If you've just bought a new home and have witnessed a torrent of water running off your roof during rainstorms, you may be rather alarmed, especially if that never happened on any other home you've lived in. There's actually nothing wrong in the sense of something being broken, but there is something wrong in the sense that there's a huge mismatch happening between your roof pitch and your gutters. This is fixable, however; you just have to understand what's going on and why it's happening.
What Is Happening
Rainwater is running down your roof tiles, as it should, toward your roof gutters. But if you have valleys on your roof, where two sections meet and form a V, the water from both sections of the roof can run into the valley and combine into a stream. If the pitch of the valley is steep enough, the water can gather a lot of speed.
What Causes This
Think about what it's like to go down a waterslide. On shallow ones that don't have large hills or that don't have very fast streams of water in them, you tend to travel relatively slowly and drop into the pool at the bottom right by the slide. But on slides where there's a lot of water rushing down the slide plus a big hill, you shoot out of the end of the slide very quickly and tend to stay airborne for a bit longer, finally dropping into the pool farther away from the slide.
It's the same concept with water running down that valley on your roof. A steep valley and a lot of water combine to send the water shooting off the roof so that it misses the gutter. Normally gutters are sized to fit a roof's projected runoff so this doesn't happen, but it's very common to find gutters that are too narrow for steep roofs. So the combination of pitch, speed, gutter width, and potentially a slippery gutter guard that blocks water from entering the gutter can all contribute to the river of water falling off your roof.
What to Do
Initially, you should install a corner baffle in the gutter to block the water. Then, if you can, you should install a wider, over-sized gutter that can catch the water if it tries to over shoot. Keep the baffle installed in the new gutter, and ensure any gutter screens or guards have holes large enough to let fast-moving water in.
There is one more thing you have to do, and that's have a roofer check the state of the valley. With all that water running down, you have to be sure that nothing has worn away at the tiles. A roofer can also install flashing to protect the seam where the roof sections meet. Contact a professional roofing company, like Harrington & Company, for more information and help.