Alabama Roofing and Sheet Metal Contractor

Topic: Estimating and Plan Reading

Key Concepts

• Measure before you price. Measure the roof and calculate total area, then find the lengths of eaves, gables (rakes), ridges, hips and valleys. Use a 100-foot flexible tape with a grout hook; tapes highlighted at 5-inch intervals match the exposure of most composition shingles. Always make a sketch showing dimensions, slopes and penetrations. Errors in length and width matter far more than errors in ridge, hip or valley length (Ch. 1, Page 6).
• Positive vs. negative method. The positive method divides an irregular roof into rectangles and adds their areas; the negative method extends the roof lines to form one large rectangle, then subtracts the areas lying outside the actual roof. Both give identical results — use whichever requires fewer calculations (Ch. 1, Pages 7–8, Examples 1-1 and 1-2).
• Slope is rise in inches per 12 inches of run. A "6 in 12" roof rises 6 inches for every 12 inches of horizontal run (Page 10, Figure 1-9).
• Pitch is Total Rise ÷ Total Span, where span is the horizontal distance from one eave to the other; Slope = 2 × Pitch (Page 11, Equations 1-5 and 1-6).
• Roof slope can be read in degrees from the conversion table, Figure 1-12 (Page 12).
• Plan lengths of eaves and ridges are actual lengths because they run horizontally; sloping members must be converted with slope factors (Page 18).
• A roofing square is 100 square feet. Net roof area is the deck area to be covered; gross area adds starter courses, hip and ridge units, extra underlayment at ridges/hips/valleys, and cutting allowances at rakes, hips and valleys…

Alabama Roofing and Sheet Metal Contractor · 8 questions (13%)

Key Concepts

Roof deck slope - NRCA recommends roof deck slopes for asphalt shingle roof systems be specified at 4:12 or greater (NRCA Steep Slope, Section 2—Roof Decks). - Minimum slope for standard clay tile is 3 in 12; the underlayment spec calls for triple coverage with 30 lb felt followed by two plies of Type IV fiberglass at 3/12 and steeper (Underlayment on Sloping Roofs, Ch. 3).

Wood panel decks - Plywood for roof sheathing should meet or exceed PS 1, "Construction and Industrial Plywood" (NRCA Steep Slope, Section 2.1—Wood Panels). - NRCA minimums: four-ply, nominal ⅝-inch (actual 19/32") plywood at 16-inch rafter spacing; four-ply, nominal ¾-inch (actual 23/32") at 24-inch rafter spacing (Section 2.1). - Panel edge clips are recommended when panel sheathing of ½-inch nominal (actual 15/32") or less is installed over supports at 24 inches on center (Section 2.1). - Wood structural panel roof sheathing shall be manufactured with exterior glue (Exposure 1 or Exterior) (IBC 2304.8.2). Panels permanently exposed outdoors must be exterior type, except roof sheathing exposed on the underside, which may be Exposure 1 (IBC 2303.1.5). - APA recommends a minimum plywood grade of C-D Interior-and-Exterior Glue, or another equally durable exterior grade (Roof Sheathing, Decking and Loading, Ch. 2). - For OSB roof sheathing: "use a minimum ½ inch (nominal) panel" (Roofing Construction & Estimating, Ch. 2, p. 31).

Note: The SOURCE covers steep-slope systems, underlayments, and fire/wind classification. It does not address BUR composition, single-ply attachment methods, or roof insulation R-values, so those subtopics are not covered here.

Key Concepts

Material standards (IBC 2021) - Clay roof tile shall comply with ASTM C1167 (Section 1507.3.4); concrete roof tile shall comply with ASTM C1492 (Section 1507.3.5); slate shingles shall comply with ASTM C406 (Section 1507.7.5). - Asphalt shingles made from glass felt and surfaced with mineral granules: ASTM D3462, which addresses tear strength, fastener pull-through resistance, and pliability. NRCA recommends designers specify fiberglass-reinforced shingles complying with ASTM D3462 (NRCA Steep Slope, Section 4.1—Asphalt Shingle Standards). - Galvanized steel metal roof covering: minimum ASTM A653 G90 zinc-coated (IBC Table 1507.4.3(2)). Zinc roof covering minimum thickness 0.027 inch (IBC Table 1507.4.3(1)). - Wood shakes of naturally durable wood: minimum Grade 1 (IBC Table 1507.9.6). Wood shingles of naturally durable wood: Grade 1, 2, or 3, graded under CSSB rules (IBC Table 1507.8.5).

