A roof replacement quote is rarely one number. It is a stack of line items, and the same roof can come back at very different totals depending on what each roofer included. Understanding the layers lets you compare bids fairly instead of just picking the lowest one.
The roof replacement cost calculator is built around these layers: roof size in squares, an installed price per square by roof type, and optional tear-off. Here is what sits inside each one.
1. Roof size, in squares
Everything scales with roof area. Roofers measure in squares (100 square feet of roof surface), found from the footprint times the pitch multiplier. A 40 x 30 ft footprint at 6/12 is about 13.4 squares. See how to measure a roof for the steps.
2. Material and install labor
Most quotes bundle shingle material and installation into an installed price per square. Asphalt shingles commonly run about $350 to $850 per square installed, with 3-tab on the low end and architectural higher. Metal and slate are several times more.
| Roof type | Rough installed $/square | Notes |
|---|---|---|
| 3-tab asphalt | $350-$500 | Lowest cost, shorter life, flatter look |
| Architectural asphalt | $400-$850 | Most common today, better life and wind rating |
| Metal | $800-$1,400 | Long life, higher upfront cost |
| Slate | $1,500-$3,000 | Premium, heavy, specialized install |
3. Tear-off and disposal
Removing the old roof is labor plus dumpster and dump fees. One layer of asphalt commonly adds about $1 to $3 per square foot of roof area. Two layers, steep pitch, or tough access cost more. The cost calculator lets you toggle tear-off on or off.
4. Decking repair
The sheathing under the shingles is hidden until tear-off. Soft or rotted plywood has to be replaced, usually priced per sheet. A roof that has leaked for years can add several sheets. Ask how the roofer prices decking before signing.
5. Underlayment, flashing, and accessories
A complete roof is more than field shingles: underlayment, ice-and-water shield at eaves and valleys, drip edge, starter strip, ridge cap, step and counter flashing at walls and chimneys, pipe boots, and ridge vent. Reusing old flashing is cheaper but riskier; new flashing costs more and lasts.
6. Permits, overhead, and warranty
Permits, cleanup, magnetic nail sweep, crew overhead, and warranty tier all live in the price. A manufacturer system warranty may require specific underlayment and ventilation, which is part of why a "complete system" quote costs more than a bare shingle swap.
How to compare two quotes
- Confirm both used the same roof size in squares.
- Match the shingle line (brand, line, warranty).
- Check tear-off layers and disposal.
- Find the decking allowance and per-sheet price.
- List underlayment, ice-and-water, flashing, and ventilation.
- Read the warranty — installer, manufacturer, or both.
Put your roof into the roof replacement cost calculator, set the roof type and tear-off, and use the low-to-high range as a sanity check. If a quote sits far outside the range, the next move is to compare scope, not just price.
FAQ
How much does a new roof cost?
For a typical single-family asphalt shingle roof, a common planning range is roughly $8,000 to $15,000 installed, with smaller or larger, steeper, or premium roofs falling outside that. Roof size, type, pitch, tear-off, and region all move it.
How much of the cost is tear-off?
Removing one layer of old shingles plus disposal commonly adds about $1 to $3 per square foot of roof area. Extra layers, steep pitch, and difficult access push it up. New construction or an approved overlay skips it.
Why is decking sometimes an extra cost?
Roofers usually cannot see rotted or soft sheathing until the old roof is off. Many quotes include a per-sheet price for replacing bad decking, so the final invoice can rise if the deck is in poor shape.
Why do two roof quotes differ so much?
Different shingle grades, underlayment, ventilation, flashing replacement vs reuse, tear-off layers, decking allowances, warranty tiers, and overhead all change the number. Compare scope line by line, not just the total.