Flat Roof Pros and Cons

Are you a potential homeowner who’s considering a flat roof for your new house? Or are you a homeowner planning to give your home a fresh look with a flat roof?

If you said yes to any of these questions, having the right information about flat roofs is essential to help you make an informed choice. Understanding the benefits and drawbacks of flat roofs not only saves you time and money but also helps you determine if it’s the right fit for your home.

What is a Flat Roof?

a house with a flat roof

A flat roof is a nearly level roof that sits parallel to the ceiling joints. It stands out compared to pitched ones. It’s not actually flat – it has a very gentle slope, around 1/4 to 1/2 inch per foot, to ensure water drains off. The typical slope is no more than 10-15° to the horizontal. You’ll often find this type of roof on commercial buildings or small structures like extensions, garages, and carports. It’s also covered by a waterproof layer

Modern materials and designs have updated flat roofs. While commercial buildings and skyscrapers often use them, more homeowners are considering flat roofs as an alternative to traditional pitched designs. It’s getting common in contemporary houses, where homeowners seek a modern aesthetic, and the climate isn’t heavy on rainfall or snow.

Advantages of a Flat Roof

Lower upfront cost

Flat roofs often bring better cost efficiency compared to pitched roofs. The steepness of a roof, known as its pitch, significantly affects the price due to the increased complexity of construction for steeper roofs. Flat roofs, with their gentle slope, need less material.

When it comes to your budget, flat roofing systems take the prize for cost-effectiveness. Choosing a pitched roof over a flat one for the same area can cost you thousands of dollars more. To put it into perspective, a 900-square-foot single-ply flat roof might set you back around $7,000, while a pitched roof of the same size could reach $9,000 or beyond. If saving money upfront is on your agenda, a flat roof is the savvy choice.

These roofs are also a budget-friendly option for extensions. So, if you’re thinking of adding a conservatory or an extra room to the upper floor of your home down the line, a flat roof won’t hit your wallet as hard as a pitched roof extension would. Besides their easier installation, the repair costs of pitched roof extensions make them pricier than flat roofs.

Energy-efficient

Flat roofs also have an edge in energy efficiency compared to pitched roofs. This is thanks to the insulation used. Pitched roofs often rely on fiberglass insulation, which may be less effective than the spray foam insulation often found in flat roofs. Spray foam insulation creates a seal around your home, keeping warmth indoors during winter and ensuring a cooler home in summer. This can lead to significant energy bill savings. In warmer climates with prolonged sun exposure, an energy-efficient white-colored roof membrane can even help homeowners recoup thousands of dollars in energy savings.

Built to last

Modern flat roofs have high-performance membranes designed to endure even the harshest weather conditions. One such material is EPDM, a rubber-based substance that’s eco-friendly. This roofing is not only waterproof but also fire-resistant and wind-resistant, capable of staying strong for up to 50 years.

With this durability, you can rest easy knowing your flat roof can withstand storms, temperature fluctuations, and heavy rainfall. Another strong option is modified bitumen, introduced in the 1960s, which features reinforced polymer sheets for added toughness. Unlike delicate roofing materials like clay or tiles that can crack or break, a flat roof remains resilient year after year.

Safer and more accessible to maintain

Flat roofs also shine in terms of safety and accessibility compared to pitched roofs. With steeper pitched roofs, reaching the roof requires more equipment and carries a higher risk of injury. On a flat roof, walking is easier, and fewer tools are needed for maintenance. You can simply walk up to your roof to check for any issues. This makes it a safer option for homeowners who aren’t experienced in navigating pitched roofs, reducing the risk of accidents. This not only makes routine upkeep safer for homeowners, but it also reduces the cost of roof servicing.

