Estimating, Plan Reading, and Project Planning
Reading the drawings
Start with the roof plan, then check slope notations, ridge and valley lines, sections, details, and general notes. Sections reveal insulation thickness and flashing heights that the plan hides; details show the flashing sequence. Note scale, north arrow, and any reference to manufacturer requirements. Build a quantity list by linear and area items: field area, starter, ridge and hip, valley, rake and eave edge metal, penetrations, and flashing.
Squares and waste
Roofing is measured in squares of 100 sq ft. Plan area must be converted to sloped area with a pitch multiplier: about 1.03 at 3:12, 1.12 at 6:12, 1.20 at 8:12, 1.30 at 10:12, 1.41 at 12:12. Add waste: about 10 percent for simple gable roofs and 15 percent or more for hips, valleys, and complex geometry. A three-tab shingle typically covers about 33.3 sq ft per bundle, so three bundles per square; confirm the actual bundle coverage printed on the wrapper for architectural products. Ridge cap and starter are separate line items, as are underlayment rolls (about 400 sq ft nominal) and fasteners.
Planning
Sequence deliveries so bundles are not stacked at the ridge; plan staging, dumpster location, ladder access, and a fall-protection plan. Include permit fees, tear-off and disposal, decking replacement allowance, and labor productivity factors in the bid.
Traps
Using footprint area without the pitch multiplier, forgetting starter and ridge cap, and ignoring tear-off and disposal costs.
Worked example
A 40 ft by 30 ft hip roof at 6:12: 1,200 sq ft footprint times 1.12 equals about 1,344 sq ft, or 13.4 squares; add 10 percent waste for about 15 squares, then price starter, hip and ridge cap separately.