What Are The Different Layers Of A Flat Roof?
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What Are the Different Layers of a Flat Roof?

commercial building with multi-layered flat rooftop

You may not have ever noticed, but most residential roofs are steep-slope-styled roofs while commercial roofs are typically slow-slop or flat. These steep-slope roofs have a noticeable pitch or angle, while low-slope and flat roofs have a minimal pitch or are completely flat. 

Of course, flat roofing has become increasingly popular among homeowners, and for good reason.

Flat roofs tend to wear better compared to the traditional steep-slope style. However, they’re much more complex than you’d imagine. For starters, they have a surprising number of layers, and they’re not 100% flat. They also can cost a bit more than your traditional roofing system, depending on the size of your property. 

Want to learn more about the different layers of a flat roof and the materials used? Keep reading!

Why It’s Important to Have Multiple Layers of a Flat Roof

Each layer of a flat roof is providing an extra layer of protection, durability, etc. It is crucial to install these respective layers to build up the strength of a flat roof. The strength and accessibility of these roofing systems are a major draw for commercial properties that want to protect their businesses.

Flat roof systems usually include three elements:

  • A weatherproofing layer
  • A reinforcement layer
  • A surfacing layer

Each layer plays a very specific role in the integrity and longevity of a flat roofing system. 

Weather Proofing Layer

contractor waterproof flat commercial rooftop with bitumen layers

All flat roofs will have at least one weatherproofing layer, although you’ll find that many tend to have additional weather or waterproofing layer. This layer is designed to protect flat roofs by preventing moisture from seeping into the home or building.

When an additional layer is added, it’s typically to further protect the roof from ice and snow damage in areas that see a lot of this type of weather.

There are also different weatherproofing materials that can be used for flat roofs. This would include bituminous membranes and polyurethane liquid membranes.

Reinforcement Layer

The reinforcement layer is responsible for making flat roofs more durable by providing structural stability. For example, flat roofs using bitumen — a sticky, black layering material that comes from crude oil distillation — will typically have additional felt layers for reinforcement.

The reinforcement layers reduce the risk of the roof developing holes, cracks, or tears, which can later lead to leaks and other types of damage. 

Surfacing Layer

The surfacing layer is what protects the other flat roof layers from becoming damaged. For example, constant exposure to the sun’s UV rays or the other elements can quickly damage the lower layers if there isn’t adequate protection. 

While weatherproofing and reinforcement layers are designed to be more durable to withstand the elements, they benefit immensely from having that extra layer of protection on top. This surfacing layer also contributes to the longevity of flat roofs by preventing UV ray penetration.

What Are the Different Types of Flat Roofs?

Layers aside, there are a few different types of flat roofs that homeowners can choose from. Of course, the materials used will directly affect the cost, as will other factors, such as the location and size of the roof. 

Residential flat roofs also typically come with a 10 to 20-year warranty but can last up to 25 years or longer when installed and maintained properly.

These are some of your options, along with their pros and cons:

Built-Up Roof (BUR)

layers of a flat commercial roof newly installed

The built-up roof is the most traditional type of flat roof. It’s made from hot tar and gravel and waterproofing materials. These layers are alternated, starting with the waterproofing material and then layered with hot tar and ballasted with a layer of smooth river stone. 

BUR roofing was traditionally made from tar paper. Over time, however, they began gradually incorporating more advanced materials, including fiberglass membranes, for more durability.

✅ The Pros:

  • Gravel is a fire-retardant material, making it more protective
  • It’s aesthetically attractive, especially if you have windows and decks overlooking the roof
  • It’s the most affordable out of all the other flat roof options

❌ The Cons:

  • It’s very heavy
  • The joists usually need extra strengthening (which costs more time and money)
  • It’s messy to install and has a distinct odor
  • Installation isn’t usually recommended for occupied homes
  • Gravel that moves can end up clogging gutters and scuppers
  • It can be difficult to find the source of leaks if any occur

Modified Bitumen Roof

The modified bitumen is a single-ply rolled roof — much like an ice-and-water shield. Only, it’s enforced with a mineral-based wear surface. This type of flat roofing uses torch-down systems to heat the adhesive material as it is unrolled onto the roof. 

There are also newer peel-and-stick systems that are safer and easier to apply for the DIYer. However, the installation can still be tricky.

✅ The Pros:

  • You can install the peel-and-stick version yourself
  • The material is usually light in color to reflect UV rays and heat, which cuts down on your energy bill
  • It’s moderately priced

❌ The Cons:

  • Torch-down application is considered a fire hazard and therefore is not recommended for occupied homes
  • The material itself isn’t as scuff- or tear-resistant as other flat roofing materials, such as rubber membrane roofs

Rubber Membrane Roof

commercial building with protective edpm mebrane layers of a flat roof

Rubber membrane roofs are made from ethylene propylene diene monomer (EPDM). It’s a “true rubber” that comes in the form of a durable, single-ply membrane that resembles that of an inner tube. However, it’s designed to resist UV damage caused by sunlight.

EPDM can be mechanically installed via anchoring with fasteners, ballasted with stone, or glued. Your roofing contractor will recommend the best installment method for your property and location upon your roof’s initial assessment.

✅ The Pros:

  • Installation is DIY-friendly
  • The material itself is relatively light
  • The material is also incredibly durable and scuff- and tear-resistant
  • Leaks are easy to patch up

❌ The Cons:

  • The material costs more compared to the other options — especially if you opt for the lighter-colored coatings that won’t absorb heat (which are recommended in warmer climates)
  • It’s slightly more vulnerable to punctures and holes compared to your other options

Does Your Flat Roof Need Repairs?

Flat roofs are an excellent alternative to the traditional steep-slope style. The layers of a flat roof make them especially durable, allowing your roof to keep your home looking sharp for years to come. But no roof is invincible. Storm damage, a lack of roof maintenance, and every year that goes by can have an effect on the integrity of a roofing system.

For commercial roofing questions, repairs, & insight call Trust Roofing.

We are flat roofing specialists with a strong track record of installing the best and most reliable roofs. We pride ourselves in getting the job done right — the first time.

We have over 30 years of roofing experience, and we only use the best materials and equipment for the job!

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