5/12 Roof Pitch — Gutter Sizing Guide
A 5/12 pitch provides a moderately sloped appearance that is popular on two-story homes, colonial-style construction, and transitional architectural designs. The pitch factor of 1.08 adds 8 percent to the effective area, which starts to become significant for gutter sizing in areas with high rainfall intensity. Water velocity on a 5/12 roof is noticeably faster than on a 4/12, improving the self-cleaning characteristics of both the roof and the gutters. Most standard roofing materials perform well at this pitch, and the increased attic volume provides better ventilation and potential storage or living space.
5/12 Pitch Specifications
Gutter Sizing Grid for 5/12 Pitch
The table below shows the recommended gutter profile for various combinations of roof area and rainfall intensity at the 5/12 pitch. The pitch factor of 1.08 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" | Half-Round 5" |
| 1,200 sqft | Half-Round 5" | Half-Round 5" | Half-Round 5" | K-Style 5" |
| 1,500 sqft | Half-Round 5" | Half-Round 5" | Box 5" | Half-Round 6" |
| 2,000 sqft | Half-Round 5" | Box 5" | Half-Round 6" | K-Style 7" |
| 2,500 sqft | Half-Round 5" | K-Style 5" | K-Style 7" | K-Style 7" |
| 3,000 sqft | Half-Round 5" | Half-Round 6" | K-Style 7" | 7"+ |
| 4,000 sqft | Box 5" | K-Style 7" | 7"+ | 7"+ |
Effective Area Examples at 5/12
The pitch factor of 1.08 means that every square foot of horizontal roof footprint represents 1.08 square feet of actual roof surface draining to the gutters. Here are common home sizes with the effective drainage area calculated at 5/12 pitch:
| Horizontal Area | Effective Area (5/12) | Increase |
|---|---|---|
| 800 sqft | 864 sqft | +64 sqft |
| 1,000 sqft | 1,080 sqft | +80 sqft |
| 1,200 sqft | 1,296 sqft | +96 sqft |
| 1,500 sqft | 1,620 sqft | +120 sqft |
| 2,000 sqft | 2,160 sqft | +160 sqft |
| 2,500 sqft | 2,700 sqft | +200 sqft |
| 3,000 sqft | 3,240 sqft | +240 sqft |
| 4,000 sqft | 4,320 sqft | +320 sqft |
| 5,000 sqft | 5,400 sqft | +400 sqft |
Installation Considerations for 5/12 Roofs
Standard-slope roofs at 5/12 pitch provide a good balance of water drainage speed and gutter catchment. Water arrives at the gutter at a moderate velocity that cleans debris effectively without risking overshooting. Standard 5-inch or 6-inch gutters with hidden hangers spaced at 24 to 36 inches provide reliable performance. Ensure that drip edges extend properly into the gutter to direct water flow, and maintain adequate gutter slope of at least 1/16 inch per foot toward each downspout. In areas with heavy tree coverage, gutter guards significantly reduce maintenance frequency.
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 5/12 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 + (5/12)2) = 1.083; this calculator rounds that to 1.08. The table that This Old House and many installers use assigns one factor to a whole band of pitches, 1.05 for 5/12. On a 2,000 sq ft footprint the difference is 60 sq ft of effective area, which can be the margin between two gutter sizes in a high-intensity state.
| Method | Factor at 5/12 | 2,000 sq ft footprint becomes | Basis |
|---|---|---|---|
| True surface area | 1.083 | 2,167 sq ft | sqrt(1 + (rise/12)^2), unrounded |
| This calculator | 1.08 | 2,160 sq ft | surface area, rounded to two places |
| Industry table (This Old House) | 1.05 | 2,100 sq ft | one factor per band of pitches |
Roof Covering Rules at 5/12
A 5/12 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, 5/12 is 22.6 degrees. A 30-foot-wide gable at this pitch has its ridge 6.3 feet above the wall plates, and the roof carries 1.08 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 5/12
Dividing a profile's 1 in/hr capacity by the rainfall intensity and this pitch's factor of 1.08 gives the largest horizontal footprint it can serve. The 5-inch K-style, the most common residential gutter, covers 5,111 sq ft of footprint at 1 in/hr on a 5/12 roof but only 1,277 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 | 5,111 sq ft | 6,666 sq ft | 7,370 sq ft | 10,537 sq ft |
| 1.5 in/hr | 3,407 sq ft | 4,444 sq ft | 4,913 sq ft | 7,024 sq ft |
| 2 in/hr | 2,555 sq ft | 3,333 sq ft | 3,685 sq ft | 5,268 sq ft |
| 2.5 in/hr | 2,044 sq ft | 2,666 sq ft | 2,948 sq ft | 4,214 sq ft |
| 3 in/hr | 1,703 sq ft | 2,222 sq ft | 2,456 sq ft | 3,512 sq ft |
| 3.5 in/hr | 1,460 sq ft | 1,904 sq ft | 2,105 sq ft | 3,010 sq ft |
| 4 in/hr | 1,277 sq ft | 1,666 sq ft | 1,842 sq ft | 2,634 sq ft |
| 4.5 in/hr | 1,135 sq ft | 1,481 sq ft | 1,637 sq ft | 2,341 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 5/12 roof?
This calculator uses 1.08, which is the true surface area of a 5/12 roof per square foot of footprint (the hypotenuse, sqrt(1 + (5/12)^2) = 1.083, rounded). The industry table reproduced by This Old House uses 1.05 for this pitch, because it groups pitches into bands. On a 2,000 sq ft footprint the two methods differ by 60 sq ft of effective area; this site's figure is the more conservative one.
Can I use asphalt shingles on a 5/12 roof?
A 5/12 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 5/12?
A 5-inch K-style is rated for 5,520 sq ft of effective roof at 1 in/hr. At 5/12 (factor 1.08) that is a footprint of about 5,111 sq ft at 1 in/hr, 2,044 sq ft at 2.5 in/hr, and 1,277 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 5/12 roof in degrees?
5/12 is 22.6 degrees from horizontal. On a 30-foot-wide gable the ridge sits 6.3 feet above the top of the walls, and each square foot of attic footprint carries 1.08 square feet of roofing. Roofers can generally walk this pitch, which keeps gutter installation labor in the normal range.
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