The rule of thumb for downspouts is at least one downspout for each _____ feet of gutter.

The guideline for installing downspouts suggests that there should be at least one downspout for every 40 feet of gutter installed. This practice ensures that rainwater is effectively channeled away from the roof and foundation of a structure, reducing the risk of water damage and erosion.

When gutters are overloaded due to insufficient downspouting, they can overflow, leading to water pooling around the foundation, which might cause long-term structural issues. By adhering to this rule, homeowners and builders can help ensure proper drainage and maintenance of the property.

The other options represent distances that are too short or too long for ideal drainage practice. For instance, having one downspout for every 20, 30, or 50 feet may not provide the same level of efficiency in water drainage, which is crucial in preventing water-related damages. Thus, maintaining the standard of one downspout for every 40 feet of gutter is essential for optimal drainage performance.