Louisiana Roofing, Sheet Metal and Siding

Key Concepts

Measuring irregular roof plans — two equivalent methods (Roofing Construction and Estimating, Ch. 1, pp. 7–8, Examples 1-1 and 1-2): - Positive method: divide the roof into rectangles and add their areas. - Negative method: extend the roof lines to form one large rectangle, then subtract the areas that lie outside the actual roof. - Both yield identical results; use whichever requires fewer calculations.

Net vs. gross roof area (Ch. 1): The net area is the deck area to be covered. The gross area adds starter course, hip and ridge units, extra felt at ridges/hips/valleys, and cutting allowances at rakes, hips and valleys. A roofing square is 100 square feet.

Separate takeoff per slope (Ch. 1, Example 1-13): When the slope changes from one section to another, do a separate takeoff for each area with a different slope (e.g., a porch at 3:12 is figured separately from a 6:12 main roof).

Slope-factor conditions (Ch. 1, Figure 1-19 / Appendix A): The universal net-area formula applies only when all roof planes have the same slope and all hips and valleys are framed at 45 degrees with respect to the eaves.

Unequal slopes at a valley (Ch. 1, p. 22, Example 1-15): Multiply the run of the low-sloping roof by the appropriate factor from Appendix B (valley length factors).

Key Concepts

Deck inspection and acceptance criteria. Before applying roofing materials, NRCA recommends the roofing contractor and appropriate parties (general contractor, deck contractor, architect/engineer or designer, owner's representative) make a visual inspection of the deck surface to verify it is clean, dry, smooth and ready for roof system application. A deck should be broom clean, reasonably smooth, free of voids or depressions, and adequately attached, and should remain rigid so as not to deflect excessively under live loads. A roofing contractor only can inspect the surface and cannot assume responsibility for slope, structural integrity or method of attachment. If defects are found, corrections should be made and a second inspection held before roofing work begins, attended by the same parties. (NRCA Roofing Manual: Steep-slope Roof Systems—2025, Chapter 2—Roof Decks)

Plywood thickness by rafter spacing (asphalt shingles). NRCA recommends four-ply, nominal ¾-of-an-inch-thick (actual 23⁄32-of-an-inch) plywood for 24-inch rafter spacings, to provide adequate support and fastener pull-out resistance. (Section 2.1—Wood Panels)

Panel edge clips. NRCA recommends panel edge clips (H-clips) be used when wood panel sheathing of ½-inch nominal thickness (actual 15⁄32-inch) or less is installed over supporting members spaced at 24 inches on center. Plywood sheathing panels should be installed with about ⅛-of-an-inch minimum gaps at panel edges for expansion. (Section 2.1—Wood Panels)

Key Concepts

Asphalt shingles (NRCA Steep-slope Roof Systems 2025, Sec. 4 / 4.2) - Standard three-tab shingles are commonly 12 in. × 36 in.; laminated shingles are also called "dimensional" or "architectural." - Minimum four roofing nails per full-length three-tab strip shingle, in a horizontal line about ⅝ in. above the tops of the cutouts. At 18:12 and greater, NRCA recommends six nails plus hand-tabbing (asphalt roof cement spots ~1 in. diameter). - Nails must extend a minimum of ⅛ in. through the underside of plywood/wood panel decks less than ¾ in. thick; on wood plank or board decks nails should penetrate at least ¾ in. - Typical exposure: 5 in. for standard 36-in. strip shingles; 5⅝ in. for metric 39⅝-in. shingles. Most common offset is the 6-in. method for 36-in. shingles. - Starter course: end joints offset a minimum of 5 in. from the first course's end joints; fasten along a line 1½ in. to 3 in. above the downslope perimeter edges. - Wind classes: ASTM D3161 — Class A 60 mph, Class D 90 mph, Class F 110 mph. ASTM D7158 — Class D 90 mph, Class G 120 mph, Class H 150 mph. - Roofing Construction & Estimating, Ch. 4: offset patterns are 6-in. (halves), 5-in. (random) and 4-in. (thirds); the 4-in. pattern is used on low slopes 2 through 3 in 12, with full shingle again at the…

