11/12 Roof Pitch — Gutter Sizing Guide
An 11/12 pitch is extremely steep, approaching the 45-degree angle of a 12/12 pitch. The pitch factor of 1.36 adds 36 percent to the effective area, creating a drainage challenge that requires careful gutter sizing and downspout planning. Water cascades off an 11/12 roof with high velocity, and wide gutters with extended gutter aprons are necessary to prevent overshooting. This pitch is rare in standard residential construction but appears on decorative gables, dormers, turrets, and Gothic-influenced architecture. The extreme slope means that snow and ice rarely accumulate, sliding off immediately, which can be both an advantage and a hazard.
11/12 Pitch Specifications
Gutter Sizing Grid for 11/12 Pitch
The table below shows the recommended gutter profile for various combinations of roof area and rainfall intensity at the 11/12 pitch. The pitch factor of 1.36 is applied to the horizontal roof area before multiplying by the rainfall intensity. This grid helps you quickly find the recommended gutter size without running a custom calculation. For roof areas or rainfall intensities not shown, use the gutter size calculator for a precise recommendation.
| Roof Area | 1 in/hr | 2 in/hr | 3 in/hr | 4 in/hr |
|---|---|---|---|---|
| 800 sqft | Half-Round 5" | Half-Round 5" | Half-Round 5" | Box 5" |
| 1,200 sqft | Half-Round 5" | Half-Round 5" | Box 5" | Half-Round 6" |
| 1,500 sqft | Half-Round 5" | Box 5" | Half-Round 6" | K-Style 7" |
| 2,000 sqft | Half-Round 5" | K-Style 5" | K-Style 7" | K-Style 7" |
| 2,500 sqft | Half-Round 5" | Half-Round 6" | K-Style 7" | 7"+ |
| 3,000 sqft | Box 5" | K-Style 7" | 7"+ | 7"+ |
| 4,000 sqft | K-Style 5" | K-Style 7" | 7"+ | 7"+ |
Effective Area Examples at 11/12
The pitch factor of 1.36 means that every square foot of horizontal roof footprint represents 1.36 square feet of actual roof surface draining to the gutters. Here are common home sizes with the effective drainage area calculated at 11/12 pitch:
| Horizontal Area | Effective Area (11/12) | Increase |
|---|---|---|
| 800 sqft | 1,088 sqft | +288 sqft |
| 1,000 sqft | 1,360 sqft | +360 sqft |
| 1,200 sqft | 1,632 sqft | +432 sqft |
| 1,500 sqft | 2,040 sqft | +540 sqft |
| 2,000 sqft | 2,720 sqft | +720 sqft |
| 2,500 sqft | 3,400 sqft | +900 sqft |
| 3,000 sqft | 4,080 sqft | +1,080 sqft |
| 4,000 sqft | 5,440 sqft | +1,440 sqft |
| 5,000 sqft | 6,800 sqft | +1,800 sqft |
Installation Considerations for 11/12 Roofs
Very steep roofs at 11/12 pitch present the most challenging gutter sizing scenario. The 36 percent increase in effective area combined with extreme water velocity requires careful attention to both gutter size and placement. Six-inch gutters are the absolute minimum, and 7-inch commercial profiles should be considered for larger roof sections. Extended gutter aprons are essential to prevent overshooting, and gutter mounting hardware must be exceptionally robust to withstand the forces of sliding snow and ice. Professional installation with engineered mounting details is strongly recommended for roofs at this pitch.
Regardless of pitch, proper gutter maintenance is essential for long-term performance. Inspect gutters at least twice per year, checking for proper slope, secure mounting, clear downspouts, and intact seals at joints and corners. After heavy storms, verify that no debris blockages have formed and that all downspouts are flowing freely. Investing in quality gutter guards rated for your specific gutter profile can dramatically reduce maintenance frequency while ensuring that your gutters remain at full capacity during the storms when they are needed most.
Three Ways to Count a 11/12 Roof
A sloped roof has more surface than the footprint under it, and every sizing method multiplies the footprint by a pitch factor to account for it. The factors disagree. The geometric answer is the hypotenuse, sqrt(1 + (11/12)2) = 1.357; this calculator rounds that to 1.36. The table that This Old House and many installers use assigns one factor to a whole band of pitches, 1.2 for 11/12. On a 2,000 sq ft footprint the difference is 320 sq ft of effective area, which can be the margin between two gutter sizes in a high-intensity state.
| Method | Factor at 11/12 | 2,000 sq ft footprint becomes | Basis |
|---|---|---|---|
| True surface area | 1.357 | 2,713 sq ft | sqrt(1 + (rise/12)^2), unrounded |
| This calculator | 1.36 | 2,720 sq ft | surface area, rounded to two places |
| Industry table (This Old House) | 1.20 | 2,400 sq ft | one factor per band of pitches |
Roof Covering Rules at 11/12
A 11/12 roof clears the IRC Section R905.2.2 thresholds for asphalt shingles (minimum 2:12; double underlayment required below 4:12), so single-layer underlayment is the code minimum and every common roof covering is available. Water leaves the eave faster as pitch rises, which is why steep roofs need the gutter's front lip set low enough, or a drip edge extended, to catch the sheet of water rather than let it overshoot.
