# Forum Home Renovation Roofing  How far should the roof extend over the gutter?

## SlowMick

I have a lovely old bloke next door in his late 70's who has 12 x 7 m carport that was installed pre google earth. 
my problem is that is it is on the fence line and it has no gutters.  this means the rain runs of the roof and floods my garage next door. 
Over christmas I plan to cut back the tin on the roof to make sort of a straight line and put up some guttering but i was wondering - how far over the gutter is the tin supposed to sit?

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## plum

G'day SlowMick, 50mm should be enough

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## SlowMick

thanks heaps bloke.  have a good night.

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## Danny

It is a big carport and an 84 sq m roof will require (Melb 1:20 ARI) a 100mm round downpipe plumbed mid point and a gutter to suit. A 50mm overhang would then be ok as plum has suggested but are you able to trim the roof and fit a gutter within his boundary or are you limited to fitting a narrow gutter and 2 smaller downpipes at each end? It is best to have at least a 60mm access gap for maintenance and this would require a shorter overhang for a smaller gutter.

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## SlowMick

thanks for that Danny, sounds like this is much more invloved than i first thought. i will get out the tape measure and confirm the measrements of the carport. 
there should be enough room on his side of the fence for a gutter but i don't really care if it overhangs the fence - just sick of the shed getting flooded with all of this new found rain we are having in Melbourne now.

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## Danny

I mentioned the boundary more because of possible resale buyer leverage issues further down the track. I am also assuming that the 12 m side is where the gutter will be going. As the guttering is along the fence line, I hope he doesn't have a concrete driveway that you will have to dig up to connect to the stormwater.

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## Black Cat

Or you could be sneaky and have a heavy chain instead of a downpipe and have the rain running down that into ground able to absorb it ... There 's a rain water garden in the Tasmanian Botanical gardens that demonstrates ways of dissipating rainwater without it going out to sea.  http://www.rtbg.tas.gov.au/index.aspx?base=495

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## The Roofer

Just a few additions to the above:50mm overhang plus a 20mm downturn at 45 degrees.Danny is correct in working out downpipes etc and access to stormwater - great advice.Black Cat - love this as most of the rainwater today is being diverted to stormwater instead of groundwater (basins, water table etc) and if this is possible for Slow Mick it makes for great garden irrigation and a return to the old days where water tables were higher and slab cracking less common. There's also some new device available for overflowing gutters that Danny mentioned in an earlier thread (check with Danny) that could have the same outcome as the chains but instead of extra downpipes?

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## jatt

I'm guessing the pitch on that carport isnt very much so that 20 mm downturn at the end is a darn good idea. 
When possible I always run minimum 90 mm poly.   
If its gonna go around bends underground then an IO at some point to access a tee with a screw on cap.
Overkill.. maybe until you have to clean out the crap from trees that drop leaves into the gutter.

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## Danny

> When possible I always run minimum 90 mm poly.

  I assume you mean 90 mm UPVC.  
This size on a 12 metre length of gutter harvesting 84 sq m of roof would struggle to cope with anything greater than a Melbourne 1:20 ARI. Although not compliant for a 1:20 ARI for this roof area, it would cope if plumbed mid point but not if it was plumbed at the end of a 12 m run. 90 mm PVC however should never be buried as it is only 2 mm thick and not pressure rated but many people do (make this mistake). If DWV stormwater pipe is buried with the required minimum 1:100 fall, it should generate a sufficient flushing velocity during storm events.

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## SlowMick

i got up on the shed roof tonight and measured the car port.  i overstated it a bit.  the car port is 8 metres long (gutter side) and 6.7 metres wide.  The framing is 250mm so there is plenty of room for a gutter and down pipe on his side of the fence. 
Any chance you could do the calcs again for me Danny? 
Roofer, if the roof is corrugated how is the 20mm turn down achived?  big pair of pliers and do the corrugations one at a time? 
Unfortunately I down hill from my Neighbour Black Cat - i'm going to have to find the storm water for this one.  Currently the water run off the roof , over the fence and fills up gap between the fence and my garage - then it runs through the shed. 
Thank you for all the help guys.   :2thumbsup:

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## Danny

Hi SlowMick, 
You sound like a good neighbour. 
A 90mm round will be fine. How is it going to run to the stormwater?  
A (weakening) dose of rain heading our way, what part of Melbourne are you in? Mildura had 60mm in 2 hours earlier and Stawell was also hit hard. Got any sandbags?

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## SlowMick

Thanks for that Danny.  I'm out near the Dandenongs.  My family has always joked that when the Weather Bureau says the "showers clearing" the mean they are clearing off to the Dandenongs.  Don't mind few showers but figure the colorbond won't last long term. 
Do you think i could get away with a regular quad gutter?  the storm water easment runs under the car port so finding a pipe shouldn't be too hard - just a lot of digging  :Frown:

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## Danny

Aaah, practically neighbours! 
Quad should be fine. If you plumb the downpipe at the end, the 8 metre run might cause a problem during a torrential downpour as it would be a couple of metres longer than compliance. It would really depend on the fall.     
The device The Roofer mentioned earlier prevents gutters overflowing unless of course the gutters or downpipes are blocked. It is fitted at the guttering high point. For the recalculated 54 sq m roof, it could discharge 1.2 mm of rain a minute or an equivalent 72 mm of steady rain an hour. If worst came to the worst, I would send you one. It discharges through a 20 mm PVC pressure pipe that would normally drain at only 6 lpm and reconnects back into the existing downpipe, making it all very neat.

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