Reference tables

Every figure here is used by at least one calculator on the site, and every page names its sources. When a source is updated, the table and the calculators that use it change together, and the date at the top of each page changes with them.

• Roof pitch factor table

  Pitch from 1/12 to 24/12 in degrees and percent, with the pitch factor, hip and valley factor and rafter length per foot of run, and what each pitch means for roofing.

• Shingle and roofing coverage table

  Bundles per square, starter and cap coverage, underlayment and ice barrier rolls net of laps, nails per square and waste allowances by roof shape.

• Roofing material weights per square

  Installed weight of every common roofing material per square and per square foot, and tear-off debris per layer, for dumpsters and dead load.

• Gutter and downspout sizing table

  Gutter capacity by rainfall intensity for 5 and 6 inch K-style and half-round gutters, the pitch allowance, and the roof area each downspout serves.

• Attic ventilation NFA table

  Net free vent area for attics from 600 to 3,000 sq ft under the 1:150 and 1:300 rules, with typical ratings of ridge, soffit and box vents.

• Standard sizes for roofing estimates

  The square and every stock size a roofing order is counted in: bundles, rolls, panels, trim, tile, slate, lumber, ladders, gutters and dumpsters.