Gutter slope
By Gutter Report Editorial. Last reviewed August 2026. How we research this.
In brief
Aim for about 1/2 inch of fall per 10 feet, running toward the downspout. That sits in the middle of four published standards that disagree by two and a half times: This Old House and Modernize say 1/4 inch per 10 feet, Engineering LibreTexts says 1/2 inch, and Texas A&M AgriLife Extension and Fine Homebuilding call for 1/16 inch per foot, which is 5/8 inch per 10 feet. Slope is not just about draining. It is a capacity input: pitching a gutter at 1/8 inch per foot multiplies the roof area it can drain by 1.4, per Fine Homebuilding. But Berger sets a floor. A gutter pitched at 1/16 inch per foot or less counts as a level gutter, so a token slope earns nothing. What matters more than the number is that the fall is continuous, with no low spot in the middle.
1.0Four standards, side by side
| Source | As published | Per 10 feet | On a 40 ft run |
|---|---|---|---|
| IN | IN | ||
| This Old House, Modernize | 1/4 in. per 10 ft | 0.25 | 1.0 |
| Fine Homebuilding, minimum | 1/2 in. in 20 ft | 0.25 | 1.0 |
| Engineering LibreTexts | 1/2 in. per 10 ft | 0.50 | 2.0 |
| Texas A&M AgriLife Extension | 1/16 in. per foot | 0.63 | 2.5 |
| Fine Homebuilding, ideal | 1 in. per 16 ft | 0.63 | 2.5 |
| Berger | 1/16 in. or greater per foot | 0.63 or more | 2.5 or more |
| CDA, architectural copper | Not less than 1/8 in. per foot | 1.25 | 5.0 |
The per 10 feet and 40 foot columns are our arithmetic on each published figure. Note the pattern: the consumer publishers cluster at the shallow end and the trade and specification sources sit at the steep end. Fine Homebuilding gives both, calling 1 inch per 16 feet the ideal and 1/2 inch in 20 feet the minimum that will still drain.
The Copper Development Association figure is five times the This Old House one, and it is written for built up architectural copper rather than a tract house, so read it as the ceiling rather than a residential target. Its logic is worth borrowing though: a trough that holds standing water is a liner that fails early.
2.0Slope is a capacity input
This is the part treated as a detail and is not one. More fall means faster flow, which means the same gutter carries more roof.
| Gutter | At 1/16 in. per ft | At 1/8 in. per ft | Gain |
|---|---|---|---|
| GPM | GPM | PERCENT | |
| 8 in. semicircular | 172 | 247 | 44 |
| 10 in. semicircular | 331 | 472 | 43 |
Those capacities are International Plumbing Code Table 1106.6. The gain column is our arithmetic. Doubling the slope adds a bit over 40 percent of capacity, which lines up independently with Fine Homebuilding's statement that pitching at 1/8 inch per foot multiplies the drainable roof area by 1.4.
Set that against the alternatives. Adding a second downspout doubles capacity. Stepping a 5 inch gutter up to 6 inch buys about 40 percent, per Englert. So correcting the slope on a badly hung run buys roughly what a whole size increase buys, at the price of a few hangers.
And the floor that makes it real: Berger states that the capacity of a gutter with 1/16 inch per foot of pitch or less is taken as that of a level gutter, even though it is somewhat greater. Below that line, you get no credit.
3.0The level gutter, which is a real option
On a long front elevation, a gutter that visibly falls two inches across the facade reads as crooked against level trim and level windows. Builders know this, and the answer has a name.
Berger states it directly: a gutter can be run level for appearance, but additional downspout will be necessary. That is the whole trade. You give up the pitch credit and buy the capacity back with more outlets. See how many downspouts.
A second approach is to pitch from the middle outward to an outlet at each end. A 40 foot run then needs only 20 feet of fall in each direction, so at 1/4 inch per 10 feet the visible drop is half an inch rather than an inch. This Old House notes that when you add a second outlet, the gutter should be pitched so water runs toward both.
4.0How to check the slope on your house
- Find the outlet. The gutter should fall toward it. If there are two, the high point is between them.
- Run a string. Tie a string along the front lip from the high end to the outlet, pull it tight, and level it with a line level.
- Measure the gap at the low end. That gap is the total fall. On 40 feet, expect about 1 inch at the shallow standard and about 2.5 inches at the steep one.
- Check the middle. This matters more than the total. Measure the gap at several points along the run. It should grow steadily. If it grows and then shrinks, there is a low spot.
