Sources & formulas

Every calculator on SidingCalcs rests on established wall/gable-area geometry plus stable siding conventions. Unlike topics with a time dependency, “verification” here is mathematical: each formula is tested against known values and is therefore correct for good. Here are the technical foundations by area.

Identities & geometry

  • Wall area: perimeter × wall height.
  • Gable area: ½ × base × height, per gable (sum all gables and dormers).
  • Net siding area: gross (walls + gables) − Σ openings (door ~21 sq ft, window ~15, patio door ~40, single garage ~63, double garage ~112 — labeled).
  • Siding squares: ceil(area × (1 + waste) ÷ 100), 1 square = 100 sq ft, rounded up.
  • Boxes / bundles: ceil(area × (1 + waste) ÷ coverage per unit).
  • House-wrap rolls: ceil(area × (1 + overlap) ÷ roll coverage), overlap ~10%.
  • Cost: (net area × your $/sq ft [or squares × your $/square] + labor + add-ons − discount) ×(1 + contingency).

Convention typicals (labeled)

  • Coverage / exposure per square by material: vinyl double-4″ ~200 sq ft/box (2 squares, 8″ exposure), cedar shingle ~25 sq ft/bundle (~5″ exposure), fiber cement / engineered / wood lap by the piece or square — labeled, confirm the manufacturer.
  • Waste factor by layout: ~10% simple, 10–12% average, 12–15% complex, 15%+ shakes/diagonal — labeled.
  • Standard deductions: door ~21 sq ft, window ~15, patio door ~40, single garage ~63, double garage ~112 — labeled.
  • Cost bands, story/access multipliers, lifespan, contingency ~10%: labeled planning typicals.
  • EPA RRP lead-safe rule: pre-1978 homes may have lead paint on old siding — follow the EPA Renovation, Repair and Painting rule and hire a certified firm for tear-off.

Cost tools

  • Every cost tool uses the prices you enter ($/sq ft, $/square, labor $, add-on $, $/lf) — no material or labor price is stored, so the site needs no maintenance. Cost bands are a labeled sanity guide.
  • Quote check: derived $/sq ft = quote ÷ area, compared to the labeled band for the material — a sanity flag, not a bid.

Material and labor prices, product data-sheet values and local rules vary by place and change over time — always measure your actual walls and gables and confirm coverage and exposure on the manufacturer’s installation instructions, allow extra for waste, trim and complex layouts, defer moisture/flashing, structural repairs, lead-paint abatement and code compliance to the EPA RRP rule and a certified professional, and get itemized written quotes from a licensed, insured siding contractor before you commit.