9.2 Steep-Slope Roofing, Sheet Metal & Flashing

9.2 Steep-Slope Roofing, Sheet Metal & Flashing

Steep-Slope Commercial Roofing Systems

For commercial structures featuring steep-slope architectural profiles (churches, educational facilities, hotels, office pavilions), two primary systems predominate:

1. Architectural Laminated Asphalt Shingles

• Slope Limitations: Standard installation requires a minimum slope of 4:12. Low-slope shingle application is permitted between 2:12 and 4:12 only if installed over a double layer of underlayment (ASTM D226 Type II #30 felt or synthetic underlayment overlapped 19 inches on each course).
• Fastening: Secured using corrosion-resistant 11-gauge or 12-gauge roofing nails with minimum 3/8" diameter heads. Fastener count and placement follow the shingle listing, manufacturer instructions, deck, and design wind condition; high-wind installations commonly require an enhanced pattern.
• Self-Adhering Ice and Water Barrier: Where the adopted code requires an ice barrier because of ice-dam history, install the specified compliant material from the eave to the required point inside the exterior wall line. Valleys and penetrations follow their separate approved details; Georgia does not make a cold-climate ice-barrier sentence universal to every roof.

2. Standing Seam Metal Roofing (SSMR)

• Panel Mechanics: Fabricated from 24-gauge or 22-gauge Galvalume-coated steel, aluminum, or copper. Vertical ribs (typically 1-1/2" to 2" high) contain male and female interlocking seams.
• Concealed Clip Fastening: Panels are anchored to structural purlins or solid wood decking using concealed clips folded into the seam. Concealed fastening eliminates exposed through-fasteners that back out and leak over time.
• Thermal Expansion Movement: SSMR panels expand and contract significantly under diurnal temperature swings. High-performance systems utilize two-piece sliding thermal clips that allow panels to glide longitudinally up to 2 inches without distorting or shearing fasteners.
• Minimum Slopes: Minimum slope depends on whether the panel is structural or architectural, seam geometry, sealant, substrate, listing, and manufacturer. Mechanically seamed structural panels may be approved at lower slopes than snap-lock panels; use the selected system rather than applying a generic 1/2:12 or 3:12 rule.

Roof Flashing & Sheet Metal Assemblies (SMACNA Standards)

Roofing leaks occur overwhelmingly at transitions, penetrations, and perimeter terminations rather than in the open field membrane. Flashing assemblies must strictly follow SMACNA and NRCA guidelines:

                PARAPET COPING & BASE FLASHING DETAIL
  ┌────────────────────────────────────────────────────────────┐
  │         CONTINUOUS CLEAT ──┐                               │
  │                            ▼                               │
  │                     ┌──────────────┐ ◄── SLOPED COPING CAP │
  │                     │ PARAPET WALL │     (MIN 1/4"/FT)     │
  │                     │              │                       │
  │                     │  REGLET CUT  │                       │
  │                     │   ┌──────┐   │                       │
  │                     └───┤ ┌────┴───┘ ◄── COUNTERFLASHING   │
  │                         │ │              (MIN 4" OVERLAP)  │
  │                         │ │                                │
  │                         │ └─────────┐ ◄── BASE FLASHING    │
  │                         │           │     (MIN 8" HEIGHT)  │
  │                         │   CANT    │                      │
  │                         │   STRIP   │                      │
  │                         │    /│     │                      │
  │                         │   /_│─────┴───────────────────── │
  │                         │ ROOF MEMBRANE & INSULATION       │
  └─────────────────────────┴──────────────────────────────────┘

Critical Flashing Components

• Base Flashing: The vertical continuation of the roof membrane extending up walls, curbs, and parapets. A common conventional detail carries base flashing at least 8 inches above the finished roof surface, but the roof-system manufacturer, project detail, curb, drainage geometry, and applicable standard control. Do not lower a specified height merely because a generic detail shows eight inches.
• Counterflashing (Cap Flashing): Sheet metal flashing attached to the vertical wall that turns down over the top edge of the base flashing with the overlap required by the approved system and project detail. Counterflashing protects the exposed top edge of the membrane from water intrusion.
• Reglets: Horizontal receiver grooves saw-cut into masonry mortar joints or cast into tilt-up concrete walls. The top hemmed flange of the counterflashing is inserted into the reglet, secured and sealed with compatible components at the spacing shown in the approved detail.
• Parapet Coping Caps: Formed sheet metal caps covering the top of parapet walls. Coping caps must feature:
  1. A sloped top surface (minimum 1/4" per foot) sloping inward back toward the roof membrane to prevent exterior facade staining.
  2. Continuous cleats (typically 20-gauge galvanized steel) fastened to both exterior and interior wall faces, allowing the coping cap to hook over the cleat hem without exposed face fasteners.
• Pipe Penetrations & Pitch Pockets: Cylindrical pipes are flashed using factory-molded EPDM/silicone pipe boots with stainless steel compression drawbands. For irregular structural penetrations (I-beams, steel angles), a formed sheet metal pitch pocket (penetration pan) is installed around the penetration, primed, and filled solid with non-shrink grout and topped with a 2-inch layer of pourable elastomeric polyurethane sealant.

Trace the drainage plane

At every eave, valley, sidewall, headwall, curb, pipe, ridge, and roof-to-wall intersection, trace where water lands and how each upslope layer laps over the next downslope layer. Flashing should shed water even before sealant is considered. Coordinate step flashing with wall underlayment and cladding, and place kick-out flashing where a roof edge discharges toward a wall. Preserve expansion joints and do not fasten fixed points through a sliding-metal detail. During closeout, inspect laps, hemmed edges, fastener zones, sealant compatibility, weeps, and termination bars against the approved shop drawings.