Torch-applied modified bitumen on a 3,000 sq ft flat section of a house.

System: 2-Ply Torch-Applied SBS Modified Bitumen (Base + Cap Sheet)

Materials (per 100 sq ft / square):

• Base Sheet: SBS modified base sheet (e.g., CertainTeed Glasbase, GAF GSA) or 28 lb fiberglass base sheet (ASTM D4601) nailed to deck.
• Cap Sheet: Granule-surfaced SBS cap sheet (ASTM D6163/D6164, Type 1 Grade S).
• Flashings: SBS flashing strips (smooth or granule), metal edge (drip edge/gravel stop), cant strip (wood/perlite).
• Adhesives: Roofing cement (ASTM D4586) for detailing; primer for metal/wood.

Sequence (IRC R905.11 / NRCA Guidelines):

1. Deck Prep: Clean, dry, smooth OSB/plywood (min 7/16"). Repair defects. Slope min 1/4":12" (IRC R905.11.1).
2. Perimeter & Penetrations: Install wood blocking at edges/curbs. Prime metal/wood. Install cant strips at all 90° transitions (walls, curbs).
3. Base Sheet Attachment (Mechanical): Roll out base sheet perpendicular to slope. Side laps 3", end laps 6". Stagger end laps 36". Fastening: Cap nails (1" cap, ring shank) or tin caps + 11ga ring shank nails. Pattern: 9" o.c. at laps (2 rows), 12" o.c. in field (2 rows), 4" o.c. at perimeter/corners (IRC R905.11.3, FM 1-28/1-90). Do not torch base to deck.
4. Cap Sheet Installation (Torch-Applied): Roll out cap sheet same direction as base. Side laps 3", end laps 6" (staggered from base). Torch Technique: Propane torch (vapor withdrawal). Heat underside of roll and base sheet simultaneously until bitumen liquefies/strings (approx. 400–500°F). Push roll forward with foot/knee; do not kick. Laps: Side laps min 3" (granule-to-granule requires granule embedment or 3" bleed-out). End laps 6". Stagger 36". Back-nailing: Optional but recommended at slope transitions/head laps: nail 1" back from leading edge, cover with next roll.
5. Flashings (Two-Ply Minimum): Base Flashing: Torch smooth SBS flashing strip (12" min up wall/curb, 4" min onto field). Extend over cap sheet. Counter Flashing: Torch granule cap flashing over base flashing (min 4" lap). Terminate under counter

For a 3,000 sq ft flat roof section using torch-applied modified bitumen (APP or SBS), follow this code-compliant system and sequence per IBC 1507.11 and ASTM D6164/D6222:

System Components:

• Substrate: Clean, dry, structurally sound deck (plywood/OSB ≥15/32" or concrete). Repair defects; ensure ≤1/4" in 10-ft slope for drainage.
• Vapor Retarder (if required): 6-mil polyethylene or self-adhered sheet (per climate zone; IRC R905.11.2).
• Insulation (optional): Polyiso or EPS, fastened or adhered per manufacturer; staggered joints.
• Base Sheet: Fiberglass or polyester-reinforced modified bitumen, mechanically fastened or adhered (per IBC 1507.11.2).
• Cap Sheet: Torch-applied APP (atactic polypropylene) or SBS (styrene-butadiene-styrene) modified bitumen, minimum 120-mil thickness.
• Flashings: Same material, reinforced at penetrations, walls, and edges (IBC 1507.11.3).
• Surfacing: Granule-surfaced cap sheet (UV protection); or aluminum coating if smooth.

Sequence:

1. Prep: Remove debris, repair deck, ensure dryness (<15% moisture content).
2. Vapor Retarder: Install if required (seal laps 6"+, tape/seal penetrations).
3. Insulation: Lay and secure (mechanical fasteners or adhesive); stagger joints, seal gaps.
4. Base Sheet: Unroll, overlap 3"+ side laps, 6"+ end laps. Mechanically fasten per manufacturer (typically 6" o.c. at laps, 12" o.c. field). Do not torch base sheet unless self-adhered.
5. Cap Sheet: Position, overlap base sheet 3"+ side, 6"+ end. Torch underside evenly to melt asphalt and bond to substrate. Roll with weighted roller for full adhesion. Seal laps with heat.
6. Flashings: Apply to walls, curbs, drains using same torch method; seal with compatible mastic or flashing cement.
7. Detailing: Seal all penetrations (vents, pipes) with boot flashings and mastic.
8. Inspection: Check for voids, bubbles, incomplete bonds; repair immediately.

Critical Notes:

• Torch Safety: Require fire watch, extinguishers, and trained crew (OSHA 1926.150). Never torch over insulation or near combustibles without barrier.
• Code Compliance: Must meet ASTM D6164 (APP) or D6222 (SBS); third-party tested (UL, FM).
• Licensing: In most jurisdictions, this requires a licensed roofing contractor due to fire risk and complexity.
• Warranty: Follow manufacturer’s specs exactly for coverage.

*If unsure about substrate, vapor retarder need, or local amendments, consult a licensed roofing engineer or contractor. Improper application risks