- Look after rain. Standing water in a dry hour is the simplest proof of a low spot, and it does not need a ladder if you can see the trough from a window or a slope.
A low spot is the most common real slope fault, and it is not a slope number problem. It is a hanger that let go, or fascia that sagged behind it. HomeGuide prices re-sloping or realigning a run at $75 to $200, and re-hanging a sagging section at $75 to $300.
Where the gutter sits relative to the roof edge
Slope is one of two positioning decisions. The other is how far the gutter hangs below the line the roof would follow if it kept going, and it exists so sliding snow and ice clear the gutter instead of tearing it off.
| Roof pitch | Clearance below extended roof line |
|---|---|
| IN | |
| 0 in 12 to 2 in 12 | 1 |
| 3 in 12 to 5 in 12 | 3/4 |
| 6 in 12 to 8 in 12 | 1/2 |
| 9 in 12 or greater | 1/4 |
That table is Berger's. Fine Homebuilding publishes a similar set measured the same way: 3/4 inch below the projected roof plane at 5 in 12, 1/2 inch at 7 in 12, and 1/4 inch at 12 in 12. The two agree closely.
There is also a front to back rule. Texas A&M says keep the front of the gutter 1/2 inch lower than the back so water does not splash against the building. Fine Homebuilding says about 1 inch, twice as much. Either way, the front lip is the low edge, so overflow goes outward rather than into the fascia.
5.0You may not have a slope problem
Slope gets blamed for a lot of overflow that is not its fault. Before you pay anyone to re-hang a run, rule out the two cheaper causes.
A clog backs water up at any slope, and it is the first thing to check. Too few downspouts floods a correctly pitched gutter in a hard rain, and that is a capacity problem rather than a fall problem. Both are covered on how many downspouts.
Water appearing behind the gutter rather than over the front is not slope at all. That is usually the drip edge, or a built-in gutter whose liner has failed, and no amount of re-pitching will touch it.
We can say all of this plainly because we do not sell gutters and we do not install them. If the run really is hung wrong, a repair at a national average of $275 covers it, and repair or replace works through the rest.
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Common questions
How much slope should a gutter have?
The published standards disagree by two and a half times. This Old House and Modernize call 1/4 inch per 10 feet standard. Engineering LibreTexts gives 1/2 inch per 10 feet. Texas A&M AgriLife Extension and Fine Homebuilding call for 1/16 inch per foot, which is 5/8 inch per 10 feet. Berger says pitch 1/16 inch or greater per foot. Use 1/2 inch per 10 feet as a working target, and never accept a low spot.
Does gutter slope affect how much water it carries?
Yes, substantially. Fine Homebuilding states that pitching a gutter at 1/8 inch per foot multiplies the roof area it can drain by 1.4. The plumbing code table shows the same effect: an 8 inch semicircular gutter carries 172 gallons a minute at 1/16 inch per foot and 247 at 1/8, which is about 43 percent more.
Is there a minimum slope below which it does not count?
Yes, and it is a useful line. Berger states that the capacity of a gutter pitched at 1/16 inch per foot or less is taken as that of a level gutter, even though it is somewhat greater. So a token slope buys no capacity credit. If you want the capacity, you need real fall.
Can gutters be installed level?
Yes, and it is a legitimate choice on a long visible elevation where a sloping gutter line would look wrong against level trim. Berger says gutters can be run level for appearance, but additional downspout will be necessary. That is the trade: you buy back the lost capacity with more outlets.
How do I check my gutter slope?
Run a string line from the high end to the outlet along the front lip, pull it tight and level, and measure the gap at the outlet end. On a 40 foot run at 1/4 inch per 10 feet you should find about 1 inch of fall. What matters even more is that the fall is continuous. A run that falls, rises and falls again holds water in the middle, and that low spot is where it will spill.
How far below the roof edge should the gutter sit?
It depends on the roof pitch, because snow and ice have to slide clear. Berger publishes a table: 1 inch of clearance below the extended roof line for a 0 to 2 in 12 roof, 3/4 inch for 3 to 5 in 12, 1/2 inch for 6 to 8 in 12, and 1/4 inch for 9 in 12 or steeper. Steeper roofs need less clearance.
- Rev
- RevAugust 2026
- Source
- SourceThis Old House, Modernize, Texas A&M, Fine Homebuilding, Berger, CDA, IPC via UpCodes (read 2026-08-21)