The Amerimax Home Products FLEX Drain Perforated Drain Pipe is able to solve this issue for the low price of $5.97 (for the 8 foot version). We are not being compensated in any way for reviewing this product, and won't receive any kickback if you buy it using that link. We just saw it as a potential solution to one of the most common issues we see on customers' properties.
We purchased one, and put it to the test. Here are the assumptions that formed our test case:
- A 1 in/hr rain rate (towards the higher end, but not the max)
- A roof footprint of 1200 square feet with 4 downspouts
- The downspouts split the total amount of rainfall evenly
After doing some math, these assumptions come out to roughly 12 Liters per minute per downspout. The hose was calibrated to output water at this rate by adjusting the nozzle until it matched that rate. The pipe was set up to have a nice downward slope toward the bucket that would measure the amount of water. It sloped down about 18 inches over the 8 foot length. You can see a picture here:
Of the 12 Liters that went into the entrance of the pipe, 4.8 Liters made it into the bucket, about 40%. The remainder came out pretty evenly across the length of the pipe, except that the first 9 inches or so of the pipe doesn't have any perforations, so none came out in that length. Using that information, we can calculate that approximately 79% of the water made it to at least 3 feet away from the entrance to the pipe.
By adding a 2 foot long splash block underneath the perforated pipe, we can ensure that zero water hits the ground less than 2 feet from the entrance to the pipe. Approximately 13% would hit the ground 2 feet from the foundation at the end of the splash block. 8% would hit the ground between 2 and 3 feet from the foundation, and the remaining 79% would still hit the ground at least 3 feet from the foundation.
The percentage making it to the end of the drain pipe is likely to increase with the buildup of debris in the drain pipe. However, even if this did cause some of the perforations not to drain, the debris itself might prevent standing water from collecting, and the perforations on the sides and top of the pipe would allow evaporation that currently doesn't occur with the standard downspout extenders. If desired, the first 2-3 feet or so could be purposefully sealed or clogged on the perforations along the bottom to ensure no water hits the ground within 3 feet of the foundation. The other perforations on the sides and top should allow enough evaporation to eliminate standing water in the corrugations, and it would still be a lot better than a standard downspout extender.
An added benefit of this drain pipe is that it disperses water over the entire length of the pipe rather than all at one spot. This can help prevent erosion and runoff, helps the water soak into the ground, and promotes a healthy watershed by minimizing runoff.
Overall, we would recommend this product. For anyone that has concerns about a flooded basement due to issues in the past, we'd recommend adding the splash block underneath or purposefully sealing the perforations along the bottom for the first few feet.