ERA | EPDM Roofing Association

Design Questions

  1. What applications are suitable for EPDM membrane?
  2. What are the available thicknesses and types of EPDM single-ply membrane?
  3. Can EPDM membrane be used in roof top garden applications?
  4. How is EPDM membrane spliced together?
  5. What types of improvements have been made to EPDM splicing technology?
  6. Are EPDM membrane roofing assemblies fire retardant?
  7. Regarding aged EPDM membrane, what type of surface preparation is needed to perform any needed repairs?
  8. Would a manufacturer's warranty be terminated due to ponding?
  9. Can EPDM be installed at airport facilities where jet fuel exhaust is present?
  10. How does EPDM perform in expansion and contraction situations? Should relief or control joints be utilized the same as on a built-up roof?
  11. Can EPDM be coated or painted?
  12. Can EPDM be used in installations other than roofing?
  13. Can EPDM be used on freezer applications?
  14. What is the average unit weight of non-ballasted EPDM roofing systems?
  15. How long can an EPDM roofing system be warranted?
  16. How can drainage be enhanced on a flat roofing installation or roofs with 1/8 inch per foot or less slope?
  17. Can EPDM be used to retrofit an old metal panel roof?
  18. On an existing project, is it necessary to remove the old roof prior to the installation of a new EPDM roofing system?
  19. When retrofitting an older building, what steps can be taken to increase its energy efficiency when installing an EPDM roof system?
  20. Over what types of structural roof decks can an EPDM roofing system be installed?
  21. What are my options when designing an EPDM roof in areas where Seagull attack may be present?
  22. What is the water runoff coefficient of EPDM?

1. What applications are suitable for EPDM membrane?

EPDM membrane can be used for low and steep slope roofing, as well as unusually shaped structures (such as domes, barrels and other geometrically shaped roofs) due to its versatility. The membrane can be adhered, mechanically fastened, or loose laid. It can be installed above or below insulation (i.e., an IRMA application), and can also be used in below grade waterproofing applications.

Unlike most asphalt base products that are limited in their installation to a fully adhered application and have restrictions of ponded water, EPDM membrane can be used successfully in exposed or concealed assemblies due to its ability to withstand temperature extremes and resist the absorption of moisture.

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2. What are the available thicknesses and types of EPDM single-ply membrane? 

EPDM membrane is manufactured in various thicknesses (.045" to .090" thick) and is available as a non-reinforced or reinforced sheet (depending upon application). Other thicknesses are also available for use in non-roofing applications as a special order. 

Reinforced membranes contain an internal fabric that is completely encapsulated within the EPDM membrane sheet and is available in various thicknesses (.045" to .075"). Occasionally, a fleece layer can be added to the underside of the sheet that serves as a built-in underlayment for direct re-roof applications over certain types of existing roofing material. 

EPDM is also manufactured as vulcanized (cured) or non-vulcanized (uncured) membrane. Vulcanized membranes have set physical properties due to the vulcanization process and exhibit consistent behavior throughout the sheet that allow the membrane to have memory - this means when the membrane is stretched it will return to its original state. On the other hand, non-vulcanized EPDM does not have set physical properties because it is not cured when manufactured. This makes the uncured material ideal for use as flashing where the material can be stretched, formed, and shaped.

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3. Can EPDM membrane be used in roof top garden applications? 

EPDM has a proven track record in various waterproofing and pond lining applications which somewhat resemble roof top applications. However, there are certain rules that should be followed when designing a roof top garden regardless of the type of membrane used:

  • Select a membrane with high puncture resistance
  • Establish redundancy in the waterproofing assembly by overlaying splices
  • Design the assembly to provide slope and proper drainage at the membrane level
  • Incorporate protection above the membrane to aid against root growth and possible puncture
  • Incorporate a drainage layer and a root barrier to influence root growth away from membrane
  • Select proper growth media for the type of roof garden intended

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4. How is EPDM membrane spliced together? 

Two methods of splicing are currently available using either liquid adhesive or splice tape. 

