How Much of a Slope Do You Put in House Gutters?

Proper Pitch

• The proper slope for gutters is between 1/4 and 1/2 inch per 10 foot run. So, a gutter that spans 30 feet needs to slope 3/4 to 1 1/2 inches from its highest point to its lowest point along the home’s fascia board. That’s just enough of an angle to allow gravity to draw the water toward a downspout, which is placed at the lowest end of the slope. The high point of the gutter is typically about 1/2 inch or so below the roof line.

Long Gutters

• Some homes need long gutter runs to span a long outside wall. Gutters that extend 40 feet or more need a high point in the center of the run, with 1/4 to 1/2 inch slopes in either direction from that center point. An alternative is to slope the gutter toward the center from each end. That configuration requires the downspout to be placed in the center of the gutter run rather than at the ends of the run.

New Installations

• To establish the proper pitch on a new gutter installation, make sure the roof line is level. If it is, place a nail at the high end of the gutter. If it isn’t, draw a level line across the fascia board, then place a nail at the high side. Calculate how far down the low end needs to be to achieve a 1/4 to 1/2 inch slope. Measure that amount down from the level line or roof line and place a nail there. Snap a chalk line between the two points to establish a reference line.

Existing Gutters

• Run water from a garden house into the gutter. If it drains out without pooling inside the gutter, the slope is correct. If pooling occurs, you can adjust the gutter slope by gently bending the nails that hold the existing gutter in place. Bending nails this way also removes any low spots that may tend to collect and hold water inside the gutter. Water that fails to drain can corrode the gutter and cause it to leak.