NRCA Modified Bitumen cheat sheet

Modified bitumen = asphalt flux blended with a polymer modifier; SBS (styrene-butadiene-styrene) gives rubbery elastomeric behavior, APP (atactic polypropylene) gives plastomeric, more rigid behavior.

SBS membranes are typically installed with hot asphalt or cold adhesive because the polymer softens under direct flame; APP membranes are commonly torch-applied because the plastomer tolerates higher heat.

Carrier/reinforcement governs strength: polyester mat gives high tear and elongation (good for low-slope movement), fiberglass mat gives high tensile and dimensional stability but low elongation.

Granule surfacing protects the compound from UV; sand, talc, or film surfacing is used on ply sheets and on surfaces intended to receive adhesive or another ply.

Typical ASTM product standards: ASTM D6162 (SBS polyester/fiberglass), D6163 (SBS fiberglass), D6164 (SBS polyester), D6222 (APP polyester), D6223 (APP fiberglass); D6164-style products are 3.0 mm to 4.5 mm nominal thickness.

Membrane thickness classes are nominal (e.g., 180 mil ≈ 4.5 mm); torch grades carry a heat-resistant bottom film or sand that melts to bond, while self-adhered grades carry a removable release film over adhesive.

Storage rule: store rolls upright on pallets, out of standing water and direct sun; SBS compounds soften and block/deform in heat, and wet or dirty rolls contaminate laps and adhesive surfaces.

Manufacturing sequence: asphalt oxidation/blending → polymer dispersion at high shear and temperature → filler addition → coating onto carrier → surfacing application → cooling, trimming, and roll winding.

Deck deflection limit for most low-slope membrane roofs is L/360 of the span under design load; structural deck panels and their attachment are verified before any membrane work begins.

Steel deck: minimum 22 gage, fastened to supports; each panel end bearing per code, and side laps stitched or fastened per the deck manufacturer's span table.

Wood deck: minimum nominal 1 inch (19/32 in. plywood or 1 in. board) for membrane attachment; plywood/OSB joints must be supported and gaps kept about 1/8 in. for expansion.

Structural concrete decks must be cured, dry, and free of form-release agents, laitance, and dust; surface profile is achieved by shot blasting or grinding before priming.

Insulation is installed with staggered joints, no gaps over 1/4 in., and a cover board or approved substrate sheet where the membrane manufacturer requires it for torch or hot-applied work.

Vapor retarder placement: on the warm side of the insulation, continuous and sealed at laps and penetrations; a perforated or breathable retarder is used where drying to the interior is intended.

Substrate moisture: new lightweight insulating concrete and gypsum decks must be dry to the manufacturer's limit (often tested by calcium chloride or in-situ probes) before membrane or vapor retarder placement.

Roof slope for positive drainage: minimum 1/4 in. per foot (2%) for new construction; ponding water is defined as standing more than 48 hours after rain.

Base sheet attachment is either mechanical (fastener and plate rows), hot asphalt, cold adhesive, or torch; attachment method must match the manufacturer's approved system and the deck type.

Fastener density and row spacing follow the manufacturer's uplift/wind-load table for the building's design pressure; perimeter and corner zones require tighter spacing than the field.

Lap widths: side laps typically 3 in. and end laps 6 in. for base/ply sheets, but always per the membrane manufacturer's printed instructions.

Ply sheets are installed shingle-fashion (each ply lapping the previous) so water drains over the laps; stagger end laps between plies so they do not align.

Hot asphalt application temperature for built-up/modified systems is typically 400–440 °F at the kettle, with mopping temperature checked at the point of application; asphalt must not be heated above the flash point.

Cold adhesive: two-sided application (substrate and sheet) with a notched trowel, allowing the adhesive to become tacky before rolling; coverage rate per manufacturer, no voids.

Mechanically attached base sheets must be installed with the fastener head flush and the plate covered by the following ply; overdriven fasteners are defects and must be replaced.

Ply sheet orientation: run sheets perpendicular to the deck span or per manufacturer; offset end laps at least 12 in. between adjacent plies to avoid four-ply corner buildups.

Torch method: heat the bottom surfacing and the substrate until the compound flows (asphalt bleed visible at the lap), then roll the sheet into the molten bitumen; do not overheat (glossy, smoking, or charred compound indicates burnout).

Torch flame: use a wide fan tip, keep the flame moving, and heat the lap and the sheet simultaneously; a visible uniform asphalt bead at the lap edge confirms a watertight bond.

Hot asphalt method: membrane is embedded in a mopped or applied layer of ASTM D312 Type III or IV asphalt at proper temperature; the sheet is broomed to remove air and achieve full contact.

