Types of Flat Roof Systems: Pros and Cons

Flat roofs usually don’t stand out in Florida like a classic clay tile roof, but they’re everywhere. You might associate them with big-box stores and industrial buildings, and for good reason. They offer a host of advantages in those applications. They also offer some solid advantages for residential use, which is why you often see them used on stylish modern homes, and on architect-designed homes. There are several types of flat roofs, too, all with their own pros and cons. So let’s look at types of flat roof systems: pros and cons.

Types of Flat Roof Systems

The main types you’ll see are:

  • Built-up roofing
  • Modified-bitumen roofing
  • Membrane roofing

Major Advantages of Flat Roof Systems

In general, flat roof systems provide one major advantage over pitched roof systems: more space for solar panels and other equipment. On a big-box store or industrial building, this is a big deal, as a 4/12 gable roof as you’d find on a typical home would be a massive affair on a 50,000 square-foot structure. A flat roof provides plenty of space for air-conditioning equipment, typically. And for residential use, flat roofs provide all kinds of room for solar panel. Plus, you don’t have to worry that the roof is pitched in the wrong direction. And now that solar panels have gotten so much cheaper, and you can get a 30% tax credit thanks to the Inflation Reduction Act, many people can put their roofs to work with solar panels making free electricity.

When we compare flat roof systems against pitched-roof systems, they hold their own for the most part. It’s sort of an apples-to-oranges comparison, though, between a membrane roof and slate tiles, for example. Slate tiles are a premium roofing material that should last for more than 100 years (except for hurricanes). No flat roof system can even come close to that, but they can still be a good value, so let’s look at the options.

Built-Up Roofing (BUR)

built-up roofing
Built-up roofing uses layers of asphalt sheets and hot tar.

This method is old-school and goes back decades. Your roofing crew will lay down alternating layers of hot tar and then asphalt-soaked roofing felt. This “sandwich” creates a waterproof barrier, and then the crew tops it all with a layer of gravel so you can walk on it.

Pros of this type of roof include relatively good waterproofness, UV protection, and fire resistance. Cons include weight; this type of roof is very heavy with all those layers. They also tend to be expensive, as they’re labor intensive. It’s hard to track down leaks, as water can travel between layers from one section of roof to another. Plus, it’s a slow and smelly process and usually not the best choice.

Modified-Bitumen Roofing

Modified-bitumen roofs are often called “torch-down” roofs.

Developed in the 1970s as a way to update the BUR system, modified bitumen roofing provides some key advantages over a BUR. They go on faster, for one thing. This method uses aphalt-soaked sheets of fiberglass or polyester that’s typically applied with a torch to melt the sheets together and make them watertight. That’s why it’s called a “torch-down” roof. That process presents some fire risk, so you want a top-notch crew doing this work. Instead of a gravel top coating, a modified-bitumen roof gets a cap sheet that’s much lighter and also works as a UV shield. Cons include a relatively short lifespan of just 10–20 years at a cost of about $750–$1350 per square including installation.

Membrane Roofs

Membrane roofs have a lot to offer compared to asphalt-based roofs. You’ll have three basic options to consider. These single-ply membranes go on pretty quickly, in contrast to a built-up roof and all of its layers and the labor of pushing hot asphalt around. Membranes are also light in weight and when used over rigid insulation, provide very good energy efficiency.

EPDM Roofs

EPDM membranes have been around for several decades and compare favorably to a modified-bitumen roof. With a solid installation job, an EPDM roof should last 20 years and cost from $400–800 per square. That also is comparable to asphalt shingles in Florida, by the way, so there is some solid value in an EPDM roof.

The cons with EPDM are the seams and penetrations. EPDM requires adhesive at the seams and penetrations around skylights, roof vents, plumbing penetrations, and so on. Over time those seams and penetrations will need maintenance. It’s wise to put a yearly roof check-up on your calendar.

TPO Roofs

The main advantage of TPO over EPDM is heat-welding of seams and penetrations. This method is considered permanent, while adhesive bonding as used with EPDM requires maintenance and touchups. In other respects, the two membrane materials are quite similar, so TPO is also superior in most respects to asphalt-based roofs. TPO can have a slightly higher cost than EPDM at $450 per square and up, but you really have to get a quote for your situation. A TPO membrane can either be fully adhered to the roof decking or attached with fasteners, depending on the circumstances and your roofer’s preferences. TPO is also fully recyclable a the end of its lifespan. Cons for TPO are is relative newness on the market. It just hasn’t been around as long as EPDM and PVC. But big manufacturers like GAF make TPO and stand behind their products.

PVC Roofing

PVC is available in large rolls and different thicknesses. Its white color reflects solar radiation.

PVC membranes have been on the market for more than 50 years and are still considered to be a solid choice, and possibly the best choice for a membrane roof. Like TPO, your crew will heat-weld the seams and at all penetrations. PVC is also considered to be incredibly strong, which is why it has been used in commercial and industrial applications so much. All that comes with the highest price for a membrane roof at $850 per square and up. But your price will depend on your roof and your contractor, so it’s best not to prejudge. Go ahead and get three quotes to compare.

We’re Here To Help With Flat Roof Systems

We know it can be confusing to look at your flat roof option and know what to choose. But we’re here to help. Whenever you’re ready, give us a call at 813-373-9088. Our team has more than 40 years of experience in roofing. You can also use this form and ask us, “Let’s talk about flat roof systems” and we will contact you.

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