EPDM Roofing 101 • Important Facts and Guidelines
By Roof Online Staff • Updated July 1, 2022
Table of Contents
- Pictures of EPDM Roofing
- Introduction to EPDM Roofing
- Characteristics of EPDM Roofing
- Lifespans of EPDM Rubber Roof Systems
- Things That Damage EPDM Rubber Roof Membranes
- Related Pages
- Useful Links for EPDM Roofing Information
Pictures of EPDM Roofing
- Damage to Fully-Adhered EPDM Caused by Fastener Back-Out
- Roofers Installing Fully-Adhered EPDM Roofing
Introduction to EPDM Roofing
What is EPDM Roofing?
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 low-slope roof systems where sheets of EPDM rubber are joined together to make a waterproof roof membrane.
When people talk about “rubber” roofs, they are pretty much always talking about EPDM. EPDM is currently the only material that qualifies as rubber that is used to construct full roof systems.
Although non-reinforced EPDM tends to be easily punctured (by careless foot traffic or dropped tools, for example) EPDM roofing is noted for being hail-resistant, and rubber roof membranes are among the easiest to repair. Even people with no roofing experience should find it fairly easy to make simple repairs on an EPDM roof.
History of EPDM Roofing
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 rubber 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 Roofing
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 material used for roof flashings tend to deteriorate faster under the intense UV radiation of Texas than they do in a place like Chicago, for example.
Types of EPDM Roof Systems
Single-ply roof systems are normally referred to by the way the system is attached to the building: there are ballasted systems, fully-adhered systems, and mechanically-attached systems.
Ballasted EPDM roofing systems use the weight of river-washed stone (no sharp edges) or concrete pavers to hold the roof system in place. The insulation and the roof membrane are loose-laid over the roof deck, and the ballast is installed on top of the EPDM membrane.
Ballasted systems do not use fasteners or adhesives to attach the roof system to the roof deck.
Ballasted systems do not normally include the hard insulation cover board that the other systems use to provide impact resistance. The ballast itself provides the impact resistance.
Because of this, ballasted EPDM roofing is far more susceptible to punctures due to foot traffic than the other systems, as the ballast stone deteriorates over time and develops sharp edges, which careless footsteps can push down into the soft insulation under the membrane.
Fully-adhered EPDM roofing systems use adhesive to attach the entire roof membrane to the underlying insulation or insulation cover board. The insulation and cover board are typically fastened to the metal roof deck below with specialized roofing screws.
If the roof deck is structural concrete, adhesive may be used to hold all of layers of the roof system in place, instead of fasteners.
This system is called “fully-adhered” instead of simply “adhered” because all EPDM roof systems typically use some adhesive (at the field seams and at perimeter and penetration flashings).
Mechanically-attached EPDM roofing systems use long plastic or metal batten strips to hold the membrane in place. These battens are placed across the roof, on top of the EPDM membrane, usually at the edges of the individual sheets of EPDM that make up the field membrane.
The battens come with holes for fasteners pre-drilled in them, and once they are set in place, fasteners are screwed through them, down through the roof system and into the roof deck.
The battens are covered when the seam between the two sheets is completed, the batten securing the edge of one sheet covered by the seam edge of the EPDM sheet next to it.
Size of the EPDM Membrane Sheets
Individual sheets of EPDM rubber 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 EPDM reinforced with polyester scrim.
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 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 unreinforced sheets, but membranes manufactured with a polyester reinforcing scrim are also used where recommended or required, particularly in mechanically-attached systems.
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 material are used to form the flashings at the perimeter of the roof and at HVAC curbs and other penetrations through the roof. Uncured material is sometimes used on the corners of curbs or other locations with sharp angles.
Characteristics of EPDM Roofing
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 Roofing 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 final product.
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. The black membrane 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, a black roof membrane can actually reduce annual energy costs versus white roofing membranes.
White: White EPDM is also available and can 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 the white version of the material tends to be somewhat less durable than the black.
White rubber roofs are uncommon; it’s 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 than the regular black.
