If you have a flat roof, a flat roof coating will make your life a whole lot easier. While flat roofs are eco-friendly, affordable, and easy to repair, they’re also prone to impact and water damage. A flat roof coating protects against water, weather, and impact damage while sealing seams and cracks. To choose the right coating for your roof, explore the best types of flat roof coatings.
What is Flat Roof Coating?
A flat roof coating is an elastomeric coating that seals your roof, including cracks and seams, with a seamless membrane. It’s applied as a liquid and then hardens into an elastic membrane.
The elasticity is essential as it expands and contracts with structural movement. The thicker the application, the stretchier the roof membrane, but the recommended thickness is 30 dry mil, about the thickness of a credit card. A flat roof coating is an easy and affordable way to prolong the life of your flat roof.
Note: Mil is the unit of measurement for coatings, equalling one-thousandth of an inch or 25.4 microns. It does not stand for millimeters. Coatings shrink as they dry, so wet mil refers to the thickness of a wet coating, and dry mil refers to the thickness of a dry coating. Mil is used for anything applied in coats, including roof coatings and paint.
Best Types of Flat Roof Coatings
While there are many types of flat roof coatings, some stand out against the rest. Acrylic, asphalt emulsion, polyurethane, and silicone roof coatings work well with both commercial and residential flat roofs. Let’s dive in to learn more about the best types of roof coatings.
Acrylic
Originally, acrylic coating was created to give ultraviolet protection for sprayed urethane foam applications. Today, it’s used on a variety of roofs, including metal, modified bitumen, single-ply, EPDM, and built-up roofs (BUR). Acrylic roof coating is water-based, making it fire-resistant, and comes in white, tan, or gray. It’s often used in high UV environments due to its high reflectability.
When it comes to acrylic coating application, avoid extreme cold or heat and ponding water. High heat and ponding water affect adhesion, and cold weather will freeze it before you can apply it correctly.
Asphalt Emulsion
Asphalt emulsion is a combination of asphalt, bentonite clay, and water. The ingredients are broken down into smaller molecules using a specialty tool called the colloid mill. It’s used on BUR roofs, modified bitumen, coal tar pitch, TPO, EPDM, Hypalon and gravel roofs. It can also be applied to existing roofs or used to fix damaged roofs.
Because asphalt emulsion is water-based, apply the coating when the temperatures are above 50 degrees. However, once it’s cured, the coating holds up against extreme temperatures and temperature changes. Asphalt emulsion coating is water-proof, non-flammable, non-fibrous, and virtually odorless.
Polyurethane
Polyurethane coatings were created for sprayed-in-place polyurethane foam insulation, but it’s now used on a variety of roofs. It’s very durable and often used in areas prone to hail and high foot traffic on the roof surface.
Polyurethane coatings are solvent-based and have two different types: aliphatic and aromatic. Aliphatic urethane coatings are often used as a top coat because it’s UV stable, dirt-resistant, and holds color longer. Aromatic urethane coatings are less expensive but don’t stand up well against UV rays, so they’re often used as a base coat or substrate.
Silicone
Silicone is a solvent-based coating that is highly elastic and adheres well to existing roofs. It’s a solid choice, especially for homeowners, due to its exceptional water-proof qualities. While all coatings have a level of water resistance, silicone stands up the best against rain and ponding water. It also offers exceptional UV protection and withstands extreme temperature fluctuations.
Available in white, tan or gray, silicone coating works best on metal, modified bitumen, single-ply, EPDM, built-up roofs, and spray polyurethane foam. Silicone coating is chip and weather-resistant but susceptible to abrasions, meaning it shouldn’t be used in high foot traffic areas. It also tends to hold dirt, reducing reflectivity, so occasional cleaning is recommended.
Other Flat Roof Coatings
If you’re looking for something else, there are other flat roof coatings available. Here are some additional flat roof coating options.
- Butyl resins: Very durable and flexible, but its color fades quickly, and once cured, the membrane is thin.
- Fluoropolymer: Vibrant, lasting color and excellent adhesion, but expensive and susceptible to scuffs and scratches.
- PMMA: Very water-resistant and resistant to organic waste like bird droppings, but installation is expensive.
- Polyurea: Very strong, low wear-rate, chemical and corrosion resistant, but it yellows over time and is complicated to install.
- PUMA: Long lasting and chemical resistant, but doesn’t adhere well to all roof types (best with concrete, spray polyurethane foam, and metal).
