The working
- 1. Pitch multiplier√(1 + (0 ÷ 12)²)× 1.000
- 2. Roof anglearctan(0 ÷ 12)0.0°
- 3. Roof surface2,000 sq ft footprint × 1.000 (Flat (0/12) pitch multiplier)2,000 sq ft
- 4. Squares to order2,000 ÷ 100 = 20.0 squares, + 10% waste (gable roof)22.0 squares
- 5. Installed2,000 sq ft × $4–$10 per sq ft (tpo membrane (flat roof), HomeGuide, Nov 7, 2025)$8,000 – $20,000
- 6. Tear-off2,000 sq ft × $1–$3 per sq ft to remove one layer (HomeGuide)$2,000 – $6,000
- 7. PermitFlat fee, set locally (HomeGuide, Fixr)$100 – $500
- 8. Installed totalSum, rounded to $100 under $10,000 and $500 above$10,000 – $26,500
Prices are published national installed ranges (mostly HomeGuide, updated Nov 7, 2025), the same ones the roof cost calculator uses, for a straightforward re-roof with one old layer torn off. They are not adjusted for your state; the calculator can do that. Decking repairs, access, steep or cut-up roofs and the contractor all move the final price, so get at least two written quotes.
Squares and the materials list come from the same math as the roof calculator, which works them out for your own measurements.
Flat roof by footprint
| Footprint | Roof surface | Squares | TPO membrane | Standing-seam metal |
|---|---|---|---|---|
| 1,000 sq ft | 1,000 sq ft | 10.0 | $5,100 – $13,500 | $10,000 – $19,500 |
| 1,500 sq ft | 1,500 sq ft | 15.0 | $7,600 – $20,000 | $15,000 – $29,000 |
| 2,000 sq ft | 2,000 sq ft | 20.0 | $10,000 – $26,500 | $20,000 – $38,500 |
| 2,500 sq ft | 2,500 sq ft | 25.0 | $12,500 – $33,000 | $25,000 – $48,000 |
| 3,000 sq ft | 3,000 sq ft | 30.0 | $15,000 – $39,500 | $30,000 – $57,500 |
Compared with nearby pitches (2,000 sq ft footprint)
| Pitch | Angle | Area multiplier | Walking it | TPO membrane |
|---|---|---|---|---|
| Flat (0/12) | 0.0° | × 1.000 | Flat roof | $10,000 – $26,500 |
| 1/12 | 4.8° | × 1.003 | Low slope | $10,000 – $26,500 |
| 2/12 | 9.5° | × 1.014 | Low slope | $10,000 – $27,000 |
Did hail hit your area? Insurance often covers hail damage. Check hail history for your city, with storm reports back to 1955.
Questions people ask
Do flat roofs need a pitch multiplier?
No. A flat or very low-slope roof has almost the same area as its footprint, so 2,000 sq ft of footprint is about 20 squares before waste.
What material goes on a flat roof?
Single-ply membranes such as TPO or EPDM, or modified bitumen. Published installed ranges are $4–$10 per sq ft for TPO and $3.50–$10 for EPDM (HomeGuide). Asphalt shingles need at least 2/12 under the IRC.
More roof cost guides
- 3/12 pitch roof: multiplier, angle and cost
- 4/12 pitch roof: multiplier, angle and cost
- 5/12 pitch roof: multiplier, angle and cost
- 6/12 pitch roof: multiplier, angle and cost
- 7/12 pitch roof: multiplier, angle and cost
- 8/12 pitch roof: multiplier, angle and cost
- 9/12 pitch roof: multiplier, angle and cost
- 10/12 pitch roof: multiplier, angle and cost
- 12/12 pitch roof: multiplier, angle and cost
- Roof cost for a 1,000 sq ft house
- Roof cost for a 1,200 sq ft house
- Roof cost for a 1,500 sq ft house
- Roof cost for a 1,800 sq ft house