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EPDM Roofing: Facts and Guidelines

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View of an older fully-adhered EPDM roof that has been patched in several places.

View of an older fully-adhered EPDM roof that has been patched in several places.

Applying adhesive to EPDM sheets during the installation of a fully-adhered EPDM roof.

Applying adhesive to field membrane sheets during the installation of a fully-adhered EPDM roof.

Pictures of EPDM Roofing

Introduction to EPDM Rubber Roofing

What is EPDM Rubber?

EPDM is a durable, waterproof, elastomeric, and highly flexible synthetic rubber which is well-suited for use as a single-ply roofing material for many reasons. “EPDM” is an acronym for “ethylene propylene diene monomer”, which is the full chemical name of EPDM rubber.

“EPDM roofing” refers to single-ply roof systems where sheets of EPDM rubber are joined together to make a waterproof roof membrane.

When people talk about “rubber” roofs, they are just about always talking about EPDM.

History of EPDM

EPDM was developed in the 1950’s and first used as a roofing membrane in the early 1960’s. By the 1980’s, it dominated the single-ply roofing market. It’s very common to find an older EPDM roof still in place on a building today; when properly installed and well-maintained, these roofs have been known to last for over 40 years.

Currently, EPDM is used in about 20% of all low-slope (“flat”) roof installations in North America each year, including both new construction and roof replacements.

Geography of EPDM Use

EPDM roofs are far more common in the north than in the south these days. Cheaper reflective white membranes such as TPO have largely replaced them in warmer climates due changing energy code and LEED requirements.

In addition, the uncured or semi-cured EPDM materials used for roof flashings tend to deteriorate faster under the intense UV radiation of Texas than they do in a climate like Chicago’s.

Types of EPDM Roof Systems

An EPDM roof system is referred to by the way it’s attached to the building: there are ballasted systems, fully-adhered systems, and mechanically-attached systems.

Although non-reinforced EPDM tends to be easily punctured (by careless foot traffic or dropped tools, for example) EPDM rubber is noted for being hail-resistant, and rubber roof membranes are among the easiest to repair.

Size of EPDM Membrane Sheets

Individual sheets of EPDM come in a variety of widths and lengths, with 10 ft. x 100 ft. being a typical size for large roof installations.

Much smaller pieces intended for use as membrane patches or for small flat areas on residential roofs are easy to find on Amazon.*

Standard membrane thicknesses are 45-mil (0.045 inches or 1.14 mm), 60-mil, and 90-mil for unreinforced EPDM, and 45-mil, 60-mil, and 75-mil for polyester-reinforced EPDM.

A leftover roll of 10 foot by 100 foot 60-mil EPDM lying on a new EPDM roof.

A leftover roll of 10 foot by 100 foot 60-mil field membrane lying on a newly-installed roof.

Chemical Composition of EPDM Rubber

EPDM is a synthetic rubber, ethylene propylene diene monomer (also called “ethylene propylene diene terpolymer” because it’s a polymer made from three monomers). The EPDM rubber used in roofing contains roughly 40% actual EPDM (EPDM base resin).

The other ingredients typically include carbon black (around 25%), plasticizing and extending oils (around 20%), with the remainder being various additives including anti-oxidants, anti-ozonants, fire retardants, curing agents, and inert fillers.

Most EPDM roofs in place today use sheets of unreinforced EPDM, but membranes manufactured with a polyester reinforcing scrim are also used where recommended or required, particularly in mechanically-attached systems.

Reinforced EPDM: You can see the reinforcing scrim in this defect photo of a fishmouth.

Reinforced EPDM: You can see the reinforcing scrim in this defect photo of a fishmouth.

Parts of an EPDM Roof System

Common components in this type of roof assembly are: the roof deck, an air or vapor barrier (if needed), one or more layers of insulation, a cover board (if needed), and the membrane itself, along with attachment components such as adhesives, fasteners, or ballast.

The field membrane (the vast majority of the surface of the roof) is formed from large sheets (typically 10 feet by 100 feet) of fully-cured EPDM rubber, seamed together with adhesives or adhesive tape during the roof installation.

Smaller pieces of fully-cured or semi-cured EPDM are used to form the flashings at the perimeter of the roof and at HVAC curbs and other penetrations through the roof. Uncured EPDM is sometimes used on the corners of curbs or other locations with sharp angles.

