Short Answer
They can overflow during heavy rainfall.
Detailed Explanation
Gutters are sized based on the roof area they drain and the expected rainfall intensity. If gutters are too small for the roof area, they can't handle the volume of water during heavy rain, causing overflow. Overflowing gutters defeat the purpose of having gutters — the water falls directly next to the foundation instead of being directed away. In South Jersey, where heavy thunderstorms can produce significant rainfall in short periods, undersized gutters are a common problem. The solution is to install gutters with adequate capacity (typically 5-inch or 6-inch gutters, depending on roof area) and ensure proper slope toward downspouts for efficient drainage.
Why It Matters
Undersized gutters can cause the same foundation and water damage as having no gutters at all, because overflow defeats the gutter system.
When Repair Makes Sense
Existing gutters are the right size but are clogged or improperly sloped, causing overflow.
When Replacement Makes Sense
Existing gutters are undersized for the roof area and can't handle heavy rainfall even when clean.