If your gutters overflow during a heavy rain, either the gutters and/or downspouts are clogged, the gutters are sagging and thereby preventing water from reaching the downspouts, or the gutters and downspouts are not large enough to handle the volume of rain runoff.

In most cases, gutters overflow because leaves and debris clog them, essentially creating dams that prevent water from flowing through them to the outlets above the downspouts. In fact, these clogs often occur right at the outlets. When this is the case, it is time to clean out the gutters. For more about this, please see How to Clean Rain Gutters.

Gutters that sag are a different issue--and the more they fill up with water, the more they are likely to sag because they become so heavy when full. Please see How to Fix Sagging Rain Gutters.

If the gutters overflow but are not sagging or clogged up, you will probably need to install new, larger downspouts and gutters to solve the problem.