When using liquid adhesive, adjoining sheets are cleaned with the manufacturer's recommended splice cleaner prior to applying the splicing adhesive. A sealant is used along the edge of the splice and is applied after allowing solvent in the adhesive to flash off (minimum 2 hours). Some manufactures have also used an additional sealant within the overlapping area that is applied immediately before putting the splice together. The sealant is intended as a secondary protection to guard against moist penetration in the event of workmanship error at intersections with factory seams. 

The second method of splicing was developed to speed up the seaming processing while maintaining consistent application across the entire seam. This process introduced the use of an adhesive tape in conjunction with a splice primer. The adjoining membranes are primed, and the tape is applied once the primer has dried. No additional sealant is used along the edge of the splice. This method has become more favorable due to application consistency.

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5. What types of improvements have been made to EPDM splicing technology? 

The introduction of membrane splice tapes as an option to the use of liquid adhesives has resulted in less reliability on contractor workmanship, increased production for the contractor, and enhanced performance for the roofing system and building owner. 

Laminated components (flashing components that have a pre-applied adhesive tape) have improved flashing quality (an item that has traditionally been problematic). 

Equipment utilized to install EPDM single-ply roofing systems has also evolved as well. Innovations have been made to ease the backbreaking work of roof installations - this helps reduce work force fatigue and enhances the installation and performance of the roofing system.

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6. Are EPDM membrane roofing assemblies fire retardant? 

An EPDM roofing assembly can be designed to meet Underwriters Laboratories (UL) and Factory Mutual (FM) fire classifications. As in many other roofing assemblies, the fire retardency level will depend on roof slope and the various components utilized. Current UL and FM publications contain numerous listings of various approved assemblies.

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7. Regarding aged EPDM membrane, what type of surface preparation is needed to perform any needed repairs? 

Because EPDM is a thermal set membrane at the time of installation, no additional curing will occur. Repairs can easily be performed with simple tools and accessories without the need of heavy-duty equipment. 

For example, a cut or tear can be repaired by cleaning the membrane surface to remove field dirt (brooming in addition to washing with low sudsing soap and rinsing). The area is then primed and a laminated patch is used to seal the cut or tear.

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8. Would a manufacturer's warranty be terminated due to ponding? 

Ponded water on an EPDM roofing system will not void a manufacturer's warranty or be the sole reason to deny issuance of a warranty. During the design phase, however, efforts should be made to incorporate positive drainage into the roofing assembly to avoid excessive ponding. It is beneficial to avoid ponding water due to the expense associated with its removal in the event of repairs and also to reduce moisture infiltration and damage in the event of incidental puncture.

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9. Can EPDM be installed at airport facilities where jet fuel exhaust is present? 

There is a misconception in the field that EPDM will degrade with exposure to jet fuel. This is unfounded because jet fuel is in a vapor form and the only degradation from petroleum products is caused by submerging EPDM in liquid petroleum over a prolonged period. There are numerous airport installations throughout North America, the Mideast, and the Far East where EPDM membrane was utilized.

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10. How does EPDM perform in expansion and contraction situations? Should relief or control joints be utilized the same as on a built-up roof? 

Relief or control joints are commonly used with built-up roofs to subdivide a larger roof area and segregate possible damage into one small area. EPDM, due to its flexibility (-49 F) and elongation, will accommodate stresses caused by temperature extremes, structural movement, and deflection. In cases where the building is designed with expansion joints, the design should be carried all the way through to the roof and an expansion joint should be incorporated into the roof design.

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11. Can EPDM be coated or painted? 

Acrylic coatings are available that can be applied directly to a prepared EPDM surface. Preparation usually consists of cleaning the EPDM with a pressure washer and a detergent solution or wash. Latex-based paint products can also be used, however, the EPDM manufacturer should be contacted prior to application to ensure compatibility and continuation of warranty coverage.

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12. Can EPDM be used in installations other than roofing? 

Yes. EPDM has been used in various installations such as pond liners, tunnels, foundations, thru-wall flashings, terraces, garden roofs, and RV roofs.

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13. Can EPDM be used on freezer applications? 

