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I have a large, steep roof section (~400sqft) connected by a long ~20' valley. During heavy rainstorms, the majority of the draining water completely overshoots the gutter, landing near the foundation.

Water jumping the gutter Roofline

How can I fix this? I've heard of manufactured or home-brew L-shaped attachments, as alluded to in this similar post here, but they didn't go in to any detail about how they work or where to get them. This answer attempts to describe them, but I don't really understand how to build one, and I read about potential problems with snow.

I'm open to just about anything, bigger gutters, some kind of ground drainage to deal with the overshot water, etc.

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    Corner baffles are a standard feature around here. They're part of the system and not "home-brewed". neiltortorella.com/images/…
    – isherwood
    Jul 26, 2016 at 18:35
  • I live in Oregon we get a lot of rain the corner baffle works great we don't often get large amounts of snow so I cant say how well they would hold up but the baffles do and on nicer jobs they have tapered or scroll work and add to the over all look. +
    – Ed Beal
    Jul 26, 2016 at 19:02
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    Not really, Call your local gutter installer. They'd probably sell you some. You wouldn't want it much bigger, though. You'll end up tearing your gutter off. You can't contain all of nature, after all. :)
    – isherwood
    Jul 26, 2016 at 20:38
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    Too late for this, but: don't you just LOVE architects who come up with insane roofline combos like this? sad. Jul 27, 2016 at 15:33
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    @CarlWitthoft Reported quotes from Frank Lloyd Wright: "If the roof doesn’t leak, the architect hasn’t been creative enough." Another gem: "Move the table" - response to a client who phoned him to complain of rain leaking through the roof of the house onto the dining table. Jul 27, 2016 at 16:35

3 Answers 3

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I represented a company that installed roofs and gutters in NC for 4 years. Your gutters are way too far below the shingles. Judging from the pictures this looks like an older house and you may have some issues with how level the roof line is and perhaps that is why. Ideally, you want the gutters touching the shingles on the high end and sloping down gradually to the downspout but not more than an inch below the shingles. From the pictures, it looks like the water is missing the gutters entirely when it rains hard.

You have half round gutters, which tend to act as a "ski jump" if there is any velocity behind the water flow. The way to reduce this is to use a diverter which is vertical piece of metal bent into a "L" shape with the bottom section about 3/4" wide and the vertical part about 4" wide. It is screwed to the outer lip of the gutter. I don't know if you can buy them, our guys just made them from scrap pieces of gutter. They will trap snow and debris and you will want to clean behind them from time to time. The easiest way is with an old paint brush attached to one of those painters extension poles. enter image description here

I suggest getting a well qualified gutter company involved. You have half round gutters on open rafter tails which may require changing the brackets and there are a lot of different brackets to choose from. You will want someone who knows what they are doing. I doubt you will be able to eliminate the overshooting entirely, but you should be able to greatly reduce it so that in most storms it's fine.

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  • Any thoughts on supplemental mitigation at the ground level? If you look closely at the ground in my second photo, you can see I jury rigged some big plastic bin lids to channel the jumping water away from the foundation. Is there something a bit more elegant than this other than the obvious concrete rain diverter? Jul 27, 2016 at 16:37
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    The key to protecting your foundation is good slope away from the house. Even if you have to build up the grade next to the house. Any hard material that will not erode will work and I have seen all kinds of things. Rocks are the most obvious, but put something like heavy landscape plastic under them so the water doesn't saturate the ground and the rocks or whatever you use don't sink into the ground. If the slope can't be corrected for some reason, I have seen instances where people have put in large clay pots or decorative rain barrels with a overflow hose leading away from the house. Jul 29, 2016 at 2:21
  • Roofing/gutter guy said that the gutters can't be raised any further. He pointed out that the left side in the above picture is as high as it can go. He pointed out that the house is sinking on the left side of the photo, and in order to pitch the gutters to the downspout at the corner, the gutters have to drop off as they are. Aug 15, 2016 at 1:50
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Use wider 6" gutters. I'd also add gutters to the upper roof line that dumps onto that portion of the roof that is a problem area. This will help control water flow.

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  • Thanks, i would guess they may already be six inches wide. Also, the lens doesn't make this clear, but the dormer square footage is pretty insignificant, probably 50 sqft compared to at least 400. Jul 26, 2016 at 18:50
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    Those are 4 or 5" gutters. 6" is an uncommon size for residential applications.
    – isherwood
    Jul 26, 2016 at 20:38
  • @isherwood how do you measure? Is it the width or the depth? Jul 26, 2016 at 22:37
  • That dimension usually refers to the outer top horizontal measurement.
    – isherwood
    Jul 27, 2016 at 13:19
  • The gutters are already six inches. Aug 4, 2016 at 12:37
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I know this is an old post but your gutter installer should be strung up under those gutters during a hard rain. There should have been two downspouts, one at either end and the gutter should be right under the shingles at the inside corner sloping down to the two ends. Smdh

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