Gutters Overflow in Heavy Rainfall

You clean the gutters twice a year without fail. You’ve checked the gutter channel and downspouts for any blockages. But every time there’s a heavy rainfall, water spills over the gutter section. If debris build-up isn’t the reason, why do the gutters overflow every time it rains heavily? The three most likely causes are improper pitch, an insufficient number of downspouts and incorrect gutter size.


If the gutter system is free of clumps of debris and rainwater still spills over the sides of the gutters, check for standing water. Standing water in the gutter channel might be an indication that the gutters have become misaligned or were not properly pitched to begin with. In order for water to flow through the system properly, gutters should gently slope downwards in the direction of the downpipes. Another indicator of improper pitch is water escaping over the top only at the back of the gutter.

More than One Downspout

However, when water overflows consistently over the front edge of the gutter section, it could be a sign that more downspouts are needed. It’s understandable that one might not be enough, but don’t assume that if there are two downpipes, you don’t need to add any more. The simple rule of one downspout for every 40 feet of gutter might not be sufficient if the roof has multiple levels, is more than two storeys, or the roof configuration is complex.


For most residential applications, the standard 5” gutter is adequate for homes in the Lower Mainland. However, gutters on older or heritage homes might be smaller, and therefore unable to handle a heavy rainfall. Larger homes (with larger roofs) that currently have the standard gutter size installed might function better with 6” gutters.