Estimating, Plans, and Specifications
From drawings to numbers
Estimating starts with reading the plans: roof plan, elevations, sections, and the general notes that specify materials, slopes, and code references. Know how to compute roof area from the footprint using the slope factor (roof area = footprint area × slope factor). Know that waste factors vary by complexity - simple gable roofs ~10%, complex hip-and-valley roofs 15–20% or more.
Know the takeoff checklist: field shingles, starter, ridge cap, hip/ridge, underlayment, ice barrier, drip edge, valley material, flashing, fasteners, ventilation, and labor. Specifications (Division 07 in CSI MasterFormat) control submittals, warranties, and approved manufacturers - questions often test that the spec governs over a verbal instruction or a generic habit.
Traps: confusing plan dimensions with roof dimensions; forgetting to include ventilation and flashing in the bid; ignoring change order procedures when the scope changes; and misreading scale on a drawing.
Worked example: a 30 × 40 ft footprint (1,200 sq ft) with a 6:12 slope has roof area = 1,200 × 1.118 ≈ 1,342 sq ft, or about 13.4 squares. Add 10% waste = ~14.8 squares; round up to 15 squares for ordering.
Rule of thumb: measure twice, apply the slope factor, add waste, and confirm against the spec - never bid from memory.