Provides usable outdoor space

Another fantastic perk of flat roofs is their potential to provide usable outdoor rooftop areas, which can be a cool hang-out space for your family. If your home doesn’t offer much square footage, a flat roof can become an excellent spot to craft a rooftop deck, a charming garden, or a house with an entertaining zone with a hot tub. This extra space outdoors is perfect for social gatherings, leisure time, or even as a home office space. While commercial buildings often utilize flat roofs to discreetly house HVAC systems and equipment, the possibilities for this extra space are boundless and can cater to your needs and ideas.

Aesthetically-pleasing

Don’t be fooled into thinking that flat roofs are dull and uninspiring. Quite the contrary, many homeowners discover that flat roofs can possess considerable aesthetic charm. With the right design approach, a flat roof can infuse a modern flair into your home’s exterior. Plus, their streamlined nature, with fewer angles and eaves, offers the opportunity for more expansive windows and breathtaking views.

For instance, a rooftop garden can add a touch of elegance and glamour to your home. The beauty of opting for this roofing style lies in its versatility to complement various landscaping themes, particularly contemporary designs. There are many captivating designs that can spark your inspiration.

Allows for easy compliance with height limits

Certain states or communities impose height limits on residential structures, especially multi-family buildings. A flat roof’s construction lends itself well to adhering strictly to these regulations. This advantage might not be as attainable with pitched roofs, particularly for larger structures.

Provides practical outdoor storage

In search of a practical storage solution for items like ladders, solar panels, HVAC units, or a satellite dish? A flat roof serves as a secure and discreet option for installing these items, seamlessly integrating them without marring the visual appeal of a pitched roof. Vandalism, tree contact, and proximity to other appliances are going to be less of a concern. However, it’s crucial for roofing contractors to assess the roof’s substructure to ensure its capacity for holding the units. Improper installation can lead to low spots and leaks.

Seamless solar panel integration

When comparing flat roofs to pitched ones, the former provides the ideal canvas for installing solar panels. Placing these eco-friendly and energy-efficient solutions on a flat roof enables optimal panel angles and maximizes their effectiveness, giving you the best return on your investment.

Perfect for future home extensions

Should you have plans for expanding your home down the line, a flat roof is the roofing choice to consider. Their simplicity translates to swift project completion during home extension endeavors.

Drawbacks of Flat Roofs

Comes with challenges in drainage

Among the significant drawbacks of flat roofs is their drainage, or lack thereof. While they do possess a slight slope for water runoff, it’s not nearly as effective as the steep pitch of a traditional roof. Rainwater often accumulates on the roof, forming puddles that can lead to leaks or material deterioration.

To counter this, prioritize top-quality felts during flat roof installation, even if they come at a slightly higher cost. This investment ensures the longevity of your roof. Hiring a reputable roofing company to install your flat roof – they will be able to establish a comprehensive maintenance plan, conduct routine inspections, and provide warranties for both materials and services.

Aesthetic limitations

If aesthetic appeal is your priority, flat roofing systems might not offer much variety. They often come in basic colors like black, white, or grey – unlike pitched roofs that can be available in other vibrant colors like red, blue, and green. Fortunately, it isn’t visible from the ground. What can make a flat roof beautiful depends on what you put up there, like a rooftop garden or a welcoming lounge area.

Needs more maintenance

One major drawback of flat roofs is their higher maintenance and upkeep demands compared to pitched roofs. Due to their design, flat roofs are more vulnerable to damage. While not perfectly flat, they can still encounter drainage issues leading to leaks. Even seemingly minor factors like bird droppings require consistent removal to prevent roofing material degradation. This is a concern across all roof types, but flat roofs, offering more space for birds, magnify the issue.

The solution lies in proactive biannual inspections—preferably in spring and autumn. Clean your roof more frequently during these seasons, and especially after storms. Prevention is better than cure. Clear debris and leaves obstructing proper drainage, and promptly seek repairs post storms. If needed, engage a structural surveyor for a thorough roof assessment.

Limited material choices

Options for flat roof materials are restricted, with availability often limited. Selections include Asphalt, CPE, CSPE, EPDM, polyolefin, rubber, TPO, modified bitumen, and thermoplastic. The availability hinges on the chosen material type and local accessibility.

