Roof Pitch: What It Means & the Minimum for Each Roofing
By Marko VisicBSc Physics, University of Ljubljana
Pitch decides which roofing a roof can take and what has to go under it.
the lowest pitch for asphalt shingles
What roof pitch means
Pitch counts the inches a roof rises over each foot of level run. A 6/12 roof climbs 6 inches for every 12 inches you move in from the eave, the same tilt as 26.6° or a 50% slope. You will also see it as 6:12 or “6 on 12”; they all mean the same roof.
The roof pitch chart converts every pitch to degrees and percent, and the roof pitch calculator finds your own roof’s pitch from a measured rise and run, an angle or the building’s width.
Roof pitch vs roof slope
Building codes say slope. The 2021 IRC writes it as units vertical in 12 units horizontal, with the percent beside it: asphalt shingles go on slopes of 2 units vertical in 12 units horizontal or more. That is what most people call pitch.
Carpenters once meant something else. In the traditional sense, pitch is the rise divided by the span, the full width of the building, not the run. Swanson Tool’s rafter handbook still gives the conversion, 24 × pitch = rise per foot, so an old plan’s “quarter pitch” is a 6/12 roof.
Minimum roof pitch for shingles
The 2021 IRC lets asphalt shingles go on any roof of 2 in 12 or steeper. From 2 in 12 up to 4 in 12 it requires double underlayment. The rule is the same for 3-tab and architectural shingles, since both are asphalt shingles.
Makers say the same on their data sheets: CertainTeed’s Landmark is for roofs with slopes greater than 2 inches per foot. Other shingles start higher: wood shingles and shakes at 3 in 12, metal shingles at 3 in 12 and slate at 4 in 12. Solar shingles share asphalt’s 2 in 12.
Minimum pitch by roofing material
Section R905 of the 2021 IRC sets a least slope for every roof covering. The table gives each in pitch and degrees. Below 2/12 the list is down to roll roofing and low-slope systems such as membranes, built-up roofs and spray foam.
| Roofing | Minimum pitch | Angle | IRC section | Note |
|---|---|---|---|---|
| Asphalt shingles | 2/12 | 9.5° | R905.2.2 | Double underlayment from 2/12 up to 4/12 |
| Clay and concrete tile | 2½/12 | 11.8° | R905.3.2 | Double underlayment from 2½/12 to 4/12 |
| Metal roof shingles | 3/12 | 14.0° | R905.4.2 | |
| Mineral-surfaced roll roofing | 1/12 | 4.8° | R905.5.2 | |
| Slate shingles | 4/12 | 18.4° | R905.6.2 | |
| Wood shingles | 3/12 | 14.0° | R905.7.2 | |
| Wood shakes | 3/12 | 14.0° | R905.8.2 | |
| Metal roof panels, lapped seams | 3/12 | 14.0° | R905.10.2 | ½/12 with lap sealant; ¼/12 standing seam |
| Built-up roofs | ¼/12 | 1.2° | R905.9.1 | ⅛/12 for coal-tar built-up roofs |
| Modified bitumen | ¼/12 | 1.2° | R905.11.1 | |
| Thermoset single-ply | ¼/12 | 1.2° | R905.12.1 | |
| Thermoplastic single-ply | ¼/12 | 1.2° | R905.13.1 | |
| Sprayed polyurethane foam | ¼/12 | 1.2° | R905.14.1 | |
| Liquid-applied roofing | ¼/12 | 1.2° | R905.15.1 | |
| Photovoltaic shingles | 2/12 | 9.5° | R905.16.2 | |
| BIPV roof panels | 2/12 | 9.5° | R905.17.2 |
Low-slope and steep roofs
OSHA draws the line at 4/12. A roof of 4 in 12 or less is a low-slope roof, and anything greater than 4 in 12 is a steep roof. On a steep roof, anyone working 6 feet or more above a lower level needs guardrails with toeboards, a safety net or a personal fall arrest system.
The roofing rules and the safety rules meet at the same pitch: 4/12 is where asphalt shingles stop needing double underlayment and where OSHA’s steep-roof rules begin.
Roof pitch FAQ
What is the minimum pitch for 3-tab shingles?
The same as for any asphalt shingle: 2 in 12 under the 2021 IRC, with double underlayment from 2 in 12 up to 4 in 12. The code sets one rule for asphalt shingles, 3-tab and architectural alike.
What is the minimum pitch for roll roofing?
Mineral-surfaced roll roofing may not go on slopes below 1 in 12, about 4.8°, under IRC Section R905.5.2.
What is the minimum pitch for cedar shingles?
3 in 12 for wood shingles and 3 in 12 for wood shakes under the 2021 IRC, which is about 14.0°.
Sources & method
Angles are arctan(rise ÷ 12) and percent slopes rise ÷ 12 × 100. Minimum slopes are from the 2021 International Residential Code, Section R905; low-slope and steep definitions and the fall-protection rule from OSHA; the traditional pitch from Swanson Tool’s rafter handbook.
- International Code Council. 2021 IRC Chapter 9 Roof Assemblies, Section R905 Requirements for Roof Coverings. 2021 IRC
- U.S. Department of Labor, Occupational Safety and Health Administration. 29 CFR 1926.500(b) Definitions (Subpart M, Fall Protection). 29 CFR Part 1926 Subpart M, current text on osha.gov
- U.S. Department of Labor, Occupational Safety and Health Administration. 29 CFR 1926.501(b)(11) Steep roofs. 29 CFR Part 1926 Subpart M, current text on osha.gov
- Swanson Tool Company. Roof Pitch Reference, The Blue Book. page read Nov 14, 2026
- CertainTeed. Landmark Shingles Technical Data Sheet. © 08/24
- Roof Pitch Calculator: Degrees, Slope & Roof HeightFind the pitch from a rise and run, an angle or a building’s width.
- Roof Pitch Chart: Angles in Degrees, Slope & MultiplierDegrees, percent slope and roof-area multiplier for every pitch from 1/12 to 24/12.
- Shingle Calculator: Bundles, Starter & Ridge CapBundles, starter strip and ridge cap for a roof from its size and pitch.
Marko Visic
I'm Marko Visic, a physics graduate who builds data-driven calculators. I run ConstructionCalc through my company, Moving Data Systems d.o.o.
The calculators help you plan a DIY job or check a contractor's quote before you sign. Each one cites its sources and shows its method, and cost figures are computed from public primary data. If a number looks wrong, email info@constructioncalc.org and I'll trace it to its source or fix it.