Calculating the Importance of Gutters and Drainage

What’s the Volume of Water After a Rainstorm?

Let’s start by considering exactly how much water you’ll need to manage after each rainstorm. In this example, we will base our calculations on a 1,600-square-foot single-story home. 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 nearly 1,000 gallons of water.  A hurricane will generate at least six to 12 inches of rainfall, causing almost 12,000 gallons of water to fall 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. 

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 roof’s pitch can also affect how much water you must manage. This is caused by 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 sloped at a 45-degree angle (otherwise known as a 12×12) will accumulate 30 percent more rain than standard measurements. The roof pitch factor for this slope is 1.3. 

In the scenario above, if one inch of rain falls on a home with a steeply pitched roof, 1,296 gallons instead of 997 gallons will fall on it. 

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 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. 

Factors To Consider To Properly Size Gutters 

• 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

Note: the average rainfall of Virginia is 43”.

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 below the surface could flow back toward your foundation because of the clay bowl effect. 

Underground water flow is usually determined when a home is built. The soil excavated for a foundation will have different drainage properties when 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, your home will likely experience water issues. It could begin with dampness and humidity. Then, water will start to seep through joints and crevices, eventually accumulating 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 could cost $25,000.

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 preventive water management has clear advantages. In addition to properly sized gutters, many homes can benefit from additional drainage solutions, including professional gutter cleaning, basement waterproofing, or crawl space encapsulation.

A reliable sump pump is one solution that should be included in any waterproofing system. Sump pumps benefit homes with any 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 installing 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 to protect your home from water damage.

Foundation Waterproofing FAQs

Is DIY crawl space waterproofing advisable?

We strongly advise against attempting to waterproof or repair your crawl space on your own. The crawl space can be a dangerous area, and temporary solutions from hardware stores are insufficient. Trust the experienced professionals at JES Foundation Repair for a thorough inspection and customized waterproofing solutions. Contact us to learn more and schedule a free inspection.

What are the costs involved in crawl space waterproofing? 

The cost varies depending on your crawl space size and the extent of repairs needed. Schedule a free inspection with a JES Foundation Repair specialist for a detailed cost analysis. We offer no-obligation estimates and financing options.

Should I Waterproof My Crawl Space?

The average crawl space in Northern Virginia is somewhat of a contradiction. While a property’s crawl space is undeniably one of the most vulnerable parts of the structure as a whole, it is also one of the most important. As well as providing a buffer zone between your main home and the ground, your crawl space acts as a hub for your property’s utilities. Pipes, wires, and your HVAC ducts can all be found in this space.

As such, it is ironic and somewhat surprising that many older homes have next to no waterproofing measures in their crawl space. This can wreak havoc on their pipes, wires, and HVAC system, especially when there is dampness or humidity at work in the space. Older homes, in particular, are vulnerable because of the likelihood that they will have exposed crawl space vents. As such, waterproofing your property’s crawl space is a very good idea if you intend to protect your home from avoidable damage in the long run.

Waterproofing your crawl space will have immediate benefits, of course, like a reduction in the levels of humidity and dampness, but also more indirect benefits. For example, a property with lower levels of humidity will find that their HVAC system can provide results with much less stress and energy consumption. This will lead to lower energy bills in the long run, as well as a generally healthier and more comfortable environment.

Holly Richards-Purpura

Content Writer

Holly is a Content Writer for Groundworks who has written and edited web content for the foundation services industry for 10 years. With a background in journalism, her passion for the written word runs deep. Holly lives in Columbus, OH, with her husband. Along with educating homeowners, she also has a big heart for the Big Apple.