Flat roofs are never a one-type-fits-all solution, which is why there are many different types of flat roofs. Knowing what type of flat roof your commercial or industrial building has makes a difference in what to expect for repairs and what to expect out of your roof’s lifespan. Different flat roof types have different payoffs, depending on what your building needs. If you’ve never installed or repaired the roof on your building before, here is a rundown of several common flat roof styles and how you can tell them apart.

Metal Roofs

If you have a metal flat roof, you’ll likely be able to tell very easily. The metal surface, if not painted, should be able to be easily seen, and it is likely patterned with indentions every several inches to a foot. They are most commonly made of steel or aluminum. Metal roofs, which are technically low-sloped roofs, are still installed today, but are decreasing in popularity as other commercial and industrial roofing options have become available in recent years.

A benefit to metal roofs is that they tend to have a higher up-front costs but a longer lifespan. On the other hand, metal roofing is a very permanent option, which makes it difficult to replace; in most cases, the old roof will need to be torn off completely in order to install the new one, whereas other flat roofing styles offer the option to be able to install a new layer of roofing on top of the old one. All roofs, no matter the type, will sustain damage at some point, and with metal roofing, rusting is the biggest risk. If your roof rusts, its strength will be compromised and it may develop holes unless the damage is taken care of.

Polyurethane Spray Foam Coatings

Polyurethane spray foam roofs (also known as SPF) are topped with a top coat designed to seamlessly waterproof your roof. If your roof appears reflective white or gray in color and has what looks like a sprayed-on pattern, you likely have a polyurethane flat roof. In the installation of SPF, base layers of dense polyurethane foam are sprayed onto the surface of the roof with a sprayer or wand. After this is complete, the waterproof coat is added (which is typically gray or white) to seal in the roof with an elastomeric foam layer.

The flexibility and waterproof seal of polyurethane roofs is enticing for many commercial building owners. Cracking and splits are less likely because of the flexibility of the materials, which can expand and contract as the outside temperature changes throughout the year. Unlike metal flat roofs, you do not have to tear off existing roof materials to make repairs; a new layer of spray foam can be added on top. The downfall of having a polyurethane spray foam roof installed is that it can only be installed during specific weather conditions. SPF cannot be installed if the existing roof has any ice, frost, or surface moisture, so scheduling an installation ahead of time can be difficult. If the professionals installing your roof aren’t careful, SPF also poses a risk of overspray getting onto surrounding equipment, cars, and the parking lot.

Asphalt Roofing

Built-Up Roofing (or BUR)

Does your roof have the appearance of tar or gravel? Are the flashings around your HVAC curbs covered in tar? Then you likely have what we call built-up roofing, or BUR. Built-up roofing is perhaps the flat roofing method that has been used the longest, as it’s been around for more than 100 years. In an asphalt BUR installation, a flexible, continuous membrane is created by alternating fabric layers (plies) with tar and aggregate layers. This creates a single membrane, rather than the asphalt shingles you commonly see on sloped roofs on residential buildings.

Asphalt BUR roofs offer more waterproofing than many other roofing types, and because of the gravel layers, they also offer extra fire resistance. The aggregate used also offers protection from ultra-violet rays. However, as with other roofing styles, there are some downsides. Built-up asphalt roofs take longer to install than other materials, and the installation usually involves hazardous fumes. This roofing style can also be more prone to wind and water damage than other roofing materials.

Modified Bitumen (or Mod Bit)

Modified Bitumen roofing is considered the updated, more modern version of an asphalt BUR. Mod bit roofing is also commonly referred to as a “rubber roof,” as it frequently has a rubber-like appearance because of its elasticity. If your roof has seams about 3 feet apart and has a granular look similar to the texture of an asphalt shingle up close, you likely have a modified bitumen roof. These roofs are installed in a two-ply system much of the time and contain a cap sheet, or top layer which provides the granular texture similar to asphalt shingles.

Modified bitumen’s light color and heat reflection make it a popular choice for business owners who are interested in additional insulation from the heat. It also performs well in cold conditions and does not become brittle even when the temperature is consistently below freezing, making it a popular choice in the colder parts of the U.S. A downside to mod bit roofing is that when installed with heat, it can be a fire hazard. It also has a considerably shorter lifespan than many other roofing materials and is prone to tearing, especially if it walked on regularly.

Single-Ply Membranes

EPDM/Thermoset Roofs

This is your classic rubber roof. EPDM stands for Ethylene Propylene Diene Monomer, the material used for membrane roofs. If your roof appears to be covered in rubber and the HVAC curbs or roof flashings also have rubber on them, you likely have an EPDM roof. If the roof has been adhered, it is probably black in color. If it is ballasted, it is covered in large stones or other ballast that can be removed to expose the rubber roof surface.

EPDM roofing materials are typically affordable, which makes them a popular choice among many business owners. They also offer fire resistance and are a longer-lasting roofing option than many, if correctly installed. Downsides to EPDM roofing include a more expensive installation cost when fully adhered, as well as a bigger potential for punctures when it’s not reinforced. Black rubber roofs also tend to be less visually attractive than other roofing options.

TPO and PVC/Thermoplastic

TPO (thermoplastic polyolefin) and PVC (polyvinyl chloride) roofs are another single-ply membrane roofing option. If your roof is a light or white color and is pulled tight over the building, looking a bit like a white rubber roof, you likely have a TPO or PVC roof. These single-membrane roofs are installed by either adhering or mechanically attaching with screws.

PVC roofs are engineered for strength, giving them one of the longest lifespans of many flat roof types. They are resistant to wind, fire, and chemicals, and they are also waterproof. A downside of PVC roofs is that they require your old roof to be removed to install, but this provides a solid foundation to create its waterproof seal. PVC is a commonly chosen material for many industries because of its resistance to chemicals that it may be exposed to in an industrial setting. The team at Duerson specializes in PVC roof installation, and we believe it to be one of the most durable materials that provides the most ROI for your investment because of its long lifespan.If you’re interested in getting your roof checked out after you learn what type of roof you have, give us a call. Our flat roofing specialists can do regular roof inspections and maintenance and offer guidance on when it may be time to repair your roof or install a new one.