How to Calculate Metal Roofing Materials
Metal roofing is sold by the panel or linear foot. Accurate estimation requires calculating true roof area from footprint and pitch, then dividing by panel coverage. Also plan for ridge cap, valley flashing, rake trim, eave drip edge, closure strips, and the correct fasteners.
Panel Count Formula
Where Across equals building length divided by effective panel width, and Rows equals rafter length divided by panel length.
System Comparison
| System | Installed / sq ft | Life | Min Pitch |
|---|---|---|---|
| Exposed fastener (R-panel) | 8 to 14 USD | 25 to 40 yr | 3/12 |
| Corrugated | 7 to 12 USD | 20 to 30 yr | 3/12 |
| Standing seam | 12 to 25 USD | 40 to 70 yr | 2/12 |
Panel Coverage vs. Overall Width
Metal panels have two width measurements. The overall (physical) width is wider than the effective (coverage) width because panels overlap each other at the seams. Always use the effective width to calculate panel count:
| Panel Type | Overall Width | Coverage Width |
|---|---|---|
| R-panel (PBR) | 38 in | 36 in |
| 5V Crimp | 26 in | 24 in |
| Corrugated | 27-1/8 in | 26 in |
| Standing Seam (1") | 17 in | 16 in |
Accessory Checklist
A complete metal roof requires more than just field panels. Budget for every accessory listed or you will make multiple trips back to the supplier:
- Ridge cap - matches panel profile, one piece per ridge length
- Eave drip / starter trim - full eave length
- Rake trim - each gable edge x 2 sides
- Valley metal - W-valley or open valley flashing
- Sidewall and endwall flashing - where roof meets vertical walls
- Closure strips - foam or metal, ridge and eave seal
- Pipe boots - one per vent penetration, rated for metal
- Screws - manufacturer's rubber-washered self-tapping, 1 per sq ft minimum