EPDM rubber roofing comes in sheets big enough that a porch, a garage, or a flat addition usually needs no seam at all: Carlisle’s Sure-Seal is made up to 50 feet wide and 200 feet long. On a warehouse the same sheet size means a fraction of the seams a narrow roll would need, and seams are where flat roofs fail. The membrane is synthetic rubber made to ASTM D4637, in 45, 60, and 90 mil, plus a 75 mil reinforced version from Elevate. A mil is a thousandth of an inch.
Rubber’s other advantage here shows up on install day. Elevate notes its EPDM is easier to detail in cold weather below 40 degrees, and the standard requires the sheet to pass a brittleness test at 49 below. That matters on a November job in Eau Claire, when a porch roof’s corners and the flashing around its posts all have to be folded in the cold.
Where EPDM fits on homes and commercial buildings
On houses, EPDM covers the roofs too flat for shingles, which need at least a 2/12 pitch: porch and portico roofs, the flat top of an addition, a breezeway between house and garage, and the shallow shed dormers on some story-and-a-half homes. A quarter inch of fall per foot is the working target from the model building code, and Wisconsin’s own dwelling code says only that every roof must drain, so a dead-flat porch deck gets fall built in before the rubber goes down.
On commercial buildings, EPDM goes down three ways. Fully adhered sheet is glued to the insulation or cover board. Mechanically fastened roofs use a reinforced sheet held with plates and screws. Ballasted roofs are loose-laid and held down with river stone, which goes down fast but adds weight the structure has to be checked for.
How EPDM seams are made now
The seams are where rubber roofs have changed most. Older EPDM roofs were spliced with liquid adhesive, and those glued seams are the classic failure on a 20-year-old rubber roof. Today the makers’ standard seam is primer and seam tape: Carlisle’s SecurTAPE or factory-applied tape, Elevate’s QuickSeam. Cold changes the procedure but does not stop it; Carlisle’s instructions add steps for splicing below 40 degrees, including warming the splice with a hot-air gun. Carlisle’s restoration guide also draws the line between the two generations: old adhesive seams get overlaid with a six-inch cover strip, while taped seams are left alone unless one is failing.
What shortens an EPDM roof’s life
- Glued seams from an earlier generation. A roof with liquid-adhesive seams is on a clock that a taped roof is not.
- Shrinkage. InterNACHI’s inspection guide calls membrane shrinkage a common problem even on recent installations: the sheet tents at its terminations, wrinkles around penetrations, and can pull flashing loose.
- Petroleum and grease. Carlisle and Elevate both say to keep petroleum products, greases, oils, and animal fats off the membrane. On a restaurant roof that means managing grease from the exhaust fan. On a porch it means asphalt roof cement, the black tar sold in buckets at the hardware store, is the wrong patch for a rubber roof, because it is a petroleum product.
- Punctures from foot traffic, dropped tools, and branches, most of them near rooftop equipment.
Rubber gets patched with rubber, never tar. The flat roof repair page covers how the patch is made and how the leak gets found first, which is the harder half.
EPDM roofing cost in Eau Claire
A rubber roof on the flat section of a house runs about $7 to $16 per square foot installed, and a 200 square foot porch or addition roof usually lands between $1,500 and $3,500. Commercial EPDM falls in the $8 to $18 per square foot band of our other membrane work. The low end is a new sheet over a sound, dry deck with simple edges. The high end is a tear-off down to rotted boards, new insulation, and a roof crowded with vents and curbs to flash.
If the choice is between rubber and a white welded sheet, the TPO roofing page covers where TPO wins, and the commercial and flat roofing page compares every flat roof system we install.