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I am about to replace my gutters, one guide I have read say the gutter should never be more then 30mm below the bottom of the roof tiles, another says 50mm.

What is the reason for this?

What is a safe distance?

(I want to get a good fall on the gutters and I expect that the bottom of my tiles are not level… I am planning to fit felt support tray at a later date)

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How far below the drip edge is the current gutter? Why can't you install the new gutter in the same place as the old one? –  Tester101 Jul 11 '12 at 15:06
    
@Tester101, the current gutter does not slope towards the outlets, so it overflows etc. –  Walker Jul 11 '12 at 15:53
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2 Answers

up vote 5 down vote accepted

3-5 centimeters is in the 2-3 inch range.

Any more and you run the risk of water running off the tile and overshooting the gutter.

The gap can vary some because the gutters must slope towards the downspout.

Edit post comments: When you install your new gutters, put the point furthest from the downspout at the highest possible point against the bottom of the roof, and then slope gradually down to your downspout. You're never going to hit the "maximum" that way.

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Thanks so the key is the distance between the front of my tiles and the far side of my gutter - easy to fix as I can push tiles back a bit if they overhead too match. –  Walker Jul 11 '12 at 13:14
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You should not push the tiles back beyond manufacturer recommendations because you need to make sure you have a proper drip edge. If you don't have that, water will collect at the end of the tile, wrap around and soak into the underlying surfaces that aren't supposed to get wet. –  The Evil Greebo Jul 11 '12 at 13:27
    
3" seems like a lot. If you start at 3", you'll be at 3 3/4" at the end of a 30' run. Depending on the slope of the roof, the water might cascade right over the gutter (but I'm no physics major, so I'm not sure how to calculate the path of falling water). –  Tester101 Jul 11 '12 at 15:04
    
@Tester101, You got it the wrong way round, 3" is the point away from the outlet, so it gets less closer to the outlet. –  Walker Jul 11 '12 at 15:55
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@Walker Huh? your gutters slope up towards the downspout, not down? You must have some odd water where you are, if it flows up hill. The 3" would be the distance measured from the drip edge (the point at which the water falls from the roof), to the top of the gutter. Since the gutters have to slope down towards the downspout, this distance will increase as you get closer to the downspout. –  Tester101 Jul 11 '12 at 16:01
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Start at the highest point with the back of the gutter as high as it will go (up against the bottom of the slate or tile or galvanised iron roof). Slope the gutter down form there towards the spout. If the run is long, you may need flashing to cover the exposed part of the facia. Water will blow in there, and rot the timber facia. Flashing will start from underneath the roof and bend down and overlap the back of the gutter.

Don't assume that the gutter is already sloping to the spout. Check it, get the slope right before installing brackets etc. Use a transparent plastic hose filled with water to check levels.

P.S. Some modern guttering has the back lower at the back than the front. Don't use it. When the gutter overflows, where do you think that the water will flow? Back to the house, and depending on the design of the house, water will find its way inside the exterior wall. If it doesn't do that, it time it will rot the facia.

In some modern houses in Sydney, overflow water found its way inside the exterior wall, rotting the timbers supporting the interior wall, floor timbers, and carpets.

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If you have more information either edit your answer or add a comment. –  ChrisF Jul 12 '13 at 7:52
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