Roofing overhang on Gutters

It depends on a lot of things, type of gutter how many downpipes and if the slope on the gutter is correct, I understand that 50mm is a good measure into the gutter if water is getting behind the gutter then the water is not getting out of the gutter quick enough down the downpipes and overflowing into the facia, maybe blockage, not enough downpipes, slope wrong etc
Lysaghts web have a chart to help with this http://www.lysaght.com/go/products-a...-roof-drainage.

There is only one downpipe at the end. I suspect the fall isn't enough, but the gutter was not overflowing. I was out in the rain, up a ladder watching it, and the gutter was not full, but somehow the water was getting behind the gutter and running down the fascia.

Depends on gutter design and the way was installed, but the shaped front of the gutter should sit slightly lower than the back flat edge. Often the back has been bent over or trimmed to allow fitting to the fall and in heavy rain the water flows back instead of over the front (or through the overflow drain slots in some gutter profiles). It is more to do with those issues than the distance into the gutter of the roofing.

If it is a persistent problem you can easily install a flashing piece of bent gal or zincalume (depends on what the roof & gutters are - pick the wrong one and you will get early corrosion) flat iron or other suitable flashing material that sits on top of the bottom batten and runs down and over the edge into the gutter. Sealed with a bead of roofing silicone between it and the back rise of the gutter.

In high rainfall areas it was once common to have relief holes in down-piping or guttering so that if they get over capacity the water simply flows out sideways then down onto the ground. Once the flow rate drops then gravity sends it down the pipe again. Don't see many of those now though.

In the olden days the design of roofs included what are called 'ponding boards', especially on lower pitched roofs and when there were narrow or no eaves (so any water going backwards would flow onto ceilings and down internal walls). These were a flat board laying almost a full tile depth up the roof from the barge board (about 300-400mm) and sheathed with gal flat iron or lead over into the gutter as I described above. No silicone in those days - many were fully soldered to the gutter, but commonly were sealed with pitch or bituminous mastic (tarry stuff). Meant that any water overflow would always flow away from the house.

I was getting water flowing behind my gutters and down the fascia board. It turned out my metal roof hadn't been turned down on the end of the sheets and water was lipping under the sheets and running back until it hit the fascia board.

Originally Posted by finger

I was getting water flowing behind my gutters and down the fascia board. It turned out my metal roof hadn't been turned down on the end of the sheets and water was lipping under the sheets and running back until it hit the fascia board.

I assume when you mean turned down, there should be a slight bend in the end of the sheet? If so, then this hasn't been done. Anyone know if it's standard practice to do this?

Perhaps this is a regional thing, but in my experience roofing steel of any type is not turned down into guttering. The ends are commonly turn up at ridges and at the high end of flat roofs mostly to stop wind driven rain getting in, but if there is the correct overhang in to a gutter that should not be an issue. Maybe some roofing plumbers might be able to give better opinion.

It was the roof plumber that did it for me, the only reason I noticed it worked was he missed a few spots along the roof and as soon as we got our first downpour the water was dripping down the fascia. I got up and finished the spots he missed and it stopped.

With that said he was a bit over zealous with the turn downs and tore the sheets to make a spout on each valley. I was pissed but by the time it rusts I'll need a new roof anyway. My roof pitch is 5 - 10 degrees at most.

Turn down depends on the type of sheet. It is done on deck but not on corrugated iron. If you have corrugated iron, the pitch of your roof may be below the minimum recommended by the manufacturer.


Tools

Yeah, my roof is nearly flat and it is CGI.

On the stratco site it states it under CGI Corrugated Installation Information.

http://www.stratco.com.au/Products/R...ugated/cgi.asp

With that said I was only going with the recommendations of the plumber who in the end turned out not to be the best.

What profile is the gutter? square or quad (round at front) either way the front is most likely higher than the back of the gutter, (hides the ends of the corro sheets better).
Different profiles have different carry capacity of water, another downpipe will certianlly help. In Qld they have slotted gutter (across the front) to allow for the monsoonal rainfall.