- SEBS: Adheres to most roof types, is water resistant, and withstands foot traffic, but has low chemical resistance and a strong odor during application.
Benefits of Flat Roof Coatings
A flat roof coating has many benefits, including:
- Easy to apply: Applying roof coatings is quick and easy.
- Prevents roof leaks: The elastic membrane coats your roof, sealing any cracks and preventing leaks.
- Higher energy efficiency: A roof coating reflects sun rays, reducing the need for AC and improving your energy efficiency. It’s one of many ways your roof can save you energy.
- Reduces energy bills: With lower energy needs, your bill will go down.
- Lower maintenance needs: The roof coating reduces problems caused by water and debris. While you still need to clean and inspect your roof, you don’t have to do it as often. With the elastic membrane, you won’t need to fix leaks.
- Lowers maintenance costs: With reduced maintenance needs comes reduced maintenance cost.
- Extends the life of your roof: Because the roof coating is reflective, UV degradation is reduced, extending the life of your flat roof.
- Cost-effective: A roof coating is less expensive than a roof replacement (the average cost of flat roof replacement is $9,000)
- Variety: A variety of roof coatings are available, including acrylic, asphalt, polyurethane, and silicone. They also come in various colors, such as red, black, blue, brown, gray, green, tan, and white.
Disadvantages of Flat Roof Coatings
Nothing is perfect, including flat roof coatings. There are some disadvantages, including:
- Lifespan: Depending on the thickness, roof coatings are only warranted for 10-20 years, but a roof replacement can last 30 years.
- Not all roof types: Roofs with natural gaps cannot be sealed properly with a roof coating.
- Won’t fix everything: A roof with extensive damage will rot underneath the coating.
- Appearance: Depending on your preference, the overall appearance of your roof may not be improved.
FAQ About Flat Roof Coatings
Typically, flat roof coatings have a warranty of 10-20 years, depending on thickness. Typically, an elastomeric roof coating that’s 20 mils is warranted for 10 years, while a 30 mils coating is warranted for 20 years. It’s important to note that the lifespan may be longer than the warranty.
Conditions that affect a flat roof coating longevity include:
• Weather conditions
• Temperature
• Climates with temperature fluctuations
• Falling debris
• Foot traffic
• Water drainage
No, unfortunately, you cannot apply a flat roof coating to any flat roof. However, you can apply it to many.
You can apply a flat roof coating to these types of flat roofs:
• Modified Bitumen: Modified bitumen roofing is an asphalt-based rolled-roofing material that works well with a coating.
• EPDM: A rubber-based single-ply material. It’s often found on commercial roofs.
• Metal roof: Usually made from aluminum, copper, steel, tin, or zinc and works well with a flat roof coating. During application, ensure seams, screws, and penetrations are adequately coated. If rust is present, it will need a special primer.
• TPO: A thermos-plastic single-ply roof material that is very common on commercial buildings.
• Built-up roofing: Abbreviated BUR and also called tar and gravel, can be coated under certain circumstances. First, the gravel must be removed, and a primer must be applied.
• Spray foam roofing: Abbreviated SPF, spray foam roofing is usually applied over an existing roof. It works best with a silicone coating.
You cannot apply a flat roof coating to these types of flat roofs:
• Asphalt shingles: Asphalt shingle roof systems don’t work with roof coatings. The uneven shingled surface doesn’t allow for a seamless coating application.
• Tile roofs: Because tiles are often nailed down in overlapping rows, they have gaps in-between the rows and columns of tile. The gaps don’t allow the fluid-applied coating to form an effective membrane. Therefore flat roof coating doesn’t work on all types of tile roofing, including concrete, clay, and synthetic.
Solvent-based coatings, like polyurethane and silicone, usually last longer but are more expensive and require more care when applied.
Water-based coatings, like acrylic and asphalt emulsion, emit fewer odors and are more cost-effective but may not last as long.
Can I DIY My Flat Roof Coating, or Should I Hire a Professional?
Applying a flat roof coating is a simple DIY project. If you can paint, you can probably coat. However, DIY flat roof coating takes time, and time is precious. It’s also a little dangerous. Falls are the second most common cause of accidental home deaths.
If you’d rather enjoy your time with the people you love and the things you love doing instead of balancing precariously on your roof, consider choosing a roofing contractor. Roof Gnome can help. We’ll connect you with a highly-rated, local roofing professional. Your flat roof will be coated, sealed, and look fantastic in no time.
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