Improvising a drip edge on low-pitch polycarbonate roofing

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neb

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#295754 20-Apr-2022 19:09

One of the many features of the Casa de Cowboy is some low-pitch polycarbonate roofing over the front door, where the pitch is low enough that water backtracks up under the polycarbonate and drips down the fascia. In theory this could be handled by adding a drip edge under the polycarbonate, but I'm worried that poking that up under it will make the pitch even shallower and either exacerbate the existing issue or introduce new ones.

Another possibility that someone suggested is to unclip the guttering and run a bead of neutral-cure silicone under the edge of the polycarbonate, just back from the edge, so the water drips off that into the gutter before it can run all the way back to the fascia. This sounds like a far more workable solution, but before I end up being the next owner's cowboy I wanted to check whether anyone could see any problems with this, or had any better ideas.

jonherries

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#2904539 20-Apr-2022 19:25

That is what I have read too - the alternative is to change the edge profile to bullnose from the same source.

It reminds me I need to one of these for my pergola roof, although the overhang/soffit is wide enough/roof angle high enough to minimise most of it.

Jon

mdf

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#2904555 20-Apr-2022 20:06

Seems like a reasonable plan, but it will be a PITB to get neat. How visible is that section of the polycarbonate?

jonherries

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#2904557 20-Apr-2022 20:09

If you made a channel with masking tape it might look ok - not sure how raised it needs to be?

neb

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#2904561 20-Apr-2022 20:31

mdf:
Seems like a reasonable plan, but it will be a PITB to get neat. How visible is that section of the polycarbonate?

Pretty much non-visible, fascia to one side, gutter below and to the other side. That's why it'll require unclipping the guttering, it's completely screened by that. Here's a photo taken earlier in the year before the end-of-summer leaf clearout:

So the run of silicone would be 1-2cm in from the edge to ensure water drips down into the guttering rather than backtracking until it hits the fascia. Just need to make sure I use the appropriate neutral-cure silicone, some of the Sika ones at least are specifically advertised as being safe for polycarbonate.

Edited to add: Specifiically, Sikasil GP and Sikasil NG are the ones advertised for use with polycarbonate.

mattwnz

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#2904600 20-Apr-2022 23:00

I think the minimum pitch is about 3 degrees for corrugated and then you install an underflashing under it to redirect water back into gutter. Normally corrugated is also bent down at the ends in the troughs to create a better drip edge

Bung

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#2904608 20-Apr-2022 23:52

The minimum pitch for normal corrugated roofing is now 8°. When our low pitch roof was replaced it was with a rib profile that can go lower. The outer edge is translucent fibreglass as there's not a polycarbonate that matches the zincalume. If it was the metal edge it could be given a drip edge with a little fold. Water does run back a bit but only 20mm or so. It just leaves a dirty edge to the sheet above the gutter. I put FL2 gutters on to hide the edge.

It may be a trick of the photo but the roof at the Casa looks very low pitch and with the screws tightened it almost looks like the edge tilts up.

mattwnz

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#2904894 21-Apr-2022 16:10

The old style corrugated I understand can go down to 4 degrees, think they now call it true oak which has higher troughs and peaks. But there are other sheet profiles than can go down to 3%. Not sure what profile options there are from the translucent sheets, I recall there being a tray profile as we had one on a carport roof and that would have been installed with hardly any pitch. I don't recall there being a problem with it tracking back underneath it. Maybe it had a bead of silicon under it to create a drip edge, or they may have heated the front edge to then bend the front edge down.

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Jase2985

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#2904895 21-Apr-2022 16:12

some sort of clip on the edge of the roof in each trough to get it something that its more likely to drip off? similar concept to your bead of silicone but easier to install?

mattwnz

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#2905025 21-Apr-2022 17:19

I think if it is at the minimum 3 degree pitch for some profiles, that a 3 degree pitch shouldn't track back very far. So guessing that it hasn't been installed as per the minimum pitch requirements. But that is also one reason I understand an underflashing is often used too underneath the , providing a drip edge into the gutter, especially for higher wind zones. E2/AS1 should provide an acceptable solution

neb

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#2907061 26-Apr-2022 18:48

Got it sorted, at a fraction of the time and cost it would otherwise have taken, thanks to some advice from someone at M10. I was dreading have to take down the guttering since it's a long run and glued into the dropper which I'd all have to take down, so figured I could at least temporarily achieve the effect of the silicone drip line using that adhesive-backed water-barrier strip you can get for doors. So I asked a guy at M10 who wasn't wearing an M10 shirt but was helping people out, and he said what he does is get the cheapest polycarbonate roofing material they carry, cut it into strips, and push it up under the existing roof material to form a drip edge. Since it's barely-there thin, which is why it's the cheapest one they have, you can slot it in without having to loosen and tighten the roofing screws:

An impromptu watering-can test at various flow rates has indicated it'll do the job, just waiting for some serious rain to see if it holds up to that. So it looks like the entire problem is fixed for $16 and under an hour's work.

As an aside, when I described my original kludge fix to him, "just a temporary thing for now until I can do it properly", I actually threw up a little in my mouth as the words came out...