Cold adhesive method: applied with a notched trowel or spray; open time must be observed, and laps are sealed with adhesive or a lap sealant per the manufacturer.

Self-adhered method: primer is applied to the substrate and allowed to dry to touch; release film is removed progressively and the sheet is rolled with a weighted roller to achieve contact.

Lap sealing for torch and hot systems relies on the bitumen itself; for cold and self-adhered systems, laps may require a separate lap adhesive or sealant.

Surfacing orientation: granule-surfaced cap sheets face up; sanded or film-surfaced sides face down to receive the bonding bitumen; verify roll orientation by the printed side or release film.

Application temperature limits: cold adhesives and self-adhered products have minimum ambient and substrate temperatures (often 40–50 °F and rising); torch and hot work require dry substrate and no precipitation.

Base flashing height at walls is typically 8 in. minimum above the roof surface, with the top edge terminated in a reglet, counterflashing, or termination bar.

Flashing plies are applied shingle-fashion: the base ply goes on first, then the cap or finish ply, each extending onto the field membrane at least 4 in. and up the wall per detail.

Termination bar: fastened at the top of the flashing at maximum 12 in. on center with a sealant bead over the fastener heads; counterflashing must overlap the membrane flashing at least 4 in.

Penetration details: a target or pitch pan is used for clusters and irregular penetrations; a penetration seal (boot) is used for single pipes, with the flange set in membrane adhesive or hot asphalt.

Inside and outside corners are reinforced with a pre-formed corner or a folded membrane piece; never stretch a single ply around a 90° corner.

Drain and scupper flanges are set in a bed of membrane adhesive or hot asphalt, clamped with the strainer, and the flange is stripped with a minimum 6 in. wide reinforcing ply.

Expansion joints: use a pre-manufactured expansion joint cover or a two-ply flashing assembly with a loop that accommodates movement; do not bridge the joint with a rigidly bonded single ply.

Reglet and counterflashing must be water-tight at the top; a sealant bead is installed in the reglet and the counterflashing is set into it, with the membrane flashing terminating below the counterflashing.

Torch work requires a hot-work permit, a fire watch, and a fire extinguisher (minimum 2A:10BC or per local code) at the work area before ignition.

Remove or protect combustible materials within 35 ft of torch work; cover or shield combustible decking, insulation, and adjacent roof surfaces.

Never torch directly over combustible insulation, wood decks, or existing combustible roofing without an approved thermal barrier or protection board.

Two-person rule for torch work: a fire watch must remain on site during work and for a minimum of 1 hour after the last torch is shut off (verify local code; some jurisdictions require longer).

LP-gas cylinders must be stored upright, secured, and away from heat; keep cylinders at least 10 ft from torches and open flames and follow the 1:1 or local ratio for cylinder storage.

Personal protective equipment: flame-resistant clothing, leather gloves, eye protection, and a face shield; torch hoses and regulators are inspected for leaks before each use.

Kettle safety: keep asphalt below the flash point, never add cold or wet asphalt to hot asphalt, and maintain a lid and a fire extinguisher at the kettle.

Hot asphalt burns: immediately cool a burn with water and seek medical attention; do not apply ice or grease, and report all burns per the site safety plan.

Common defects: fishmouths (open laps), wrinkles, blisters, ridging, bare spots, and inadequate lap widths; fishmouths are cut back to sound membrane and patched with a minimum 6 in. overlap.

Blister repair: cut the blister open, dry the area, and install a patch extending at least 6 in. beyond the cut; large or widespread blistering may require membrane replacement.

Lap inspection: probe laps for voids; a properly bonded torch lap shows a continuous asphalt bead at the edge with no voids or unbonded areas when probed.

Ponding water: standing water more than 48 hours after rain indicates inadequate slope or deflection; corrective action is re-sloping or drainage modification, not just patching.

Code references: IBC Chapter 15 (roofing) and Chapter 16 (wind/uplift), and ASCE 7 for wind and snow loads; FM Global and UL ratings govern uplift and fire classification.

Fire classification: Class A, B, or C assemblies per ASTM E108/UL 790; Class A is required in many jurisdictions for roofs over combustible decks.

Warranty inspection: manufacturer's inspections typically occur at completion and after 5 years; punch-list items must be corrected before the warranty is issued.

Repair materials must be compatible with the existing membrane; SBS and APP compounds are generally not compatible in direct bonding, and repairs should use the same product family and surfacing.

SBS = styrene-butadiene-styrene, an elastomer; APP = atactic polypropylene, a plastomer.

Polyester mat: high tear and elongation. Fiberglass mat: high tensile, low elongation.

ASTM D6164 covers SBS polyester; D6222 covers APP polyester.

Nominal thickness classes run about 3.0 mm to 4.5 mm (180 mil).

