Everything You Must Know About Flat Roofs (Pros and Cons)

what you should know about flat roofs

There are many roof design options, but most designs consist of one or more pitched surfaces to create the roof. Flat roofs are unique in that they have a surface with minimal slope, which presents a particular set of advantages and disadvantages.

Flat roofs offer many benefits, including lower construction costs, easy maintenance, excellent durability, and the creation of a versatile roof space you can use for various purposes. The often undesirable appearance of a flat roof and the design's difficulty with water drainage are some downsides.

Whether you're building from scratch or looking to purchase a home with an existing flat roof, it's essential to know the ins and outs of the design before you commit to the decision. Below let's take an in-depth look at the many advantages and disadvantages of having a flat roof.

Flat Roof Advantages

Many people prefer flat roofs over traditional gable roofs or other sloping designs, for a good reason. There is a lot to like when it comes to flat roofs. Let's dive right in and take a closer look at the various benefits you can expect from a flat roof.

1. Lower Construction Costs
While the exact cost of a flat roof depends heavily on the materials you choose, labor prices, and many other variable expenses, generally, you can expect to pay less than a traditional pitched roof. The average roof replacement cost is $8,786, while the average cost to replace a flat roof is only $6,659.

There are many reasons why a flat roof costs less. First, flat roofs typically require less material than a roof with a more extreme slope because there is simply less surface area. A smaller surface area on the roof means that you need fewer materials and can generally complete the project in less time.

Roofs with a more extreme pitch can require roofers to wear harnesses and other complex safety equipment during construction, while flat roofs are much safer and more accessible. Constructing a flat roof can help save time and money because of the ultra-accessible nature of the design.

2. Wide Selection of Roofing Materials
Many homeowners have the misconception that all flat roofs are the same and often appear quite bland. However, this is far from the truth. Much like materials for traditional pitched roofs, there is a wide selection of roofing materials to choose from when constructing a flat roof.

With so many flat roofing materials to choose from, you can compare the different options to find the best fit for your particular situation. There are so many types of flat roofs you're sure to find one to fit all your needs and preferences perfectly. Below are a few of the best and most popular materials used for flat roofs:

  • Built-Up - The built-up flat roof style consists of asphalt and felt layers that are applied on top of each other to create an efficient and long-lasting roof surface.
  • Modified Bitumen - Modified bitumen is a flat roofing material consisting of multiple layers, including an asphalt base coat, rubber or fiberglass reinforced layer, and a durable cap sheet.
  • Thermoplastic Membrane - Single-ply thermoplastic membrane flat roofs often attach to the roof deck using screws and provide an efficient and durable roofing surface. There are two categories of thermoplastic membrane roofing materials: TPO and PVC.
  • Rubber Membrane - Rubber membrane roofs, called EPDM roofs, are single-ply and can attach to the roof deck using an adhesive or held in place using a layer of rocks on top of the rubber.

Additionally, there are other flat roof materials available such as spray-on, concrete, metal, and more, but they are generally less common. All of that to say, there are a ton of options when building a flat roof, so you should have no trouble finding a material that fits your needs, preferences, and budget.

3. Easy Maintenance and Repairs
Compared to more steeply pitched roofs, flat roofs are exceptionally accessible, and you can walk on them without much trouble. Their accessibility makes flat roofs easy and affordable to maintain and repair.

Because flat roofs are so accessible and provide a relatively level surface to stand on, homeowners can easily perform most maintenance, inspection, and cleaning needs. You don't have to deal with a sloped surface and all of the accompanying safety equipment you need to climb on a steeply pitched roof when you have a flat roof.

Additionally, once you've identified any cracks or imperfections in your flat roof, repairs are often straightforward to perform on your own. You can simply purchase patches for most flat roofing materials to seal the affected area.

4. Excellent Durability
Flat roofs are a sturdy and durable roofing option that can withstand most environmental influences that impact a typical home. The membrane construction of most flat roofs also creates a cohesive water barrier with few possible leaks. And if your flat roof sustains damage, you can generally repair most flat roof materials by applying a patch to the affected area.

The precise durability of a flat roof largely depends on the material you use to construct the surface and the climate where you live. Because there is such a wide selection of roofing materials on the market, the expected lifespan of a flat roof can vary widely.

Here are some of the most common flat roof types and their expected lifespans:

Flat Roofing TypeExpected Lifespan
Built-Up15-30 years
Modified Bitumen15-20 years
Thermoplastic Membrane20-30 years
Rubber Membrane35-50 years

5. Creates a Versatile Space
Most roof designs make the roof surface nearly unusable due to its extreme slope. On the other hand, flat roofs can create a versatile and useful space that is essentially an additional open-air level to your home.

