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)
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.
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.
My understanding is that if the gutters are placed too high that a sheet of snow could slide off and if it catches the front of the gutter it can tear it off. I read that the start of a gutter needs to be low enough that if you took a level and laid it on the roof it should clear the front edge of the gutter. This way any snow sliding off would clear the gutter and not damage it. My understanding is then a 1/16" per inch pitch is standard..
Gutters that are too high can enable runoff water to drip down their back side, which in turn can cause deteriorating fascia boards and stains on siding. Hanging gutters too high is a common mistake..
