Pros and Cons of Flat Roofs

A picture showing a house with flat roof

If you admire modern architecture, you might be drawn to homes with flat roofs. They not only stand out with their unique style, but they are generally more energy efficient than traditional pitched roofs. But before falling in love with the home of your dreams, consider the pros and cons of flat roofs.

What is a Flat Roof?

They’re pretty self-explanatory, right? Flat roofs are flat roofs. 

Close, but not exactly. A flat roof is technically any roof with a slope, or pitch, of 10 degrees or less — just enough of an incline for water to run off. If you think about it, an entirely flat roof will only accumulate rainwater rapidly and inevitably leak. 

Types of Flat Roofs

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

EPDM (ethylene propylene diene monomer): Synthetic rubber sheet material commonly used as a pond liner.

Built-up roofing (BUR): Bottom layer or two of insulation board, multiple intermediate layers of tar or asphalt alternated with layers of roofing felt, and a top layer of gravel

Modified bitumen roofing (MBR): Flexible, asphalt-based material with a mineral top coating that comes in rolled sheets 3 feet wide and up to 36 feet long; sheets are rolled onto the roof atop a base sheet membrane

Concrete: Made of sand, cement and water

Glass Reinforced Polyester (GRP): Durable, watertight fiberglass material

Metal: Metal sheets made of aluminum, copper, steel, or zinc

Green Roof: An eco-friendly rooftop garden made of plants and other lightweight greenery

Polyvinyl Chloride (PVC): Flexible thermoplastic waterproofing membrane made of vinyl

Spray Polyurethane Foam Roofing (SPF): Sprayable liquid foam that dries and hardens

Thermoplastic Polyolefin (TPO): Large, lightweight, flexible sheets made of two types of rubber

Pros of a Flat Roof

There are many benefits to flat roofing.

Versatile, Usable Space

A picture showing a flat roof at top
Photo Credit: Tomisti / Wikimedia Commons / CC BY-SA 3.0

Flat roofs open up a variety of opportunities for recreation and relaxation, such as sunbathing and gardening. You can convert your plain flat roof into part of your living space.

Roof Deck/Terrace

A flat roof enables you to enjoy warm weather with all the advantages of a regular deck but with an expansive view. You’ll need to have a roofing professional evaluate your flat roof to ensure it’s structurally sound enough to withstand foot traffic. If it’s not, a contractor must fortify it. You’ll also need to get any local permits required or HOA approval before transforming your roof into a terrace.

Swimming Pool

If a roofing professional says that your flat roof can withstand a rooftop pool, you’ve got an excellent way to keep cool during the summer without using yard space. A hot tub may be an excellent alternative if the pool is too much or the space is too small.

Rooftop Garden

A garden installed at top of a roof
Photo Credit: Debbiehelbing / Canva Pro / License

A flat roof is an easy solution for those with green thumbs who could always use the extra gardening room. Whether you’re growing vegetables or flowers, a green roof is advantageous because it gets more sunlight and is less likely to be infested by weeds or pests. If you’ve ever wanted to try your hand at beekeeping, a rooftop garden is the perfect place to incorporate bee hives.

Solar Panels

Solar panel installed on a top of a roof
Photo Credit: Sean2008 / Canva Pro / License

If you’ve thought about being more eco-friendly while saving money on your energy bills, a flat roof is the perfect place to install solar panels. Depending on the location of your property, a pitched roof might not have the best angle to catch the sun’s rays; a flat roof means your panels can easily be installed to face the sun in almost any direction.

Easy to Repair

Depending on the scale of damages on your flat roof, repairs are often easier to make than on  a sloped roof. The flat surface is less dangerous to walk on and easier to maneuver equipment. It makes it easier for a DIYer to make simple repairs.

Affordable Cost

The cost to install a flat roof ranges from $4,300 to $19,100

Flat roofs are cost-effective in several ways.

  • Materials: Not only are flat roofing materials less expensive than pitched roof materials like metal, clay, and slate, but you also need far less materials than with a pitched roof.
  • Labor: Hiring a professional for roof installation costs less because there’s less risk involved, and the installation process is more straightforward and quicker. 
  • Repairs: Repairing a flat roof is safer and easier, saving you money on repair costs. The average range for flat roof repairs is $300 to $1,175.

