Calculating the Importance of Gutters and Drainage

We did the math to find out exactly how important gutters and drainage are to your home's water management.

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Gutters and drainage are not the only tools you need for home water management. However, these systems can be the first line of defense for keeping thousands of gallons of water out of your basement or crawl space. 

By analyzing weather and hydrology, combined with math calculations and soil science, we’re able to calculate exactly how important gutters and drainage is to your home’s water management system. 

What’s the Volume of Water After a Rainstorm?

Let’s start by considering exactly how much water you’ll be managing after each rainstorm. Let’s use a 1,600-square-foot single-story home in this example. However, a larger footprint will accumulate more water on the roof, and a smaller footprint will mean less water falls on the roof.

Just one inch of rainfall on this 1,600-square-foot area will accumulate to nearly 1,000 gallons of water. As we look at bigger rainstorms such as a hurricane where a foot of rain falls, you could have nearly 12,000 gallons of water falling on your roof. 

When dealing with such a large volume of water, it becomes increasingly important to direct that water away from your foundation and keep it out of your basement or crawl space.

how many gallons of water after rainfall

Rainfall on a 1,600-square-foot home

  • 1″ of rain: 997 gallons of water
  • 5″ of rain: 4,984 gallons of water
  • 12″ of rain: 11,962 gallons of water

How Does Your Roofline Affect Water Volume?

The baseline calculations above only consider the amount of rain and the size of the home. However, the pitch of your roof can also affect how much water you’ll have to manage. This is because of the wind. 

It’s unlikely that raindrops fall straight downward. Instead, wind can blow raindrops while they’re falling, creating a diagonal trajectory. If a roof has a steeper pitch, it’ll catch more rain because of how the wind blows into it. Conversely, a flatter roof will see less of an impact of wind on total rain accumulation. 

The rule of thumb is that roofs that are sloped at a 45-degree angle (otherwise known as a 12×12) will have 30 percent more rain accumulation than standard measurements. The roof pitch factor for this slope is 1.3. 

In the case of the one inch of rain in the scenario above, a home with a steeply pitched roof could have 1,296 gallons of rain falling on it instead of 997 gallons. 

What’s Included in Drainage and Gutter Calculations?

Your home’s drainage capacity must be sized for the maximum rainfall intensity at your location. For example, homes in a dry part of the country would require less drainage capacity than homes in the Richmond, VA, area. 

If gutters and drainage systems are undersized, water will overflow your gutters and fall directly next to your home foundation. Over time, this water stress can cause foundation cracks. Overflowing gutters can also cause your home to flood because water is directed toward your home instead of away from it. 

Calculations to properly size gutters must consider: 

  • Home square footage
  • Roof pitch
  • Maximum rainfall intensity of your location
  • Shape of gutters (K-style or half-round)
  • Gutter dimensions
  • Gutter slope
  • Number of downspouts

How Does Your Soil Affect Your Home’s Drainage?

Gutters, extension pipes, and surface drainage are only the visible part of your home’s water management system. The soil below the surface also affects how water flows on your property. For example, even when the terrain is carrying surface water away from your house, groundwater that’s below the surface could be flowing back toward your foundation because of the clay bowl effect. 

Underground water flow is usually determined when a home is built. The soil that’s excavated for a foundation will have different drainage properties when it’s backfilled. As a result, groundwater could remain trapped in the soil around the home. This pervasive soil saturation then leads to a buildup of hydrostatic pressure against your foundation and can cause basement or crawl space flooding if left unresolved. 

How Much Does a Home Flood Cost?

Without functional gutters, drainage, and waterproofing, you will likely start to develop water issues. It could start as dampness and humidity. Then water will start to seep through joints and crevices. Eventually, you could have inches of water in your home. 

If one inch of rain can yield 997 gallons of water, a home flood can quickly become an expensive nightmare. FEMA estimates that the repair costs after one inch of water enters the home would top $25,000.

cost of water damage, repairs and flood cleanup

Cost of Water Damage and Repairs

(2,500-square-foot single-story home)

  • 1 inch of water in the home: $26,807
  • 1 foot of water in the home: $72,163 
  • Damaged foundation: Lose up to 30% of your home value.
    That’s $105,000 for a $350,000 home.

The cost of flood cleanup demonstrates that there are clear advantages to preventative water management. In addition to properly sized gutters, many homes can benefit from additional drainage solutions, basement waterproofing, or crawl space encapsulation

One solution in particular that should be included in any waterproofing system is a reliable sump pump. Sump pumps benefit homes with any kind of water seepage issues, and they are even more important for homeowners with increased flood risk so they’re prepared for extreme weather events that overwhelm drainage systems. Some flood insurance policies will even contribute $1,000 toward the installation of sump pumps to mitigate flood loss. 
If you’re concerned about your foundation and waterproofing measures, get a free inspection from JES Foundation Repair to learn how you can protect your home from water damage.

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