December, 2002
Inspection News and Views from the American Society of Home Inspectors

Understanding and Inspecting EPDM Roofing, Part 2


Continued from the November issue. EPDM (Ethylene Propylene Diene Monomer), or “rubber roofing,” is a type of single-ply roofing.

What to look for

EPDMFlashedWall.gifPreferably the inspection starts from the attic and/or under the roof. From this vantage point, you can look for stains and signs of leakage, and if possible, evaluate the sheathing condition prior to walking on the roof. Be watchful for and report rusty metal decking on a commercial building. (Photo: EPDM flashed wall.)

Most residential applications will have plywood decking with insulation below the decking. Plywood spacing must be maintained to allow for expansion. The plywood should be fastened down with screws (heads flush); use of “H” clips is not advisable. Ordinary nails will back out and puncture the membrane, and “H” clips will wear through. 

Commercial applications will almost always have insulation between decking and membrane. Insulation must have adequate fasteners to deck or curling/lifting of insulation will occur. On commercial roofs there is often a double layer of insulation, with the bottom mechanically fastened and the top stuck to bottom with hot asphalt or insulation adhesive. With this method, you will not be able to see the imprint of mechanical fasteners. Each EPDM brand has its own designed button fasteners, which is one way distributors identify their product after it’s installed, so you will see several different shapes of fasteners in the field.

Vents or no vents

There are two schools of thought regarding venting of the EPDM membrane:  some say ventilate, others say there’s no need to do so. Typically ventilation is always used on re-roof applications, but rarely seen on residential systems. The vents are intended to allow any moisture trapped in the old roof to escape when heated by the sun.

Without this, the membrane will blow up like a balloon. Generally, when the decking and insulation is dry, venting is not always needed. Many support the idea (including me) that “it’s better to have vents and not need them, than to need them and not have them.” The placement of vents can vary, but typically they are placed about every 20 feet. EPDM manufacturers do not recommend or require vents. They do require removing any wet roofing before re-covering, and state that doing so eliminates a need for vents. Manufacturers leave the decision to use a vapor barrier and/or vents to the building designer and/or the roofing contractor.

The lowdown on laps

If it seems soft under foot when you are walking on the roof, there could be moisture problems in the decking or insulation. Since laps can be a site of failure, check them as well as perimeter flashing closely, looking for separations, wrinkles, or openings. Manufacturer’s specifications on laps range from 3 inches to 8 inches, depending on the type of application and the specific membrane. Recently manufacturers are requiring laps to be sealed with a cured EPDM seam tape on 20-year warranty systems. Seam tapes make a premium splice and significantly increase installation costs. EPDM laps more typically will have a (black) splice cement with a required “Lap seal or edge caulk,” which looks like a rubbery black caulk. White splice cement and white caulk are available for use on white membranes. Lap sealants are designed to seal exposed edges on laps. The adhesive used to attach EPDM to decking is yellow, and cannot be used for laps.


Photo: Corner reinforcement overlay with edge caulk

Roof penetrations, wall flashing and anchor bars

Roof penetrations may have a “pitch pocket or pan,” which should be filled with an EPDM filler material (not roof cement). Wall flashing is usually an EPDM or a combination of EPDM and metal counter flashing – check for an adequate seal, and check for secure anchors or anchor bars. Anchor bars are made of extrude aluminum (1" wide) and come in 10-foot lengths. They are designed to hold membrane at walls and perimeters for the ballast system, and are also used in mechanical attached systems. Anchor bars should have fasteners every 6 inches on perimeters and every 12 inches when used as mechanical system anchors.


Photo: This is an access hole cut into EPDM flashed wall. Electricians needed to get to wiring in a wall behind a marquee sign. White caulk was not a proper fix.

Step by step, examine the roof

Check the entire roof for cuts, punctures and tears. Look for raindrop-size moisture spots. If you find one, look closely for a pinhole. Sometimes if there is enough moisture in substrate and there is a pinhole in the membrane, the heat of the sun will draw the moisture out of the pinhole creating a moisture spot.


Photo: EPDM patch

On a wet membrane, watch for air bubbles, which indicate a breech in the membrane. On commercial buildings, examine the areas around mechanical equipment and vents. On the roof of a restaurant, the greasy kitchen exhaust will often cause the membrane to soften, wrinkle and degrade. Check parapet walls and equipment curbs, looking for possible moisture entry points or lack of caulk. Look closely around mechanical fasteners for tearing. If the membrane is taut at the perimeter it probably has shrunk. Use caution when walking to avoid causing tearing at the mechanical fasteners.

Small bubbles or wrinkles in the membrane are typical. Bubbles form when the membrane is placed too quickly, that is before the adhesive is ready for placement. They are often more noticeable on newer roofs, and many times disappear as the roof ages. Wrinkles are easy to get as the membrane is placed, but difficult to get rid of, so often they’re ignored. Wrinkles and fish mouthing should have been cut out and patched, especially in laps. Wrinkles on laps and flashings for openings should be checked carefully. “T” joints in the membrane on a quality application will have a reinforcing 6-inch patch, and all edges will be caulked with lap seal. These joints require careful scrutiny. Corners should also be reinforced with patches, and all patches should have rounded corners and be caulked with lap seal/edge caulk.


Photo: This is an expansion joint between EPDM and modified
bitumen roofs.

Roof systems with insulation require a wood nailer around the eaves to provide a surface for attaching drip apron or gravel stop flashing. Drip apron/gravel stop flashing must have a minimum 3-inch flange and be stripped off with a 5-6 inch EPDM membrane.

Plumbing pipe collars require a one-piece (target type) EPDM membrane installed around them - 6 inches on all sides. Insulation on fully adhered systems must have 16 fasteners per 4 x 8-foot piece, on mechanical systems, six fasteners needed per piece. Fasteners are not required on ballast systems; the ballast holds the membrane down.

And that’s not all

Report bare spots in the ballast. Watch for shuffled, displaced, deflected or loose insulation. Check for bonding failure on fully adhered systems. Note any loose mechanical fasteners and anchors, especially on mechanical attached systems, and watch for tenting at underlying fasteners, which indicates it has backed up or that the insulation is overly compressed due to too much roof traffic. On commercial buildings with mechanical equipment, service trades will often accidentally damage the membrane, so you’ll want to check around roof-mounted equipment for damage or oil spills.

One manufacturer claims that 95 percent of EPDM failures are attributed to roof contractor error, 4.9 percent due to lack of care and maintenance of roof and only 1 percent attributed to manufacturing defects. Manufacturers recommend semi-annual inspections of an EPDM roof that include looking for all the obvious problems (failing seams or flashing, etc.), checking any roof drains, removing debris from roof, examining mechanical equipment for leaking oils, ponding, etc. It would probably be wise for a home inspector to recommend semi-annual inspections to the potential buyer.