What may cause first floor gutters to overflow?

The reason that second-floor gutters draining into first-floor gutters can lead to overflow is primarily due to the volume of water being channeled into a system that may not be designed to handle it. When heavy rainfall occurs, or the second-floor gutters experience a significant amount of water runoff, this additional load can exceed the capacity of the first-floor gutters. If these gutters are already managing their own drainage, the influx from the upper level can quickly lead to overflow.

Moreover, first-floor gutters are typically designed to accommodate a certain amount of water based on expected conditions, but the added volume from second-floor gutters can overwhelm them. This is especially true if the first-floor gutters are not adequately sized for increased drainage needs. In contrast, other factors like improper installation or deterioration can lead to a range of issues, but they do not directly relate to the specific scenario of additional water flow from higher levels as the option regarding second-floor drainage does.

By understanding the mechanics of how water drainage systems work, it's clear that the interconnection of gutters across different stories of a building plays a significant role in managing and directing water flow efficiently, and any mismanagement can lead to increased overflow risks.