Minimum slopes (IBC 2021) - Slate: 4:12 or greater (Section 1507.7.2). Clay and concrete tile: 2½:12 (Section 1507.3.2). Metal roof shingles: not below 3:12 (Section 1507.5.2). NRCA recommends 4:12 minimum for slate and for metal shingle roof decks (NRCA Chapter 2—Roof Decks).

Fire classification (IBC 2021) - Class A = severe fire-test exposure (1505.2); Class B = moderate (1505.3); Class C = light (1505.4). Testing per ASTM E108 or UL 790 (1505.1). - Class A exceptions: minimum 16 oz/sq ft copper sheets over combustible decks (1505.2, Exc. 3); slate over ASTM D226 Type II underlayment over combustible decks (1505.2, Exc. 4). - Fire-retardant-treated wood shakes/shingles: impregnated by the full-cell vacuum-pressure process, per AWPA C1 (1505.6).

Key Concepts

Roof deck and sheathing - Boards 1x4 through 1x12 may be used for solid sheathing, but nothing wider than 1 x 6 is recommended — wider boards swell and shrink excessively after installation (Roofing Handbook, Ch. 2). - Plywood under a built-up roof must have a panel span index of not less than 32/16 (unsanded) or Group 1 (sanded) — 32 inches between rafters, 16 inches between floor joists (Roofing Handbook, Ch. 2, Plywood Sheathing). - With spaced sheathing, solid sheathing runs from the eaves up to 12 to 24 inches beyond the interior face of the exterior wall line; some codes specify 36 inches on slopes less than 4 in 12 (Roofing Handbook, Ch. 2, Spaced Board Sheathing).

Underlayment - Fiberglass felts cost about 65 percent more than organic felts of the same weight, but don't rot or absorb water and are fire resistant (Roofing Handbook, Ch. 3). - Eaves flashing (ice shield) on slopes 4 in 12 and steeper extends at least 12 inches beyond the interior face of the exterior wall line (some codes require 24 inches); on slopes less than 4 in 12 the requirement is 24 inches (Roofing Handbook, Ch. 3, Eaves Flashing). - NRCA's preferred eave detail with water and ice-dam protection membrane — used for tile (TILE(IL)-3), wood shake (WOOD SHK(S)-3) and slate (SLATE-3) — starts with a self-adhering stripping ply applied directly to the deck and turned down the fascia a minimum of 1 inch, then drip edge metal, then the membrane over the drip edge flange.

Key Concepts

Fall protection — roof slope drives the answer - Low-slope roofs (slope ≤ 4 in 12) with unprotected sides/edges 6 feet or more above lower levels: guardrail systems, safety net systems, personal fall arrest systems, or a combination of warning line system and safety monitoring system — §1926.501(b)(10). - Safety monitoring system alone (no warning line) is permitted only on low-slope roofs 50 feet (15.25 m) or less in width — §1926.501(b)(10); App. A to Subpart M explains width is the lesser of the two primary dimensions. - Steep roofs (slope greater than 4 in 12), 6 feet or more: guardrail systems with toeboards, safety net systems, or personal fall arrest systems only — §1926.501(b)(11). Warning lines and safety monitors are not options.

Warning line systems — §1926.502(f) - Erected around all sides of the roof work area. - No mechanical equipment: not less than 6 feet (1.8 m) from the roof edge — (f)(1)(i). - Mechanical equipment in use: 6 feet from the edge parallel to equipment operation, 10 feet (3.1 m) from the edge perpendicular to it — (f)(1)(ii). - Flagged at not more than 6-foot intervals; lowest point (including sag) no less than 34 inches, highest point no more than 39 inches; stanchions resist 16 pounds applied horizontally 30 inches above the surface; rope/wire/chain minimum tensile strength 500 pounds — (f)(2).