I'm assuming if you are reading this that you are in an area where is rains quite frequently. I lived in Colorado for 18 years and never even thought about my gutters except for cleaning them out once every couple years. But when I moved to Western Kentucky, where it rains constantly, that changed very quickly. Not only do I have to clean my gutters out every few weeks it seems, but then I realized you also need to make sure the water has a place to go away from the foundation so you don't cause any issues in your foundation. Let's talk about what kind of issues you can run into without extending your gutter downspouts and what the best process is for extending your gutter drainage.
The first and most common problem with not extending your gutter downspouts is that you are dumping hundreds to thousands of gallons of water right next to your foundation. Think about this: If you have a 1,500 sqft roof and it rains one inch, that means you have around 1,000 gallons of water coming out of your gutters. If you have a basement or crawl space, that water will most likely infiltrate through small cracks and imperfections in your foundation. The last thing you want is water in your basement or crawl space.
Another problem with letting your gutters drain next to your foundation is something called hydrostatic pressure, which basically means; -I'm no scientist mind you- the added water in the soil makes the ground expand which pushes on your foundation and since there is nothing on the other side of the foundation to push back it can cause damage to or shift your foundation wall. This is obviously very bad for you and your wallet.
One last problem is more of an aesthetic issue in regards to taking caring of your nice, neat landscape. Dumping that much water in your flower bed can drown your flowers. It can also wash out areas of landscape or at a very least leave a big divot, or big mud pit, where the water hits the ground constantly.
Okay, now we know why we need to extend the gutter drainage away from the house, so what is the best way to install gutter downspout extensions? Well if you don't care about looks, you can run out to your nearest home improvement store and buy some cheap extensions that just lay on top of the soil and directs the water away. The biggest issues I see with this method are: 1. they get clogged easily 2. they get blown off by the water pressure in a hard rain -the time you need them the most! 3. you have to move them or go around them every time you mow 4. usually they are too short and don't direct the water far enough away from the foundation. My recommendation is to install underground downspout extensions at least ten feet away from the house. This will keep the drainage pipe out of the way, it will stay connected in a heavy rain, and if installed correctly with the correct materials, it will not clog up. Here is a video on the best type of pipe to use for a clog free system. https://youtu.be/7m_9gnoZD7A
Hopefully now you understand the importance of having good gutter drainage away from your foundation. If you live in a heavy rain area, I would strongly recommend you installing some underground gutter downspout extensions. Always remember, if you are unsure of how to handle your drainage issues properly, contact a local professional.