NRCA EPDM key terms

A synthetic rubber membrane made from ethylene, propylene, and a diene monomer, supplied in large sheets. It resists ozone, UV, and weathering, making it a common choice for low-slope commercial roofing.

A membrane that cures or cross-links and cannot be re-melted or fusion-welded. EPDM is thermoset, so seams must be bonded with adhesive, tape, or a compatible splice method rather than heat welding.

A roofing membrane installed as one factory-made sheet or ply, rather than built up in layers on site. EPDM, TPO, and PVC are typical single-ply systems.

EPDM that has been vulcanized at the factory into a stable, elastic sheet. It is the standard membrane for fully adhered, mechanically attached, and ballasted roofs.

Non-vulcanized EPDM sheet that remains tacky and formable. It is used for flashing, inside and outside corners, and splice reinforcement, where it can conform to irregular shapes.

A contact adhesive applied to both membrane surfaces, allowed to dry, and pressed together to form a seam. Proper open time and roller pressure determine seam strength.

A pressure-sensitive tape, often butyl or EPDM-based, used to bond membrane laps. It offers a cleaner, faster alternative to solvent adhesive and requires careful alignment and roller pressure.

A liquid applied to the membrane before adhesive or tape to clean the surface and improve bond strength. Primer must dry fully before the splice is closed.

The lap joint where two membrane sheets overlap and are bonded together. Seam integrity is the most common source of EPDM roof leaks, so it receives focused inspection.

The overlapping edge of one membrane sheet over another. Lap width is specified by the manufacturer and must be maintained for a reliable bond.

A blunt tool run along a finished seam to check for voids, fishmouths, or unbonded edges. Probing is a standard quality-control step before the seam is accepted.

An opening or tunnel at the edge of a seam where the lap has not bonded. Fishmouths trap water and must be repaired before the roof is closed out.

An attachment method where the membrane is bonded over its entire underside to the substrate with adhesive. It resists wind uplift well and is common on high-wind or tall buildings.

An attachment method where the membrane is fastened to the deck with plates, bars, or screws, often at seams or in the field. Fastener spacing is set by wind-uplift design.

An assembly where the membrane is held down by gravel, pavers, or other weight instead of adhesive or fasteners. Ballast resists uplift but adds structural load and complicates leak detection.

Membrane or metal used to seal roof edges, penetrations, walls, and transitions. Flashing is a high-risk area for leaks and must be securely bonded and terminated.

The point where flashing or membrane ends and is secured and sealed against a wall, curb, or edge. A proper termination prevents water from getting behind the membrane.

Metal or other material installed over the top of flashing to shed water and protect the termination. It is often embedded in a reglet or fastened to the wall.

A groove cut or cast into a wall or curb that receives the top edge of counterflashing. It provides a water-shedding termination detail.

A corner where two walls or surfaces meet at an interior angle, requiring special flashing. Uncured EPDM or preformed corner pieces are used to avoid bridging and stress.

A corner where two surfaces meet at an exterior angle. It is flashed with a formed or field-fabricated piece that must be fully bonded and sealed.

A preformed EPDM flashing sleeve that seals around a pipe penetration. It is clamped or bonded to the pipe and bonded to the membrane at its base.

Any pipe, duct, vent, or structural element passing through the roof. Each penetration needs a dedicated flashing detail and a secure seal at the membrane.

A fitting that carries water from the roof surface into the drainage system. The membrane must be sealed to the drain flange and strainer to prevent leaks.

An opening through a parapet wall that allows roof water to drain. Scuppers require flashing and must be kept clear to avoid ponding.

A low wall at the roof edge. It affects wind uplift, requires flashing and coping, and must be included in termination and edge details.

The cap on top of a parapet wall that sheds water away from the wall. It protects the wall and the top of the flashing termination.

Metal installed at the roof perimeter to secure the membrane edge and shed water. It must be fastened and sealed to resist wind uplift and water entry.

The upward force of wind acting on a roof. EPDM systems are designed with attachment spacing, adhesives, or ballast to resist it.

Standing water on a roof that remains more than a short time after rain. It stresses seams and flashing and signals inadequate slope or drainage.

Rigid insulation cut to create slope toward drains or scuppers. It helps prevent ponding and is often part of the EPDM roof assembly.

A rigid board installed over insulation or deck to provide a smooth, firm surface for the membrane. It improves puncture resistance and can support fully adhered attachment.

The surface to which the membrane or insulation is attached, such as a deck, cover board, or existing roof. Substrate condition affects adhesion and fastener performance.

A layer that limits moisture vapor movement into the roof assembly. Its placement and continuity affect condensation risk and membrane performance.

Rigid board that provides thermal resistance in the roof assembly. It must be compatible with the membrane and attachment method and kept dry before installation.

A nondestructive inspection method, such as electronic leak detection or infrared, used to find breaches in the membrane. It complements visual inspection and seam probing.

A mastic-like compound used to seal edges and details where membrane and metal or other materials meet. It is not a substitute for a properly bonded splice.

A sealant applied at the exposed edge of a lap or flashing to block water entry. It is a secondary defense and should not replace a full bond.