# Forum Home Renovation Roofing  Flat roof verandah leaking where polycarbonate sheets overlap

## slamdunk

Flat roof verandah leaking where polycarbonate sheets (corrugated profile) overlap. The fall is only 1 degree. Water seems to be seeping through bottom sheet. Silicone or flashing? Whats best to use to stop leaking? Which silicone or flashing to use? 
Appreciate any help.

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## stevoh741

For a start it needs to have a 5 degree fall for corro.

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## slamdunk

Yes I know but couldn't do it due to limited height.

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## stevoh741

you should be using trimdeck sheets for angles less than 5degrees. Not sure silicon will help your cause. How big is your sheet overlap?

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## r3nov8or

Even trimdek poly only goes to 3 degrees (trimdek steel to 2 degrees). You should use lockdek for 1 degree.

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## johnc

> Even trimdek poly only goes to 3 degrees (trimdek steel to 2 degrees). You should use lockdek for 1 degree.

  You may also have some water running back up the sheet a short distance from the low end with that small amount of fall..

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## Bedford

> You may also have some water running back up the sheet a short distance from the low end with that small amount of fall..

   Might have some coming up the top end too depending on how it's built.

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## watson

I have it on good authority ( Thank you David) that the regulation  SAA HB20-1997 (Soon to be reviewed by ASA) describes the correct solution.

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## Roofer

Polycarbonate Trimdek is still specified at 5°
88mm Per/m fall is very hard to achieve on most patios. 
My recommendation is to put more battens in maybe one in between your current battens. 
If you have batten spacing at around 400mm you will find that the sheet will not
sag and you will not get any leaks.

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## r3nov8or

> Polycarbonate Trimdek is still specified at 5°
> 88mm Per/m fall is very hard to achieve on most patios.

   In Ampelite -
Greca and Corrugated are 5°
5 Rib (Trimdek compatible) is 3° 
Ref Domestic Solasafe Polycarbonate

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## Roofer

Interesting. 
Laserlite still specify 5°   http://laserlite.com.au/sheetingprod..._Instrctns.pdf

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## markinoz

> Flat roof verandah leaking where polycarbonate sheets (corrugated profile) overlap. The fall is only 1 degree. Water seems to be seeping through bottom sheet. Silicone or flashing? Whats best to use to stop leaking? Which silicone or flashing to use? 
> Appreciate any help.

  fellas - lots of what he ought to have used, but he said he was stuck with corri and that's what's on there and can anything be done??? how about we find out a little more about the actual story. assuming the sheets are overlapped length-wise;
- is the water coming uphill and leaking beneath the join?
- is the overlap where there is a batten underneath?
- how wide is the overlap?
- could lap-seal tape or even thinner anti-noise tape be used between the sheets to prevent the miniscus effect?
- dumb question - have you used polycarb screws with the 10mm hole in the sheets and the fat washer?
let's see how we go

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## r3nov8or

Yeah, fair enough. 
Flashing would be more permanent than any 'soft' (degrading) product. 
If  the whole roof is poly this might look a bit strange from below (but silicone etc will also look messy), but  I'd think about getting a steel supplier to roll you some zincalum or  colorbond flashing to fit over and protect the joins, like this   
Fix it down at the centre ridge with standard roofing screws, doing your very best to hit the large hole that you should already have after using and removing the 'one shot' poly screws 
It MAY be enough to cover only onw or two ridges, but hard to tell. If I was to choose two ridges, it would be the left-hand two 
You could buy poly flashing but I think they only have ridge and facia profiles. It's also expensive last time I looked.

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