Estimating, Damage Assessment and Construction Fundamentals
Measurement fundamentals
Estimating starts with geometry. Roof area equals footprint area multiplied by a pitch factor (4/12 = 1.054, 6/12 = 1.118, 8/12 = 1.202, 12/12 = 1.414). One roofing square equals 100 square feet. Add a waste factor - commonly 10% for simple roofs, more for hip and cut-up roofs - then round up. Interior work is measured as surface area; drywall comes in 4x8 and 4x12 sheets, and partial-height replacement is limited by existing texture lines and code requirements.
Line items and pricing
Modern estimates are line-item based: quantity times unit cost, plus material sales tax, permits, debris removal, and general conditions. Overhead and profit is typically applied when the scope requires three or more trades or a general contractor; the usual convention is 10% overhead plus 10% profit applied to labor and material subtotals. Code-upgrade items - the Florida Building Code rule that replacing more than 25% of a roof area triggers whole-roof code compliance, impact glazing, hurricane straps, and secondary water barriers - must be supported by the code citation.
Depreciation, betterment and matching
Depreciation reflects age and condition; betterment is an improvement beyond pre-loss condition and is generally not owed. Matching: replacing only the damaged slope may be unreasonable where the result cannot reasonably match the undamaged slope - document discontinued shingles, size or color differences, and visible contrast.
Worked example
A gable roof measures 32 ft × 40 ft = 1,280 sq ft at 6/12 pitch. Apply the factor: 1,280 × 1.118 = 1,431 sq ft = 14.31 squares. Add 10% waste = 15.7, round up to 16 squares. Order 16 squares, not 14.