Roof surface ≠ home footprint — measure correctly or your bid is off
Roof surface area is the actual square footage of all roof planes, not the footprint of the house. A 2,000-sqft house with a 6:12-pitch roof and modest overhangs has about 2,400–2,600 sqft of actual roof surface. Steeper pitches and more dormers push the multiplier higher. Roofers price per "square" — 100 sqft of roof surface — not per square foot of home.
Get the surface area from a satellite measurement service (most roofers use EagleView or Hover) or a manual measurement, not from your tax assessor card. Bids based on home footprint are systematically low. The calculator above takes the actual roof surface, so put the right number in.
See also: Siding Replacement Cost — $8–$25 per sqft of exterior wall. Often paired with a roof replacement for full envelope refresh.
Underlayment and flashing are where cheap roofs go to die in year 8
Shingles handle bulk water. Underlayment and flashing handle the wind-driven water that gets past shingles, ice dams in cold-climate eaves, and the wall-roof intersection at every dormer and chimney. A 30-year shingle over 15-pound felt and reused step flashing is a 12-year roof, not a 30-year roof.
Insist on synthetic underlayment over the full deck (not just felt), self-adhering ice & water shield at eaves up at least 24 inches past the heated wall line, in every valley, and around every penetration. New step flashing at every wall — re-using old step flashing under new shingles is the #1 source of "the roof is leaking and we just replaced it" callbacks.
Asphalt vs metal vs tile: lifecycle math, not sticker price
Architectural asphalt at the $7/sqft national mid-point is the price-performance sweet spot — 30-year material life in moderate climates, 20–22 years in hot southern sun. Metal standing seam at $11–$15/sqft lasts 40–60 years and reflects heat, but the upfront premium is 60–100%. Concrete or clay tile at the $15+ tier lasts 50+ years and is the right call in fire-zone or coastal climates, but adds structural load that some 1970s framing won't carry without engineering.
On a 25-year horizon, metal often beats asphalt on lifetime cost. On a 10-year horizon (selling soon), asphalt almost always wins. Buy the roof for the time you'll own the house, not for the contractor's best margin product.
Compare: Attic Conversion Cost — $50–$225 per sqft. Replace the roof and add livable square footage at the same time.
Storm damage and insurance claims change the math
If your roof failed from a covered peril (hail, wind), your homeowner's insurance likely covers replacement minus your deductible. Don't accept a "free roof" pitch from a door-knocker — the contractors who do this either inflate the claim (which is insurance fraud you co-sign), or they install the cheapest possible scope to pocket the difference.
Pull three independent bids, file the claim yourself, and use the calculator output as a sanity check on what the insurance adjuster offers. If the adjuster's number is more than 15% below the standard band for your region, request a re-inspection and provide your own bids as comp.
How regional multipliers move the same roof
A standard 2,000-sqft asphalt roof at the East South Central multiplier (0.88×) lands near $12,300 base. The same scope on the Pacific (1.22×) is $17,000 base, $19,500 with contingency. Roofing labor is highly variable by region — and storm-damage cycles in places like the Southeast, Texas, and the Plains drive premiums during peak season (April–October). If your roof isn't actively leaking, scheduling a replacement in February buys 10–15% off peak labor pricing.