Installation Details · FAQ

What gutter size handles Illinois rainfall?

5-inch gutters with 2×3 inch downspouts are the Illinois standard and handle the rainfall on roughly 80% of Madison County homes. Larger roofs (3,000+ square feet) or roofs with significant slope concentration toward one corner benefit from 6-inch gutters with 3×4 downspouts, which carry 40% more water.

The other factor is downspout count. Trill’s general rule: one downspout per 35 to 40 feet of gutter run, with downspouts at the lowest points. Most Illinois homes have one or two too few downspouts, which is why you’ll see gutters overflowing in heavy rain even when the gutters themselves are sized correctly. Add a downspout where water concentrates and the overflow stops.