Stopping Water Return on a Flat Roof

[Scooterscum]

Gidday.
My house has a flat corrugated (sp?) roof. Most of my facias have rotted due to the water running back under the tin overhang, and running down between the gutter and facia. Shortly i will be replacing both facias and gutters and would like some advice on how to stop/minimise this "runback" and directing it to the gutters.
I will be replacing the facias with treated pine (ie am not interested in using matal facias for various reasons that I will not go into here.
I have removed a section of gutter (oh o.k. - it fell off by itself!!) and have tried a couple of methods.
1. bending down the valley of the tin - it just tears.
2. Using a punch from above to make an "tit" to direct the water into gutter.
3. A bead of silicon along the bottom of the edge of the tin which works great but I'm not too sure how long the silicon will last, and once the gutter is up it will be very difficult to replace the silicon bead.
Any ideas??
Regards
Simon

[journeyman Mick]

Simon,
how about fixing a small metal angle (either c'bond or ally) under the front edge of the sheeting to act as a drip mould. This would have the same effect as your silicone bead but be longer lasting. Alternatively you can put a small snip in the corners of the pans (I'm assuming you've got trimdek or other flat profile) and bend the edge down, then fill the little corner nick with silicone.

Mick

[Gumby]

I've got exactly the same problem in one section of the roof where the colourbond only just overhangs the gutter and runs back under it. I bought some flashing and cut a length out, bent it to 90 degrees and slipped it under the colourbond roofing. The other face hanging down into the gutter. I then seasled it with some roof and gutter sealant and it's fixed the problem. I used a couple of tubes of sealant and applied a few 'coats' after each dried. Not pretty, but it can't be seen and as I said, I worked.

[Scooterscum]

Thanks for the reply Mick.
The roof tin is corrugated not flat profile - sorry I meant that the roof it self was flat ie minimal pitch.
If I run a piece of angle under the sheet edge only a small portion of it will touch the valley in the corrugation still allowing water to run past it during our (as you know!) tropical downpours.
I'll try snipping both sides of the corrugation before bending it down as you have suggested.
Thanks again for your advice.
Simon

[Gumby]

Thanks for the reply Mick.

If I run a piece of angle under the sheet edge only a small portion of it will touch the valley in the corrugation still allowing water to run past it during our (as you know!) tropical downpours.

If you put the flashing under far enough, it won't matter that it doesn't touch the roof shhet. The water will drip down onto the foil and run back down to the gutter. Use the silicon to help hold it in place.

[ozwinner]

I had the same problem at the shop premises we rent, the main roof is waaaaaaaaay too low an angle, and water would run back and drip inside.

I got the multigrips and bent the valleys of the tin, is that right " the valleys" anyhoo you get the picture.
Funny thing is, it only happens when it rains. :confused: ( waiting for Midges reply )


Al

[bitingmidge]

Funny thing is, it only happens when it rains. :confused: ( waiting for Midges reply )

OK so I guess it never stops happening!!!

Apart from that, for about the first time I can recall I actually disagree with Mick on something technical!!! DON'T snip the corners!!!

Eventually the silicone will fail and you will find the old osmotic thing happening down every snip! (I once spent $80,000 of an employers money fixing this very thing!)

There are a number of foam products which are designed to seal sheet roofing, "Compriband" is one brand. It comes in strips cut to match the profile of the roof, and is a compressable foam. Since you are removing the fascias, it shouldn't be a problem to take out the first row of fixings, lift the sheet slightly and slide in the foam. Screw through it and you have a permanent job!

If you have a flat roof and a corrogated profile, I'd guess that it's WAYYY to flat for the profile???

Bending down the valleys will help as well!

Cheers,

P

[ozwinner]

The only day of the year it rains, and we have to receive some welcome QLDers.

Sheesh.

Al

[journeyman Mick]

How flat is this roof anyway? Obviously too low a pitch for custom orb! :eek: First things first, go and find whoever built it like that and give them a good @rse kicking! It won't fix the problem but it'll make you feel better
Another fix for this (a bit bodgy but it's quick and will work) drive a small tek screw through every trough, right near the end of the sheet. This will act like a drip mould. The water is running back up the sheet because the surface tension is greater than the pull of gravity. The screw will draw the water down because both gravity and surface tension will be working for you.

Mick

[scooter]

You can reapply silicone to the underside of the valleys even when in place by squirting a dob onto your finger then scraping off against the end of the valley. Tedious but possible. To state the obvious, use a (neutral cure I think, best to check) type of silicone that is compatible with the gal, Roof & Gutter or somesuch.

Further to what Midge said, Diggers make a bitumen impregnated foam that is shaped to match a corrugated profile. Bunnings have it in the indoor timber section. Would be more a backup to bending and/or siliconing the valleys though I'd reckon.


Good luck.............cheers.........Sean

[Jacksin]

We have used a 'pole plate' flashing in the past to overcome this problem.

Basically it was a 50x50mm right angled flashing with a 45degree break back along one edge, which sat on top of the fascia with the 45deg bend uppermost (sorry I cant add a sketch) which stopped the water running or being blown back over the fascia.

Any roofing supplier will know what I am talking about.
Jack

[Scooterscum]

Thanks for all the advice guys - much appreciated.
Mick- the old fella who built the house is already dead so no satisfaction there! (mabey the previous owner had something to do about that ) I can't complain - we only paid a pittance for it so knew what we were getting into :eek:
I'll try Mick's tek screw idea first (because it sounds the easiest ) Failing that the flashing sounds like a good idea.
Thanks again for all the help and advice.
Regards
Simon