Calculations for Gutters and Drainage in Central Missouri

Gutters 101

A downspout is a long vertical drainage pipe that goes from the gutters of your home to the ground. It takes rainwater or melting snow that collects in your gutters and channels it downwards along the sides of your home. The bottom part of the downspout is typically angled out several inches to get the water far and away from the building’s foundation.

Types of Gutter Systems

Gutter systems are available in different shapes, sizes, materials, and prices to suit your needs. Here are the three common styles:

What Are Gutters Made Of?

Modern gutters are made from different materials. Let’s look at them briefly.

• Aluminum: This is a popular gutter material because it’s lightweight and easy to install. Aluminum gutters are rust-resistant too, which makes them suitable for areas with constant downpours and snow. They’re also weatherproof, available in many colors, can be painted, and have a lifespan of up to 25 years.
• Steel: It is a durable and rust-resistant material. On the downside, steel is heavy and expensive.
• Vinyl: Another popular option is Vinyl, a lightweight and affordable guttering material. The only problem with it is that it tends to fade when exposed to strong sunlight.
• Zinc: Similar to copper, zinc is hard-wearing and is adaptable to a range of roof configurations as well as architectural styles. However, it’s expensive.

Rainfall and Drainage — Protecting Your Home’s Foundation

Back to our original question… here’s the starting list of what to consider when calculating gutters, downspouts, and overall drainage around your home.

Rooftop Rainfall Accumulation

The example below shows the amount of rainfall that builds up on a 1,600-square-foot single-story home. With just one inch of rainfall, nearly 1,000 gallons of water are looking for somewhere to go once they leave your roof. Add four more inches, and it’s almost 5,000 gallons.

Roof Structure and Water Volume

Drainage Calculation for St. Louis

The NOAA Weather Service estimates that St. Louis’s expected five-minute burst of rain over a 10-year period is 0.623 inches. Calculating inches per hour is 0.623 x 12, which is 7.48 inches.                                                               

For a home of 850 square feet with a roof pitch of 9-in-12 (pitch factor 1.2), the roof watershed is 850 x 1.2, or 1,020 square feet. Multiplying by the rainfall intensity of 7.48 inches yields a drainage capacity of 7,629 square feet.

That barely fits within the capacity of a six-inch K-style gutter at 7,960 square feet. To move water more quickly, the slope of the gutters could be increased, as could the number of downspouts. 

Drainage on the Ground

Rainfall accumulates on the roof as well as on the ground. So all that water moving across the roof (and into the gutters and downspouts) meets up with quite a few more gallons of water that took the direct route to the ground.

All that results in water above ground and water under the ground. The above-ground water ideally will be flowing away from the foundation in response to landscape grading as well as downspout extensions. The underground water will be moving in the opposite direction toward your basement or crawl space.

This happens due to the clay bowl effect. During home construction, the soil was excavated and backfilled once the foundation was built. This disturbed soil has a different drainage factor and will result in water moving toward the foundation, seeking out any cracks or porous concrete, causing flooding. 

To prepare for this, you’ll need to consider basement waterproofing or crawl space encapsulation, both of which can include interior drainage systems and sump pumps.

The Costs of Home Flooding

FEMA has developed cost estimates on the impact of several different levels of home flooding. We’ve highlighted those in the graph below.

You can readily see that taking steps now to prevent water damage can pay off when those storms send water rushing through gutters and downspouts, threatening your foundation.

Ensure Your Home with Expert Gutter Installation

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FAQs

How long does it take for gutters to rust?

It depends on several factors discussed on this page, including: 

• How much water comes into contact with the gutters 
• The presence of dirt and debris 
• Pest damage 

Most gutters can last 20 years or more, but if they have to contend with various problems, they will quickly begin to sustain damage like rust. 

Can clogged gutters attract pests?

Absolutely. Clogged gutters are the ideal location for pests to make their homes. From wasps to birds to squirrels and mice, wet, damp leaves and debris are a hotbed for infestations. 

When should you replace your gutters?

You should replace gutters that are rotting, peeling, cracking, or covered with mildew. All of these are signs that your gutters are failing or close to failing completely.  

Leah Leitow

Content Writer

Leah is a Content Writer for Groundworks with nearly ten years of experience working in the foundation repair industry. Her experience ranges from working with homeowners to find the right solution to training inspectors and staff. In her background as a Michigan journalist, she gained invaluable insight into people's lives throughout our state. Leah lives in metro Detroit with her husband and two sons.