Characteristics of EPDM

EPDM is an elastomeric, thermoset, black or white synthetic rubber noted for its durability. It has good resistance to moisture, UV rays, heat, hail, ozone, and alkalis and acids. It has a high tensile strength, resists tearing, and remains flexible in cold weather (down to -45°F/-43°C).

EPDM Colors

Black: Sheets of EPDM are black because carbon black is added to them during the manufacturing process. As a raw material, carbon black is an extremely fine black powder, almost pure carbon, which is refined from petroleum or coal. It makes up about a quarter of the EPDM material typically used in roofing.

The addition of carbon black strengthens the EPDM resin, reinforcing its molecular structure and increasing its tensile strength. It also protects the polymeric chemical bonds of the material by blocking harmful UV rays, which is a critical function, and largely responsible for the excellent lifespan of rubber field membranes.

Because almost all EPDM roofs are black, they rarely qualify as “cool roofing” unless coated with a reflective roof coating. Black EPDM absorbs almost all of the heat from the sun’s rays during the day, and these roofs can reach temperatures of over 180 degrees on a hot afternoon. In warmer areas where cooling degree days outnumber heating degree days, black EPDM has generally been replaced as a single-ply roofing material by white PVC and TPO.

On the other hand, in colder climates where heating degree days outnumber cooling degree days, black EPDM can actually reduce annual energy costs versus white roofing membranes.

White: White EPDM is also available and allows EPDM to be used where a cool roof is called for.

White EPDM is formulated with a white pigment, typically titanium dioxide, in place of carbon black. Titanium dioxide is less UV resistant than carbon black, and as a result white EPDM tends to be somewhat less durable than black EPDM.

White rubber roofs are uncommon; white EPDM is more expensive than other white membrane materials and their share of the cool roof market is dwarfed by that of PVC and especially TPO. White EPDM is also more expensive.

For a good article on white EPDM, see here.

View of a white EPDM membrane. White single-ply roofing really shows the dirt!

An Elastomeric Material

“Elastomeric” refers to the ability of a material to stretch and return to its original dimensions without being damaged.

When new, the unreinforced EPDM normally used in ballasted or fully-adhered systems can typically stretch more than three times (300%) its original size without breaking, although this may be reduced somewhat as the membrane ages.

The reinforced EPDM normally used in mechanically-attached systems is constrained by the reinforcing polyester scrim, which reduces the elasticity of the roof membrane as a whole, and can only stretch about 35% before breaking.

For comparison, PVC roof membranes can only stretch about 15% before breaking, TPO membranes 27%, and an asphalt built-up roof about 2%.

A Thermoset Material

“Thermoset” means that after the EPDM polymer chains are cross-linked using heat and chemical curing agents during the manufacturing process, new molecular cross-links cannot be formed. The material is now heat-stable and future application of heat will either have no effect on it or will simply damage it (at very high temperatures).

In other words, after it’s manufactured, you can’t use a hot air welder on it. This is why adhesives or adhesive tape is required to join pieces of EPDM together. (Thermoplastic membranes such as PVC or TPO, on the other hand, can always be welded or otherwise altered using (very) hot air.)

Cured and Uncured Materials

The completely cross-linked EPDM used as a field membrane is also called “fully cured EPDM“.

Semi-cured and uncured EPDM are often used as a flashing material where the roof makes an angle change at walls, curbs, or roof penetrations such as vent stacks. These forms of EPDM are manufactured by not fully cross-linking the polymer chains.

This allows those materials to more easily conform to angles after installation without trying to snap back into a flat sheet shape like fully cured EPDM does.

It also means that these materials are more vulnerable to UV radiation and heat, and they deteriorate faster than the rest of the roof.

An uncured EPDM curb corner patch. See how easily it conforms to the angle changes - even at the air bubble (which should have been rolled out).

An uncured EPDM curb corner patch. See how easily it conforms to the angle changes – even at the air bubble (which should have been rolled out).

A Durable Material

Fully-cured EPDM is one of the most durable roofing materials available.

Due to its molecular stability, its exceptional resistance to UV radiation, and its non-reactivity in the presence of corrosive environmental substances such as water, acids, and ozone, the sheets of EPDM that make up a roof’s field membrane can remain functional for over 50 years.

When a rubber roof reaches the end of its service life, it’s almost always due to the failure of a part of the roof system other than the field membrane material, which tends to be the last to go.

Things that Damage EPDM Rubber Membranes

Rubber roof membranes are easily damaged by sharp objects, oils, gasoline and other fuels, grease, fats, and solvent-based asphalt compounds such as asphalt roof cement.

