What are the differences between liquid-applied membranes and coatings?

AIA partner GAF explores how liquid-applied membranes and coatings differentiate by intended application.

Liquid-applied roof membranes (LAM) and roof coatings are not only here to stay, their use is on the rise. Both applications use common polymer-based materials, such as acrylics, silicones, and urethanes.  Polymer-based coatings are used on plaza decks, parking garages, balconies, playgrounds, and roofs, for example, to provide a level of weather resistance and an aesthetically pleasing surface. Polymer-based liquid-applied membranes are used as the weather-proofing layer for new roofs, replacement roofs, and roof re-cover systems. According to the Roof Coatings Manufacturers Association, “the most dramatic advance in coating properties has come in the past 40 years, with the development of polymers.” ¹  More information about these materials can be found here.

However, there can be confusion about liquid-applied membranes and coatings. The intended use of each product is different, yet many of the materials are the same for both applications. Depending on the design (intent) and application of polymer-based materials, they can be used to extend the life of an existing roof when used as a coating, or to provide a warranted, weathertight roof covering when used as a liquid-applied membrane.  

Market share

In 2017, The Freedonia Group published a research study titled, “Liquid-Applied Roof Coatings in the US by Product and Subregion.” According to that report, 11.85 million squares (1.185 billion square feet) of liquid-applied roof coating were installed in 2016.  Approximately 40% was installed in the South, with the remainder essentially evenly split between the Northeast, Midwest, and West regions.

The use of coatings and liquid-applied membranes is increasing for a number of additional reasons:  

• The use of materials that can be applied at ambient temperature is welcomed by an installer.  There are no super-heated materials or open flames, therefore reducing specific safety concerns.
• Materials are typically provided in containers sized for easy transport to and from rooftops.
• Common low-cost installation tools are used—brooms, brushes, squeegees; and simple, low-cost spray equipment.
• Using liquid-applied membranes can reduce waste created by a tear-off.
• These materials are commonly light colored, so they are reflective to help improve energy efficiency.

Defining the terms

The International Building Code (IBC) is a good place to start. The IBC says:  

“ROOF COATING. A fluid-applied, adhered coating used for roof maintenance or roof repair, or as a component of a roof covering system or roof assembly.”

IBC’s definition tells us three things: 1) coatings are fluid-applied and adhered, 2) coatings are used for maintenance or repair, and 3) coatings can be a component of a roof system or assembly.

Looking at how Chapter 15 of the IBC is arranged gives a bit of insight into IBC’s perspective on coatings and liquid-applied membranes. Section 1507, Requirements for Roof Coverings, has and continues to include all low-slope and steep-slope materials used as roof coverings that are recognized by the code.  Liquid-applied roofing has always been included in the list of roof coverings. Because liquid-applied membranes are considered to be roof coverings, roof systems with LAMs need to be tested for fire, wind, and impact … and acquire Approval Listings.

The IBC also states that the use of coatings on existing roofs is not considered reroofing. To that end, the 2021 IBC now includes Section 1509, Roof Coatings. The additional language added to the two recent versions of IBC has been an important step in distinguishing between coatings and liquid-applied membranes.  

Approval listings

Liquid-applied membranes are considered to be roof coverings by the IBC, and therefore they must be tested and have approval listings. Approval listings are used to show that systems have been tested and comply with the code requirements for roof system properties like fire-, wind-, and impact-resistance.  

To that end, searching for a roof system using the Assembly Search function within FM’s RoofNav software results in more than 10,000 Approval Listings for “Liquid Applied Systems” used for New Roofs used for new construction!  

Let’s chart it

The following chart provides examples of similarities and differences between coatings and liquid-applied membranes.

Conclusion

Simply put, coatings are used to provide protection from the elements and help extend service life.  Coatings are not installed as “membranes,” so they are not intended to seal leaks or be considered “waterproof” or “weatherproof.”  Liquid-applied membranes are considered to be just that—membranes—and are used as the roof covering in both new and re-cover roof systems. Liquid-applied membranes are tested as systems and have Approval Listings just like traditional asphaltic, modified bitumen, and single-ply roof systems.  

Learn more about coatings and liquid-applied membranes here.

References:

¹ RCMA.org/history-of-roof-coatings

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