Good Temperature Regulation

If your flat roof is well insulated, you’ll be able to better control the temperature in your home. Because there’s no pitched roof or attic space in which hot air can get trapped, your HVAC and heating systems work less to maintain equilibrium in your home. EPDM roofing in particular can help retain heat to lower heating bills, while other types of flat membrane roofing can reflect it to keep your home cooler. 

Flat roofs also have better energy efficiency because of their membrane systems, which are applied on top of rigid insulation sheets. Pitched roofs use a cavity insulation system which has gaps in it. Because flat roofs have no such gaps, the insulation is continuous and therefore saves energy.

Easy to Clean

A picture showing a flat gravel roof which is easy to clean
Photo Credit: Kenny10 / Canva Pro / License

Cleaning a flat roof is much easier than cleaning a sloped one. Use a broom, leaf blower, or mop and soapy water to keep it looking pristine. There’s also the extra advantage of being able to clean your gutters and reach your home’s siding more easily from a flat roof.

Cons of a Flat Roof

The benefits of a flat roof are great, but you may decide to go with another roofing option if you don’t want to deal with the drawbacks. 

No Loft or Attic Space

Without a pitched roof, you won’t have the benefit of attic storage space. While no attic may make it easier to regulate temperatures, you’ll have to rely on closets or possibly rent a storage unit if you have a lot of stuff you need to store. Alternatively, some homeowners convert their attic space into a loft or extra bedroom, which isn’t an option with a flat roof. 

Harder to Drain

Flat roofs don’t drain as well as pitched roofs because of the minimal incline. Many flat roofs require membrane systems, which is a roof covering installed on top of the roof that lets water drain. Your roofing professional also may install special drainage systems to route water to make sure water is properly draining.

Rain and Snow Buildup

Snow piled up on a flat roof
Photo Credit: Pexels

Rain and snow are rough on a flat roof. There are several ways snow and ice accumulation, in particular, can cause damage to your roof. 

  • Bowing: The more snow accumulates on your roof, the more unwanted weight applies pressure onto it. Over time the weight and gravity will cause the roof to bow downward, losing its flatness and paving the way for further damage.
  • Ponding: Melted snow or rain which forms large puddles on your flat roof is called ponding, and it harms the integrity of the roof materials. It also can interfere with any electrical systems on the roof. 
  • Freeze-Thaw Cycles: Often rainfall or melted snow will freeze after ponding, and when water freezes, it expands. The water can fill cracks, and when the water freezes, it widens the cracks even more. If left unaddressed, the damage will grow and eventually lead to a leaky roof.
  • Leaks: As the flat roof gradually weakens from bowing and ponding, holes will eventually develop in the roof, leading to leaks. You may be able to repair these yourself if they are minor enough; otherwise you’ll have to contact a roofing company. 

Shorter Lifespan

Flat roofs may cost less to install, but they likely won’t last as long as a pitched roof. A well-maintained flat roof can last 10 to 20 years, while a pitched roof can last 20 years or more, depending on the materials.

FAQ about the Pros and Cons of Flat Roofs

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. 

How Do I Extend the Lifespan of my Flat Roof?

Proper roof maintenance is the only way to extend the lifespan of your flat roofing system. This includes regular inspections from a professional roofing company. Expect to spend between $120 to $320 for a thorough examination of all your flat roof elements and a written report detailing any findings. 

What is the Best Climate to Have a Flat Roof?

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 like the Southwest, and not areas where it gets a lot of moisture, snow, ice, and freezing temperatures.

Is a Flat Roof for You?

Flat roofs offer a lot of benefits, like energy efficiency and lower cost to install and repair. But they do cut down on storage space and can have drainage issues. While flat roofs may not be the perfect roof for everyone, they are a good, dependable option for many homeowners. 

If you think a flat roof is for you, hire a professional roofer near you to help you with your roofing project. 

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Zach Bridgeman

Zach Bridgeman

Zachery Bridgeman is a writer who grew up in Alabama and currently lives in Pittsburgh, PA. He enjoys writing fiction, painting, and exploring the city in his free time.