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Downpipes discharging water onto roof

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Our downpipes and guttering have been installed and I have some concerns about water being discharged directly onto the low-pitched roof, especially during heavy rain.


The rain from the gable roof (to the left) and the main roof where the solar panels are, which collectively are quite a large area of roof, is going to flow into the small length of guttering to the left of the dormer.  Then there's a small downpipe discharging from that gutter onto the low-pitched roof, close to the flashing and the rooflights.  And then down the downpipe to the left of the sliding doors.  I can see this causing us issues over time -  rain overflowing the small gutter to the left of the dormer, splashing on the render, leaks in our low-pitched roof and rooflights, potential overflow of the gutter at the bottom,  and damage and staining to the tiles where a lot of water is running over them.





I have so far come up with two options:


Option 1) Install the blue downpipe to take water directly from the gable roof down to the lower gutter.  Replace the small downpipe with a 45 degree pipe that connects into the vertical downpipe.  This would avoid the low-pitched roof entirely but it would look a bit unsightly.





Option 2) Don't install the downpipe from the gable.  Instead, run downpipe extenders on top of the pitched roofs to take the water directly from gutter to gutter. Like this: Should You Connect Gutters Between Floors? Gutters Guide (mygutterpro.com)


Are there any other solutions?





My second question:


Is it feasible for the existing downpipe to the left of the sliding doors to be moved to the far right hand side, so that I can tuck it away down the side of the house.  In other words, is it going to be OK for the water to go into the left hand end of that gutter, travel along the guttering over the sliding doors and then down the other side.  (Possibly a silly question but I'll ask it anyway!)



Edited by Selfbuildnewbie
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On your first question, I wouldn’t make any changes. All your roof tiling is at a sufficient pitch that this won’t cause any of the issues you are suggesting. If you render is silicone based, water will just run off it, you shouldn’t really get any staining. In fact, I can’t even see that the render is going to get wet, the discharge area is separated from the render by the flashing/membrane you have. Unless you went to the expense of designing in concealed gutters (which have their own problems) the guttering solution you’ve got installed already looks pretty standard to me.


 In the second question, yes, definitely move that to the opposite side of your sliding doors, very unsightly to have it there. You could even put in an angled drain piece to take it around the corner of the house and have it discharge 30cm away from the rear elevation so that you can’t even see it from your rear garden.

Edited by Adsibob
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We have several down pipes discharging onto pitched roofs. 


Instead of a straight down pipe I think it should terminate in a 45/135 bend that sends sideways at 45 degrees so that it runs down a wider area of the roof.



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On 19/04/2024 at 23:23, Selfbuildnewbie said:

potential overflow of the gutter at the bottom

Part H, Section 1 of the Building Regulations specifies how gutter sizes should be calculated so that they don't overflow in normal circumstances. Someone should have done those calculations.

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I think the gutter above the red X might overflow in heavy rain. Our roof also has lot of dormers which collect rain from a large roof area and concentrate it down towards a short section of gutter between them. Its not so much the size and number of down pipes that seems to cause the problem but heavy flows run down the tile quickly and overshoot the gutter. Perhaps check the gutter is far enough away from the house to minimise  how much water overshoots when its heavy. That said the occasional overflowing doesn't seem to create any problems for us.

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As Mike said this should have been calculated.

I would be more comfortable with your suggested option 1 as the roof to the ground floor section, which all the water is discharging onto, looks to have quite a low pitch, especially if it is a double lap plain tile like the main roof. Pitch and flashing type make me think it must be a single lap interlocking tile.

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