Rain screen needed for vertical metal siding?
Hello All! I’ve read through many posts about metal siding and the need for a rain screen product (like Cor-A-Vent or whatever) or not. One post indicated that code in BC is that if 8% or less of the siding material is touching the substrate, and has a drainage plane, that counts as a rain screen. Other posts say that vertically installed corrugated metal, as long as the bottom and top channels are perforated, is fine (corrugated seems like much higher than 8% touching).
We are looking at a vertically installed reverse board-and-batten type design, with only the fastener and locking strip touching, but it’s still more than 8% contact (maybe more like 15-20%). I’m still picking the exact product, but the depth of the siding might be as shallow as 3/8″ and as deep as 1″ — but definitely enough for good airflow and drainage. [I haven’t yet found a perforated channel that is wider than 3/4″ but the hunt continues].
We’d like to avoid adding a rain screen if it’s really not needed. Back-of-envelope calculation for Cor-A-Vent is like $10k in materials and labor (labor mostly, as we have a LOT of wall), and we are so far over budget it’s painful, so if it could be safely skipped, that would be great (safely being the operative word there).
Does anybody have any advice or concerns about skipping the formal rain screen and using perforated J/L channel for this type of siding?
Thanks so much!!!
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Replies
I think only our building official can answer the question. If they are OK with the reverse B&B, I would have no qualms about the extra bits touching the wall. Provided there is a perforated closure on the bottom, it will provide good drying path.
VTLiving,
The comments on BC, which were probably mine, were more concerned with code acceptance than practically whether it would work.
Like Akos I'd have no problems with what you are proposing - remembering that metal siding is impermeable, so a good vent path to remove moisture is important.
Hi Akos and Malcolm! Thanks for the speedy replies. We are in an area where there are no building codes, so that makes things either good or bad, or perhaps a bit of both, depending on ones perspective. So, no need to worry about code, we just want to make sure we're doing the right thing to let the sheathing dry if it needs to.
It's tricky to find a non-silver perforated bottom and top channel. I'm just finding silver for the most part, which will be visually obvious. Malcolm, I think you mentioned having a shop fabricate the top and bottom strips -- what type of shop would do this if I wanted to have something done in black instead of the silver?
Thanks again!!
VTLiving,
I'm fortunate in that the local lumberyard has a metal shop attached to it, so I get all my custom flashing from there. I would try a roofing supplier, or ask at your lumberyard for a recommendation.
Hi Malcolm. Thanks! I'll check to see what I can find. What thickness of metal sheet do you have them use?
VTLiving,
24 ga.
I've used this in a pinch, you might be able to find something equivalent locally:
https://www.homedepot.ca/product/alu-rex-basic-protection-20-ft-black-aluminum-gutter-guard/1001033236
You can also search for a local perforator company, they can make any sheet to your spec which you can used to bend up flashing.
Metal roofing suppliers also generally have something as it is used for vented ridge caps.
Thanks Akos, that was super helpful!!