Granules face up for UV; sand or film faces down for bonding.

Store rolls upright, out of water and direct sun; heat deforms SBS.

Torch grades carry a heat-sensitive bottom film or sand that melts to bond.

Manufacturing: blend/oxidize asphalt, disperse polymer, add filler, coat carrier, surface, cool, wind.

Deck deflection limit: L/360 of span under design load for low-slope membrane roofs.

Steel deck minimum 22 gage, fastened to supports, side laps stitched per span table.

Wood deck minimum nominal 1 in. (19/32 in. plywood); joints supported, ~1/8 in. gaps.

Concrete decks: cured, dry, free of laitance and form-release agents; shot blast or grind.

Insulation joints staggered, gaps ≤ 1/4 in.; cover board where manufacturer requires.

Vapor retarder goes on the warm side, continuous, sealed at laps and penetrations.

New lightweight concrete and gypsum decks must be dry to manufacturer's moisture limit.

Minimum slope 1/4 in. per foot (2%); ponding = water standing > 48 hours.

Base sheet attachment: mechanical, hot asphalt, cold adhesive, or torch, matching the approved system.

Fastener rows and density per manufacturer's uplift table; tighter spacing at perimeter and corners.

Typical laps: 3 in. side, 6 in. end, per manufacturer's printed instructions.

Ply sheets shingle-fashion so water drains over laps; stagger end laps between plies.

Hot asphalt at the kettle typically 400–440 °F; never exceed flash point.

Cold adhesive: two-sided application with notched trowel; observe open time; no voids.

Overdriven or flush-proud fasteners are defects and must be replaced.

Offset end laps at least 12 in. between adjacent plies to avoid four-ply buildups.

Torch: heat until asphalt bleeds at the lap, then roll in; glossy or charred compound = burnout.

Torch flame: wide fan tip, keep moving, heat lap and sheet together; look for a continuous asphalt bead.

Hot asphalt: embed membrane in ASTM D312 Type III/IV at proper temperature; broom out air.

Cold adhesive: notched trowel or spray; observe open time; seal laps with adhesive or lap sealant.

Self-adhered: prime substrate, dry to touch, remove release film progressively, roll with weighted roller.

Torch and hot systems bond by bitumen; cold and self-adhered laps may need lap adhesive or sealant.

Granule cap sheet faces up; sanded/film side faces down to receive bonding bitumen.

Cold and self-adhered products have minimum ambient/substrate temperatures (often 40–50 °F and rising).

Base flashing height typically 8 in. minimum above the roof surface.

Top edge terminated in a reglet, counterflashing, or termination bar; sealant bead over fasteners.

Flashing plies shingle-fashion: base ply first, then cap ply, each extending ≥ 4 in. onto field.

Termination bar fasteners at maximum 12 in. on center; counterflashing overlaps ≥ 4 in.

Pitch pan for clusters and irregular penetrations; boot for single pipes, flange set in adhesive.

Inside and outside corners reinforced with pre-formed corner or folded membrane piece.

Drain flanges set in adhesive or hot asphalt, clamped with strainer, stripped with ≥ 6 in. ply.

Expansion joints use a pre-manufactured cover or a two-ply loop assembly; never rigidly bridge.

Hot-work permit, fire watch, and extinguisher (minimum 2A:10BC) at the area before ignition.

Remove or protect combustibles within 35 ft of torch work; shield combustible decking and insulation.

Never torch over combustible insulation, wood decks, or existing combustible roofing without a thermal barrier.

Fire watch remains during work and at least 1 hour after the last torch is shut off (verify local code).

LP-gas cylinders upright, secured, away from heat; at least 10 ft from torches and flames.

PPE: flame-resistant clothing, leather gloves, eye protection, face shield; inspect hoses and regulators.

Kettle: keep below flash point, never add cold or wet asphalt to hot, keep lid and extinguisher.

Hot asphalt burn: cool with water and seek medical attention; do not apply ice or grease.

Fishmouths: cut back to sound membrane, patch with minimum 6 in. overlap.

Blister repair: cut open, dry, patch ≥ 6 in. beyond the cut; widespread blistering may need replacement.

Probe laps for voids; a good torch lap shows a continuous asphalt bead with no unbonded areas.

Ponding > 48 hours after rain indicates inadequate slope or deflection; correct by re-sloping or drainage.

Code: IBC Chapter 15 (roofing), Chapter 16 (wind/uplift), ASCE 7 for wind and snow loads.

Fire classification: Class A, B, or C per ASTM E108/UL 790; Class A often required over combustible decks.

Manufacturer warranty inspections typically at completion and after 5 years; punch-list items corrected first.

Repairs must use the same product family and surfacing; SBS and APP compounds generally do not bond directly.