You can use the roof space for purely practical purposes, such as holding an AC unit, or make the area into an outdoor deck. Rooftop garden "green roofs" are extremely popular and great for utilizing the space. You can also create an outdoor barbecue area, hang laundry, or install solar panels—the possibilities are nearly endless.

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Flat Roof Disadvantages

As with most things, there are some disadvantages to flat roofs that you must consider when deciding if the design is right for your home or not. It's better to make a well-informed decision by knowing the good and the bad than to be surprised later.

1. Suffers Water Drainage Issues
Flat roofs are extremely flat compared to other more steeply sloped roofs, but they do have a slight pitch. A completely flat roof is never a good idea as it wouldn't allow rainwater or snowmelt to run off the roof and would end up causing lots of damage.

Roof pitch is usually given by two numbers separated by a colon. The second number is nearly always 12 to indicate a foot, and the first number shows how many inches the roof rises every foot. Most flat roofs have a pitch between ¼:12 and 2:12, roughly equal to 1 to 10 degrees.

The slight pitch that a flat roof has allows rainwater to more efficiently flow off of the surface, but the placement of drains is arguably even more important. Flat roofs typically suffer from lackluster water drainage, so it's important to make it a priority when designing and building your roof.

2. Easily Collects Dirt and Debris
Traditional steeply pitched roofs often do not run into this problem, but flat roofs can easily collect dirt and debris. Flat roofs not only provide a nearly level surface for debris to collect, but many designs include a raised edge around the roof's perimeter that exacerbates the problem.

Debris and dirt collection on your flat roof is very unsightly, but it has more serious implications that you must also consider. Debris can easily scratch the roof's surface or build up and trap moisture. Both of these problems can damage your roof's surface and cause water leaks or shorten your roof's expected lifespan.

3. Provides Little to No Attic Space
Most steeply pitched designs, such as gable or hip roofs, leave lots of internal attic space underneath the structure's top. Flat roofs, however, leave little to no attic space. Depending on the climate and situation, a lack of attic space can be not a problem or a major hurdle to overcome depending on your situation.

Many homeowners primarily use their house's attic area as additional storage, but the space serves a second more important function: it helps to regulate the home's temperature. The attic holds insulation and acts as a slow-moving air buffer between the roof and the indoors.

A flat roof can be a great option if you can go without the additional storage space, and compact modern insulation material is enough to insulate your home properly. You can insulate a flat roof well and make it extremely energy efficient, but the lack of attic space can be a potential downside that you should keep in mind.

4. Undesirable Appearance
Last but not least when it comes to the downsides associated with flat roofs is the style's appearance. People tend to be split regarding the look of a flat roof, with many liking the industrial feel while others think it's plain ugly.

It's also essential to consider your local laws and regulations regarding the types of roof designs you can have on your home. Many residentially zoned areas have strict rules regarding the type of roof you can have on your home, so make sure it's allowed in your neighborhood before moving forward with the project.

Is a Flat Roof a Good Option for Your Home?

Flat roofs have their fair share of potential downsides, but none immediately disqualify the design. There are many great benefits to having a flat roof that make it a great option for many people, but it's important to establish if it is the correct design for you and your home.

There are tons of great advantages to having a flat roof, ranging from lower initial costs and easy maintenance to excellent energy efficiency and a wide selection of material options. Not to mention a flat roof creates a functional and versatile space on the roof of your home that you can use in various ways.

While there's a ton to like about flat roofs, there are also many important downsides to consider. Below are three of the most significant reasons that indicate a flat roof is not the best design option for your project:

  • Undesirable or Unallowed Design - Flat roofs have a very industrial look to them that many people have strong opinions on. If you don't like the look of a flat roof or your area forbids the design, it's best to avoid the hassle and consider other roof designs that better fit your preferences and laws.
  • Lots of Rain - There's no denying that flat roofs are not the most efficient at allowing rainwater to run off your home. If you live in an area that receives lots of rainfall, it's best to go with a roof with a steeper pitch. You'll avoid lots of headaches and expenses down the line by choosing a roof that is more conducive to the amount of rainfall your home receives.
  • Extreme Temperature Changes - Flat roofs do not leave much internal attic space or room for insulation due to their design. While you can insulate flat roofs incredibly efficiently, there are often better designs for regions that experience extreme temperature changes throughout the year.

By no means are the above reasons for not getting a flat roof definitive. There are exceptions and many more scenarios that are not ideal for a flat roof design. Flat roofs have numerous pros and cons, so it's important to carefully compare them to your situation to see if the design would be a good fit.

Whether a flat roof is the correct design decision for your home depends on the climate you live in and your personal preferences. It's important to carefully consider the design's pros and cons before making a final decision.

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