NRCA EPDM cheat sheet

EPDM membranes are thermoset (crosslinked) rubber; seams cannot be heat- or solvent-welded like thermoplastic, so field seams use adhesive splicing, splice tape, or uncured EPDM cover tape-not hot-air welding.

Standard unreinforced EPDM sheet thicknesses in North America are commonly 45 mil (0.045 in) and 60 mil; reinforced (polyester- or scrim-reinforced) sheets are commonly made in 60 mil and 75 mil.

Adhesive splicing requires cleaned membrane (splice cleaner), dry surfaces, and controlled temperature; most adhesive manufacturers set a minimum application temperature near 40–50°F (about 4–10°C) and prohibit splicing in rain or standing moisture.

Lap width for adhesive-spliced seams is typically 3 in minimum for factory-applied tape and 4–6 in for field-applied adhesive systems, per membrane manufacturer instructions; always defer to the specific system's published lap.

Seam continuity check: probe or visually inspect the full seam, especially at T-joints and inside/outside corners; T-joints should be staggered, not aligned, and covered with a splice or uncured cover strip where required.

Attachment methods: fully adhered (bonding adhesive or factory-applied adhesive), mechanically attached (fasteners and plates through membrane or batten bars), ballasted (river rock or pavers over protection layer), and induction-welded (coated plates).

Roof system components in order: structural deck, vapor retarder (as designed), insulation, cover board or substrate, membrane, and any ballast or coating; membrane must be separated from incompatible substrates (e.g., polystyrene) with a compatible separator.

Termination options: perimeter edge metal (drip edge, gravel stop, coping), reglet/counterflashing, and termination bars with sealant; membrane must extend above the waterline and be fastened/terminated per detail, not left loose.

EPDM is highly UV- and ozone-resistant but swells in contact with petroleum-based products (asphalt, some oils, grease, solvent-based sealants); use compatible separators and avoid direct contact with asphalt products.

Ponding water accelerates membrane aging and seam stress; design and construction should provide positive slope (commonly 1/4 in per foot minimum for drainage) and avoid low spots; EPDM can tolerate incidental ponding but not sustained standing water over seams.

Wind uplift performance depends on attachment density and edge restraint; perimeter and corner zones require closer fastener spacing and heavier edge securement than the field-follow the uplift design (e.g., FM or code-based) rather than uniform spacing.

Seam strength is the critical performance metric: adhesive-spliced seams should be tested by probe or peel where specified; a failed seam is typically caused by contamination, moisture, low temperature, or insufficient pressure/roller use.

Rolling seams with a hand roller (typically 1–2 in wide steel roller) immediately after mating improves adhesive contact and seam integrity; roller direction should be from the center of the lap outward to expel air.

Flashing details: pipe boots (pre-molded EPDM boots) with stainless or coated clamps; wall flashing with termination bar and counterflashing; drain and scupper flanges sealed and clamped, not just adhered.

Protection: EPDM must be protected from construction traffic, sharp edges, and incompatible chemicals; walkway pads or pavers are used at high-traffic and service areas.

Inspection hold points: substrate flatness and dryness before membrane, seam preparation, seam completion, flashing/termination, and final roof-each is a documented checkpoint in a quality-assurance program.

Cure time for splice adhesive and lap sealant matters: allow specified open/assembly time before loading or water exposure; premature water contact can debond seams.

Repair principles: clean and dry the area, cut back damaged membrane to sound material, install a patch with minimum 3 in overlap beyond the damage, and use the same splicing system as the original seam.