For a good article on white EPDM, see here.
EPDM is Elastomeric
“Elastomeric” refers to the ability of a material to stretch and return to its original dimensions without being damaged.
When new, the unreinforced material 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%.
EPDM is Thermoset
“Thermoset” means that after the 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 any 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 roofing together. (Thermoplastic roof membranes such as PVC or TPO, on the other hand, are always able be welded or otherwise altered using (very) hot air.)
Cured and Uncured Material
The completely chemically cross-linked material 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 the material are manufactured by not allowing the EPDM polymer chains to become fully cross-linked.
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 will deteriorate faster than the rest of the roof. Deteriorated flashings are a common culprit when it comes to roof leaks in older roofs, particularly the corner patches at curbed HVAC units.
Fully-cured EPDM is one of the most durable low-slope 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 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 the adhesive in the seams or a part of the roof system other than the field membrane material, which tends to be the last to go.
Lifespans of EPDM Rubber Roof Systems
If a rubber roof has been installed correctly, with high-quality workmanship and high-quality materials, the key determining factor in the length of the expected useful service life of the roof will be the thickness of the membrane material. The second most relevant factor is the method of attachment.
The thicker the membrane, the longer the system will last.
Fully-adhered membranes generally last longer than mechanically-attached membranes, which generally last longer than ballasted membranes.
The longest lasting type of EPDM roofing will normally be a 90-mil fully-adhered roof, which will typically last around 35 years.
The type with the shortest lifespan will normally be a 45-mil ballasted roof, which will typically last around 15 years.
See our chart showing the life expectancies of all kinds of roofing systems for a more detailed breakdown of the lifespans of the different systems, as well as the lengths of typical warranties.
These are general guidelines and any kind of roof can fail much earlier than its design lifespan if it is poorly maintained, subjected to damaging chemicals or foot traffic, improper alterations, or extreme weather events beyond what the roof is designed to handle.
Things That Damage EPDM Rubber Roof 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. See this chart for a long list of chemicals and whether you can expect them to damage EPDM.
Rubber roof membranes, especially unreinforced membranes, 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 roof leaks with this type of roof.
Special care should be taken when walking on older ballasted systems, as the ballast stone tends to crack and split over time due to thermal cycling. There are usually a large number of jagged stones all over a ballasted roof that you want to avoid stepping on with too much force. Tread lightly!
Compatibility with Asphalt
EPDM roofing is not generally compatible with asphalt, although temporary contact with pure asphalt or polymer-modified asphalt is not something to worry about. However, EPDM is completely incompatible with solvent-based asphaltic roofing materials, such as roofing cement or roofing mastic.
These materials 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. The solvents in these products will quickly damage EPDM roofing membranes.
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 (we’re looking at you, HVAC mechanics) will spill petroleum-based fluids on a roof and fail to immediately and completely clean it up.
Within weeks a contaminated EPDM roofing membrane will wrinkle and start to break down; the material at the location of the spill will grow thinner and weaker, and eventually small holes will appear.
It’s a good idea to check the area where anyone has been working up on your roof as soon as they finish, in case you need to have them do a better job cleaning up
A major concern with EPDM roofing is restaurant exhaust. It’s very common to see severe roof damage around kitchen exhaust fans as kitchen grease accumulates on the surface of the roof. Kitchen grease affects EPDM roofing much the same way that petroleum products do.
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 roofing already damaged by grease will have to be removed and replaced. It should not be left in place and simply covered up by a patch, as the patch may also become contaminated.
Property managers should keep a close 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.
If a new tenant is opening a restaurant, whether or not the space has been used as a restaurant before, that is a particularly good time to inspect the roof. Have someone check to make sure they aren’t making unauthorized roof penetrations. Make certain that they’ve installed adequate protection for the roof around the new kitchen exhaust vents.
- EPDM Roofing Manufacturers
- EPDM Rubber Roof Repair: DIY Guide
- PVC Roofing
- TPO Roofing
- Types of Single Ply Roof Membranes
Useful Links for EPDM Roofing Information
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).
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.
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.