Freezer applications typically utilize thicker insulation with greater R value (R 40 and above) that subject the membrane to extreme conditions (very hot on a hot day and very cold on a cold day). EPDM is known for its ability to remain stable during temperature extremes and heat-aging testing indicates no changes to physical properties.

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14. What is the average unit weight of non-ballasted EPDM roofing systems? 

The weight of a roofing system varies depending on components used. After combining the weight of components (i.e. insulation, membrane, fasteners, and adhesive), typical installation weight is less than 2 pounds per square foot (10 kg per square meter) when .060" thick membrane (typically weighing 1/3 pound per square foot or 1.6 kg per square meter) is utilized.

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15. How long can an EPDM roofing system be warranted? 

Generally speaking, system warranties that cover material and labor costs are available. Different manufacturers offer various assemblies with standard warranties that vary from 5 and 10 to 15 and 20 years. In addition, premium coverage up to 30 years is available and can include coverage for higher wind speeds, incidental puncture, and hail resistance.

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16. How can drainage be enhanced on a flat roofing installation or roofs with 1/8 inch per foot or less slope? 

In addition to the number and size of roof drains, drains should be positioned in low areas to eliminate ponded areas. Also, crickets and saddles may be incorporated to divert water and reduce the accumulation of water. If necessary, tapered insulation may be incorporated throughout the roof or in localized areas where additional drainage is needed.

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17. Can EPDM be used to retrofit an old metal panel roof? 

Yes. Insulation is used as filler between the flutes (or ridges) of the metal roof panels and then overlaid with a rigid board. Both layers may be mechanically attached or adhered to the metal panel roof. The EPDM membrane is then adhered to the rigid insulation or mechanically fastened to the structural purlins beneath the metal roof.

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18. On an existing project, is it necessary to remove the old roof prior to the installation of a new EPDM roofing system? 

Even though most exiting roofing materials are totally removed in most applications, an old and existing roof may be left in place once the manufacturer's substrate preparations are followed. The existing roof and roof deck should, however, be inspected prior to re-roofing to ensure compatibility and structural integrity.

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19. When retrofitting an older building, what steps can be taken to increase its energy efficiency when installing an EPDM roof system? 

On an older building, lower counterflashings and terminations may hinder the use of thicker insulation; therefore, insulation with greater R Value per inch, like polyiso, may be used. Incorporating two (2) layers of insulation with staggered joints will certainly increase the insulation's thermal efficiency over using a single layer since heat loss through gaps will be minimized. When the use of multiple layers is not feasible, an inverted assembly may be used in which extruded polystyrene insulation is placed above the membrane.

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20. Over what types of structural roof decks can an EPDM roofing system be installed? 

The availability of a wide range of accessories and components make an EPDM roof system versatile. For example, the membrane can be adhered directly to wood and structural concrete decks, or mechanically anchored to steel decks. For decks with low pullout resistance (i.e., gypsum, fibrous cement and light gauge steel), special fastening components are available. Ballasted assemblies can be used on any deck as long as the structure is capable of supporting the weight of the installed system. The choice between an adhered, mechanically fastened, or a ballasted assembly may be influenced by the type of structure and its condition.

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21. What are my option when designing an EPDM roof in areas where Seagull attack may be present? 

The use of reinforced membranes over a rigid substrate such as Den-Deck, high density wood fiber board and plywood provide excellent protect and both pecking and the dropping of clams to break them open. Additionally placing pavers over any of the EPDM membrane thicknesses would also provide protect as would an IRMA roof system design. Special detailing of the corners, such as double flashings are also recommended. Designers and contractors are suggested to contact the manufacture for specific detailing concerns and potential puncture resistant warranties.

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22. What is the water runoff coefficient of EPDM? 

There is no exact figure as conditions such as rain water evaporation off a hot EPDM surface are difficult to test. The formula for calculating this flow is called the Maming Formula. The American Society of Plumbing Engineers Data Book suggests that initially there will be some friction along the drainage path but it will quickly go to zero. On a low slope fully adhered EPDM Roof with slope of 1/4" per foot one could justify a coefficient of .95 to .99. If calculating drainage flow for design or legal matters it is recommended that you contact a plumbing engineer, registered in the state in which the building in question is located.

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