Shorter lifespan

Flat roofs, due to their susceptibility to damage, possess a shorter lifespan than pitched roofs. While it’s built to last, flat roofs endure 10-20 years on average, in contrast to pitched roofs that can last 30-50 years or more. The presence of errors from inexperienced roofing companies can lead to this disparity. Expect the need for more frequent flat roof replacements, entailing a substantial financial commitment.

For improved longevity, consider alternatives like polyurethane liquid, GRP fiberglass, or polycarbonate roofing, often coupled with EPDM rolled rubber. Although slightly pricier, these materials offer potential longevity enhancements. EPDM rubber roofing, notably, can withstand up to 50 years if not punctured.

Temperature variation

Flat roofs tend to absorb heat more readily than pitched roofs. Their constant exposure to sunlight throughout the day contributes to this phenomenon. During hot months, your home can become uncomfortably warm, while winter might bring a chill. However, this concern lessens if the flat roof adorns a garage or shed, as these spaces aren’t frequented for extended periods.

Poses challenges on bigger structures

While flat roofs suit small homes well, they may exhibit less stability on larger buildings. Weight distribution issues arise due to the size, potentially causing sagging or collapse if inadequate support is provided. Commercial structures counter this by implementing robust support systems to evenly distribute the roof’s weight.

Lack of attic space

A flat roof often eliminates the presence of an attic, necessitating alternative storage for seasonal items like holiday decorations. While a minor inconvenience for some, this can pose significant storage challenges for others, particularly if alternative storage areas are limited.

Plant growth concerns

Green roofs may introduce a plant intrusion risk, particularly with plants boasting invasive roots. Invasive roots have the potential to infiltrate the roof structure, causing detrimental leaks over time.

Debris buildup and maintenance

In addition to water accumulation, flat roofs can collect dirt, leaves, twigs, and debris that hinder proper drainage. Regular inspections and maintenance are crucial to preserve the roof’s longevity and functionality.

Higher insurance costs

Due to the heightened risk of leaks, flat roofs often incur higher insurance premiums. This contrasts with pitched roofs made from durable materials like aluminum or zinc, designed to withstand various elements and efficiently drain water and snow.

Pros and Cons of the Different Types of Flat Roofs

There are different ways and various materials to install flat roofs, and each is unique. Because of that, each of them poses an advantage and disadvantage. Get to know the different types of flat roofs below:

Built-Up Roofing (BUR)

built-up roofing on a flat roof with fencing

Built-up roofing (BUR) is the original method used for flat roofs, and it’s still quite popular. It was the standard flat roof before newer options like modified bitumen and membrane roofing came along. BUR is made up of layers: an insulation board at the bottom, alternating layers of tar or asphalt and roofing felt in the middle, and a top layer. This material uses layers of asphalt applied between roofing felt sheets to build up the roof. Then, a protective layer—usually gravel or stone—is placed on top. This upper layer safeguards the lower ones from UV damage and falling debris impact.

These roofs consist of layers about three feet wide, covered in hot melted tar. During installation, professionals melt coal pitch or asphalt tar in a large kettle and then spread it on the roof. After adding two to four layers, they use gravel or small stones to shield the roof from UV rays. With proper care, these roofs can endure for 15 to 30 years.

While BUR flat roofs are cost-effective and fire-resistant, they do take longer to install due to their complexity. They require professional installation and can be heavy due to the numerous layers involved.

Pros:

  • BUR excels at guarding against water, UV rays, and harsh weather.
  • It’s low-maintenance and requires minimal upkeep over its lifespan.
  • Layers can be easily removed during repairs or resurfacing.
  • The gravel layer in BUR handles regular foot traffic really well.