Key Concepts

Asphalt shingle materials and standards - Mineral additives ("fillers") are added to coating asphalt to "stabilize the bitumen, reduce its natural flow characteristics and increase fire resistance, making it more suitable as a coating material." Increasing UV transparency is not a purpose — granule surfacing protects against UV degradation. (NRCA Steep-slope Roof Systems 2025, §4.1—Asphalt Shingle Materials) - ASTM D3161 wind-resistance classes: Class A passes a fan-induced wind test at 60 mph; Class D at 90 mph; Class F at 110 mph. (NRCA §4.1—Wind Resistance) - AC438, "Acceptance Criteria for Alternative Asphalt Roofing Shingles," is a performance-based alternative to ASTM D3462 as a basis for code compliance. (NRCA §4.1—Asphalt Shingle Standards)

Roof decks and sheathing - NRCA recommends plywood roof sheathing meet or exceed PS 1, "Construction and Industrial Plywood." This applies across asphalt shingle, slate, tile, metal shingle, and wood shake/shingle systems. (NRCA §2.1—Wood Panels) - NRCA does not recommend OSB panels as a substrate for slate roof systems — because of concerns about long-term OSB performance and the long-term life expectancy of slate roof systems. (NRCA §2.1—Wood Panels, Slate Ch. 2) - Wood boards: widths typically 4 to 12 inches; NRCA suggests nominal 6-inch-wide boards "to prevent excessive movement and splitting." Boards thinner than nominal 1 inch are not strong enough to support roof loads. (NRCA §2.2—Wood Planks and Wood Boards) - Separately, Roofing Handbook Ch. 2 gives…

Key Concepts

Fall protection triggers and systems (Subpart M) - Roofing work on low-slope roofs requires fall protection at 6 ft (OSHA 1926 Subpart M trigger height). - A low-slope roof is "a roof having a slope less than or equal to 4 in 12 (vertical to horizontal)" (§1926.500(b)). - Warning line systems on low-slope roofs: line placed a minimum of 6 ft from the edge. - A personal fall arrest system must limit free fall to a maximum of 6 ft. - Vertical lifelines require 5,000 lb minimum breaking strength (29 CFR 1926). In the verified problem using a 250-lb worker and a maximum arresting force of 1,800 lb, the required lifeline breaking strength is still 5,000 lb — the figure does not scale with worker weight. - Key definitions at §1926.500(b): free fall distance, deceleration distance (additional vertical distance traveled, excluding lifeline elongation and free fall, before stopping), lanyard, lifeline, anchorage, hole (gap or void 2 inches or more in least dimension), opening (30 inches or more high and 18 inches or more wide).

Key Concepts

Reroofing terminology (NRCA Roofing Manual: Membrane Roof Systems—2023, Chapter 9, §9.1; NRCA Steep-slope Roof Systems—2025, Chapter 6, §6.1) - Reroofing: re-covering or tearing off and replacing an existing roof covering. - Re-covering: installing an additional roof covering over a prepared existing roof covering without removing it. - Replacement: removing the existing roof covering, repairing damaged substrate, installing new covering ("tear-off and replacement"). - Roof assembly = structural deck/substrate plus the roof system; roof system = every component above the deck.

Existing deck evaluation (NRCA Membrane Roof Systems—2023) - Steel decks: NRCA is concerned with structural capacity and fastener-holding power of decks lighter than 22 gauge (0.028 inches thick) (p. 289). - Lightweight insulating concrete: NRCA suggests a minimum of four pullout tests per continuous pour area; if results are below the minimum required system-specific pullout resistance, the LWIC should be removed and replaced (p. 289). A minimum ½-inch-thick insulation layer may be adhered over a mechanically attached base sheet to cover minor deck irregularities and begin reroofing (p. 289). - Wood panel (plywood/OSB) decks: holes up to approximately 10 inches wide may be covered with 24-gauge (0.025-inch-thick) steel plate overlapping the wood deck a minimum of 4 inches, secured with fasteners 4 inches on center (p. 293).