Sharp Objects

EPDM roof membranes, especially unreinforced EPDM, are fairly easy to puncture.

Dropped tools, nails or screws which are spilled on the roof and then stepped on, and even sharp stones caught in the tread of a boot have all been known to make holes. This is a common source of EPDM roof leaks.

EPDM Compatibility with Asphalt

EPDM is not generally compatible with asphalt, and is completely incompatible with asphalt-based roofing materials, such as roofing cement or mastic, which combine petroleum-derived solvents with asphalt to produce a workable, plastic asphalt that can be spread with a trowel or applied with a caulking gun.

Although EPDM can tolerate some forms of asphalt in some cases, to be safe you should never use an asphalt-based product on an EPDM roof.

Other Petroleum Products

Occasionally, other trades (looking at you, HVAC mechanics) will spill petroleum-based fluids on an EPDM roof and fail to immediately and completely clean it up.

Within weeks the contaminated EPDM will soften and wrinkle, and eventually the membrane at the location of the spill will grow thinner and weaker, and small holes through the membrane will usually appear.

It’s a good idea to check the area where anyone has been working up on your EPDM roof as soon as they finish.

Restaurant Grease

A major concern is restaurant exhaust. It’s very common to see severe roof damage around kitchen exhaust fans as grease accumulates on the surface of the roof.

Damage to the roof can be prevented by installing a protective layer of a more grease-resistant material (sheets of PVC roof membrane work well) around the exhaust location. This must be coupled with a good rooftop grease containment system.

Both of these things should be professionally installed, and they must be installed before the damage starts. EPDM already damaged by grease will have to be removed and replaced.

Property managers with EPDM roofs should keep an eye on their restaurant tenants. Restaurants seem to remodel their spaces more often than the average tenant, and they tend to make more unauthorized roof penetrations.

When a restaurant is moving into a space that has never been used as a restaurant before is a particularly good time to inspect the roof. Have someone check to make sure that they’ve adequately protected the roof around the new kitchen exhaust system.

1. General: See this in-depth general article about various roof systems on the Whole Building Design Guide site, which is maintained by the National Institute of Building Sciences.

2. General: For a decent general discussion of EPDM as a material, see the Wikipedia EPDM page. Not much information specific to EPDM roofing, though.

3. General: The EPDM Roofing Association has thorough and accurate information at this location (see the menu on the left side of the page for particular aspects of EPDM roofs). Just remember that this is an industry association that was formed with the purpose of providing “data documenting the many benefits of EPDM roofing systems” (quoted from their website).

4. General: Industry news can be found on the EPDM Roofing Association website.

5. Building Codes: “R905.12 Thermoset Single-Ply Roofing” from the 2015 International Residential Code and “1507.12 Thermoset Single-Ply Roofing” from the 2018 International Building Code. Both available on the UpCodes website.

6. Chemical Compatibility of EPDM: See this chart for a long list of chemicals and whether you can expect them to damage EPDM. Note that EPDM roof seam adhesive and semi-cured or uncured EPDM flashings may be affected differently than fully-cured EPDM field material. Chart is made available by Mykin Inc.

7. Hail Damage: “Comparative Performance of EPDM Rubber Roofing Membrane as Protection against Hail Damage” is worth a look. Good pictures; also pictures of hail damage to other roof types, not just EPDM. Available on the EPDM Roofing Association website.

8. Inspection of rubber roof systems: ROOFER: Membrane and Flashing Condition Indexes for Single-Ply Membrane Roofs – Inspection and Distress Manual is an extremely detailed and valuable resource put together by the US Army Corps of Engineers’ Engineer Research and Development Center. Available for download at the Defense Technical Information Center website.

9. Safety: See this material safety data sheet for health and safety information about EPDM at the Carlisle Syntec website. This is only an example and other products and brands may be different.

10. Technical: EPDM Roof Construction Details: An extensive list of easy-to-view details is provided on the GenFlex website.

11. Technical: See this product data sheet for the technical characteristics of EPDM roofing at the Johns Manville website. This is only an example and other products and brands may be different.

12. Technical: Ballasted EPDM, what is it? See this page on the Carlisle Syntec website.

13. Technical: See Carlisle’s Fully-Adhered EPDM page.

14. Technical: See Carlisle’s Mechanically-Attached EPDM.

15. Manufacturers: See this list EPDM roofing manufacturers.