Cons:

  • Installing BUR is slow and labor-intensive due to the multiple layers and materials.
  • The installation process can produce potentially hazardous fumes and vapors.
  • The roof assembly is heavy, sometimes needing stronger roof joists for support.
  • Tracking down a leak can be tricky and might involve disassembling the entire roof.
  • Built-up roofing can become brittle in cold temperatures, making it more prone to damage.

Modified Bitumen Systems (MBS)

Worker preparing part of bitumen roofing felt roll for melting by gas heater torch flame

In the 1960s, modified bitumen systems (MBS) emerged as an alternative to traditional BUR flat roofs, and they’ve gained popularity ever since. For this type of flat roof, a layer of asphalt blended with polymers is applied to the roof structure and reinforced with fiberglass or polyester. To enhance weather resistance, a base coat and top coat are added on top of these layers. They’re thicker than single-layer membrane roofs, making them better equipped to handle heavy foot traffic if used as an outdoor space.

Compared to BUR flat roofs, MBS flat roofs are quicker to install thanks to their convenient roll sheets. It’s a flexible, asphalt-based material with a mineral top coating, similar to regular asphalt shingles. Available in rolled sheets about 3 feet wide and up to 36 feet long, these sheets are rolled out onto the roof over a base sheet membrane.

A modified bitumen roofing system can endure for 12 to 20 years. Installation options include:

  • Applying hot layers with hot tar.
  • Using cold adhesive solvent without heat.
  • Torch-down installation, melting both sheets together with a flame.
  • Peeling and sticking both sheets after removing the release tape. The top cap sheet is granulated and comes in a light color.

However, they might be more susceptible to water pooling compared to single-layer membranes, and their seams might not handle standing water, as well as flat roofs with thermoplastic membranes like PVC.

Pros:

  • Factory-applied mineral surfacing ensures consistent installation.
  • Installation is much simpler compared to BUR, reducing labor and errors.
  • Offers better flexibility in colder temperatures compared to BUR.
  • MBR is low-maintenance and durable.
  • Homeowners can install self-adhesive roll roofing.
  • Most MBR material is recyclable, like asphalt shingles.
  • Balances durability and installation ease, similar to EPDM.

Cons:

  • Some application methods involve open flames or torches, requiring special skills and safety measures.
  • Properly adhering to overlapping joints is crucial to avoid leaks.
  • Modified bitumen might not be as visually appealing as BUR or membrane roofs with gravel or river rock.

Membrane (Single-Ply) Roofing

A newer contender in the world of flat roofing is single-layer membrane roofing. It involves applying a single membrane over the building’s underlying roof structure. The go-to material for this kind of flat roof in modern construction is Ethylene Propylene Diene Monomer (EPDM), which is a sturdy synthetic rubber. But don’t forget about alternatives like neoprene, PVC, and polymer-modified bitumen.

Membrane roofing involves putting an insulation board under layers (the membrane) of EPDM rubber or other materials. This EPDM layer can be laid loosely and secured with ballast like river rock or masonry pavers. Alternatively, it can be fastened or glued to the insulation layer.

Since these membranes are made of rubber or polymer, they handle temperature changes well and stand up to wear and tear. Additionally, this type of flat roof is lightweight and relatively quick to install, which is good news for DIY enthusiasts. However, keep in mind that single-layer membrane roofs tend to be pricier than other options and might be more prone to wear and tear.

Pros:

  • Repairs are usually straightforward and affordable; homeowners might be able to handle some fixes themselves.
  • There is no need to reinforce the roof deck because EPDM roofing is lightweight.
  • Leaks are rare with EPDM roofing as long as there’s no surface damage.
  • EPDM roofing can hold heat to lower heating costs, while other membrane options can reflect heat to keep the home cool.

Cons:

  • Installing around roof penetrations (like pipes, HVAC systems, and chimneys) is more complex and costly; if not properly flashed, these areas can lead to leaks.
  • Falling branches, foot traffic during installation or maintenance, or storm damage can puncture membranes and cause leaks.
  • Seams between membrane sheets, even though they’re sealed, are common spots for leaks.