on flat roofing don’t last forever. Water problems such as ponding or leaking are a sign that your roof needs to be recoated. 

How often your roof will need to be recoated is dependent on age, type of material, and roof size. Usually, a flat roof needs to be recoated every five years or so. However, the older a flat roof gets, the more frequently it needs to be recoated. 

Although routine cleaning is an easy DIY job, recoatings are challenging and are best performed by a professional roofing contractor. You also can hire a roofing company for any cleaning, repair, or recoating jobs. 

Energy Efficient

Flat roofs are an energy-efficient option, particularly in warm climates. Flat roofing material is rigid and has a uniform membrane system, so it doesn’t have as many seams as pitched roofs. The lack of gaps provides good insulation and helps keep indoor temperatures stable. 

Quick to Install

Flat roofs require less roofing material, which makes the installation process easier and requires less labor. 

Flat roofing can be installed quickly, usually taking an average of one to two days for a roof to be installed. 

Make Roof More Accessible

The flat surface allows people to navigate a flat roof much easier than the difficult angles of a pitched roof. The accessibility of a flat roof makes it much easier to perform roof maintenance and repairs. 

Cons of a Flat Roof

snow on roof
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While there are many advantages to owning a flat roof, there are some drawbacks. 

Drainage Issues

One of the most prominent problems of flat roofs is they commonly have drainage problems and they’re susceptible to ponding water on the roof. 

Due to the gentle slope, flat roofs don’t drain as well as sloped roofs. Flat roofs will have to be checked if they are not draining properly, and standing water on a flat roof is a sign that it will need to be repaired. 

No Attic Space

Although flat roofs can be used as storage areas for outdoor HVAC units, they don’t provide any attic storage space. While this might not be a big deal for commercial properties, the lack of attic space might be a nuisance for homeowners who may need the additional storage for items inside their home. 

Snow Accumulation

Snow will keep piling up on a flat roof. With a sloped roof homeowners can count on gravity to pull down snow and keep it from piling too high on the roof. But flat roofs don’t have that benefit, and snow will continue to pile in heavy heaps on your roof. This puts immense structural pressure on your roof, which can be dangerous and lead to your roof collapsing if the weight becomes too much. 

Shorter Lifespans

Certain types of flat roofing have long lifespans, such as metal, EPDM, PVC, and green roofs. Those types of materials can last 20 to 30 years or more. But many flat roofs are made of less expensive materials that can’t stand up to the elements. For instance, modified bitumen has a lifespan of only 10 to 15 years.

Bad for Cold Climates

The ideal home for flat roofs are in warm, dry areas. Although flat roofs can work in colder areas, the majority of flat roofs work best in warm climates. There are certain types of roofing materials that do well in cold areas, such as metal roofs. 

How Much Do Flat Roofs Cost?

Prices for flat roof installations vary depending on the roofing material, but typically the cost of a flat roof ranges between $4,300 and $19,100. 

Like with all roofs, the cost depends on the size of the roof, the type of roofing material, and the building’s geographic location. Certain materials cost more, such as metal or green roofs, whereas other types of roofing will be much cheaper, like EPDM or a TPO roof. 

Flat Roof TypePrice Per Square Foot (labor and materials included)
Built-Up Roofing (BUR)$3 – $8
Concrete$4 – $8
Ethylene Propylene Diene Monomer (EPDM)$5 – $12
Glass Reinforced Polyester (GRP)$4 – $7
Green Roof$15 – $50
Metal$3 – $20
Modified Bitumen Systems (MBS)$3 – $6
Polyvinyl Chloride (PVC)$6 – $13
Spray Foam Roofing$4 – $6
Thermoplastic Polyolefin (TPO)$4 – $11

Unfortunately, at some point flat roofs will require repairs, so it will be necessary to budget for roof repairs, as well. Flat roof repairs tend to cost between $300 to $1,175. 

How Long Do Flat Roofs Last?

The life expectancy of a flat roof depends on the roofing material. On average, flat roofs last about 20 to 25 years, although certain types of flat roofs can last well beyond that. 

Flat Roof TypeLifespan
Built-Up Roofing (BUR)15 to 20 years
Concrete50 years
Ethylene Propylene Diene Monomer (EPDM)10 to 50 years
Glass Reinforced Polyester (GRP)25 to 50 years
Green roof40 to 50 years
Metal30 to 100 years
Modified Bitumen Systems (MBS)10 to 20 years
Polyvinyl Chloride (PVC)20 to 30 years
Spray Foam Roofing20 to 50 years
Thermoplastic Polyolefin (TPO)15 to 20 years

Maintenance and repairs are necessary to prolong your roof’s life and keep it in good shape. Without proper care and upkeep, a roofing system may underperform and fall short of reaching its expected lifespan.

FAQ About Flat Roofs

Can you apply shingles to a flat roof?

Shingles will not work on a flat roof surface. The fewer sealed points, the better, which is why it is necessary to use roofing materials that come in large sheets rather than many smaller shingles. 

Are flat roofs more prone to leaks than pitched roofs?

It is true that flat roofs are more prone to leak than sloped roofs. Because of their low slopes, flat roofs don’t drain as well as pitched roofs. This can lead to standing water causing leaks. 

Can you put a new flat roof over an old one?

It depends on the roofing material. A spray foam roof can be reapplied over an old roof. Some flat roofs can be overlaid with single-ply membranes. However, you cannot add overlays to metal roofs and green roofs; they will have to be torn off before a new roof can be installed. 

Before you decide whether to reroof or to replace your roof, consult a roofing contractor on what will work best for you and your roof.

Ready for a New Roof?

Flat roofs are a cost-effective, low-maintenance way to protect your home. While low-sloping roofs may not be the perfect roof for every building, they are a good, dependable option for many homeowners. 

Are you thinking about getting a new roof but flat out of ideas on where to start? Find a professional roofer near you to help you kick off your roofing project.

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Danielle Gorski

Danielle Gorski lives with her family in Texas. She has a degree in Professional Studies and a minor in marketing. Her hobbies include reading, drawing, and writing.