For scale, 11/12 is 42.5 degrees. A 30-foot-wide gable at this pitch has its ridge 13.8 feet above the wall plates, and the roof carries 1.36 square feet of covering for every square foot of footprint, which is the same multiplier the gutters see in runoff.
Where Each Gutter Tops Out at 11/12
Dividing a profile's 1 in/hr capacity by the rainfall intensity and this pitch's factor of 1.36 gives the largest horizontal footprint it can serve. The 5-inch K-style, the most common residential gutter, covers 4,058 sq ft of footprint at 1 in/hr on a 11/12 roof but only 1,014 sq ft at 4 in/hr. Look up your state's design intensity on the state pages and read across.
| Intensity | K-Style 5" | Half-Round 6" | K-Style 6" | K-Style 7" |
|---|---|---|---|---|
| 1 in/hr | 4,058 sq ft | 5,294 sq ft | 5,852 sq ft | 8,367 sq ft |
| 1.5 in/hr | 2,705 sq ft | 3,529 sq ft | 3,901 sq ft | 5,578 sq ft |
| 2 in/hr | 2,029 sq ft | 2,647 sq ft | 2,926 sq ft | 4,183 sq ft |
| 2.5 in/hr | 1,623 sq ft | 2,117 sq ft | 2,341 sq ft | 3,347 sq ft |
| 3 in/hr | 1,352 sq ft | 1,764 sq ft | 1,950 sq ft | 2,789 sq ft |
| 3.5 in/hr | 1,159 sq ft | 1,512 sq ft | 1,672 sq ft | 2,390 sq ft |
| 4 in/hr | 1,014 sq ft | 1,323 sq ft | 1,463 sq ft | 2,091 sq ft |
| 4.5 in/hr | 901 sq ft | 1,176 sq ft | 1,300 sq ft | 1,859 sq ft |
All Roof Pitches
Browse gutter sizing guides for other roof pitches. Each pitch page includes sizing grids, effective area calculations, and installation guidance specific to that slope.
How This Guide Works
- Pitch factor here is the roof's true surface multiplier, sqrt(1 + (rise/12)2), rounded to two places; the industry band table is shown for comparison. Effective area = footprint x factor; adjusted area = effective area x rainfall intensity; the recommended gutter is the smallest profile whose 1 in/hr capacity meets the adjusted area.
- Rainfall intensities in the grids are illustrative; state pages carry a statewide 1-hour, 10-year value. SMACNA and Fine Homebuilding size to the 5-minute, 10-year burst, which is higher.
- Roof covering slope limits are from IRC Section R905.2.2 as reprinted by the City of Hopkins, MN: asphalt shingles only at 2:12 or steeper, double underlayment from 2:12 to 4:12. Your jurisdiction's adopted edition governs.
- Sources: Fine Homebuilding #125, Sizing Gutter Systems (capacity and downspout rules); This Old House, How To Size Gutters and Downspouts (pitch-factor table, downspout spacing); the SMACNA Downspout & Gutter Sizing Calculator, built on the Architectural Sheet Metal Manual; NOAA's Precipitation Frequency Data Server (Atlas 14) for point rainfall intensities.
Frequently Asked Questions
What is the pitch factor for a 11/12 roof?
This calculator uses 1.36, which is the true surface area of a 11/12 roof per square foot of footprint (the hypotenuse, sqrt(1 + (11/12)^2) = 1.357, rounded). The industry table reproduced by This Old House uses 1.2 for this pitch, because it groups pitches into bands. On a 2,000 sq ft footprint the two methods differ by 320 sq ft of effective area; this site's figure is the more conservative one.
Can I use asphalt shingles on a 11/12 roof?
A 11/12 roof clears the IRC Section R905.2.2 thresholds for asphalt shingles (minimum 2:12; double underlayment required below 4:12), so single-layer underlayment is the code minimum and every common roof covering is available. Water leaves the eave faster as pitch rises, which is why steep roofs need the gutter's front lip set low enough, or a drip edge extended, to catch the sheet of water rather than let it overshoot.
What is the largest roof a 5-inch K-style gutter can handle at 11/12?
A 5-inch K-style is rated for 5,520 sq ft of effective roof at 1 in/hr. At 11/12 (factor 1.36) that is a footprint of about 4,058 sq ft at 1 in/hr, 1,623 sq ft at 2.5 in/hr, and 1,014 sq ft at 4 in/hr. Find your state's design intensity on the state pages, and move to 6-inch K-style (7,960 sq ft) when the footprint approaches those ceilings.
How steep is a 11/12 roof in degrees?
11/12 is 42.5 degrees from horizontal. On a 30-foot-wide gable the ridge sits 13.8 feet above the top of the walls, and each square foot of attic footprint carries 1.36 square feet of roofing. Roofs this steep are not walkable without staging or fall protection, which adds to gutter installation cost.
Gutter Products and Installation
Quality materials for your gutter project.
Some links above are affiliate links — if you buy through them we may earn a small commission at no extra cost to you. As an Amazon Associate we earn from qualifying purchases.