Rainscreen and insect screening
user-7292648
| Posted in General Questions on
In the 2013 GBA Rainscreen article, Martin Holladay wrote that using horizontal insect screening at the bottom and top of walls is not common anymore. Is that true, and if so, what is recommended now? We are using 1/4″ wood furring strips, so some of the thicker systems such as Cor-A-Vent seem like they would not work for this project. Thank you.
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Replies
User ...648,
Is there a reason you can't use thicker strips? 1/4" battens, even if made of plywood, will break easily, and the resulting cavity is so narrow that it is easily blocked or bridged by any wrinkles in your WRB, defeating the gap's purpose as a providing ventilation and a capillary break.
Here in BC, insect-screen was replaced by performed base flashing similar to this, which is much harder to damage: https://www.menzies-metal.com/vent-flashings/perforated-j-channel-rain-screen-low-back
Thank you. We are replacing the siding on a 1920s house, and we are trying to minimize how much further the new siding will come out. We are using Zip-R sheathing for our WRB, so there won't be any wrinkles. The J-channel looks great, but we're wondering if we need something that expensive. One thought was a corrugated lath strip wrapped with mesh screen as shown at the bottom of the picture:
https://www.mtidry.com/uploads/Lap-Siding-CLS.pdf
Thanks again.
That makes sense. The main problem with insect screen is mechanical damage when grass or other plants grows up into the bottom of the cavity, and can't be removed without damaging it. If you keep an eye of that you should be good.
With the recent popularity of open-joint cladding systems, the need for insect screening is coming up more often.
On the north side of my house, I mistakenly left the insect screening with my rainscreen system to complete after I had clad and so I never got to it. On the south side, I included insect screening top and bottom. Nearly 20 years later, NEITHER wall has any insects setting up shop in the ventilation space.
Some say so long as the space is dry, few insects want the space. Others say if some insects use the space, what does it matter, as long as they use the space without degrading it.
I am not sure I have the answer to these questions, but they are good ones.
Peter
Peter,
I think the answer depends on both climate and location.
A builder friend in rural Manitoba sent me pictures of the first rain-screen wall he built being opened up after several years. The whole cavity was clogged with the corpses of ladybugs.
My own experiences here in BC are that gaps in the insect protection allow spiders and wasps to nest - and leaving a path back to an inaccessible WRB for carpenter ants is asking for trouble.
Having once removed a seven foot long wasp nest from the soffits of a house, I can only imagine what could take up residence behind open-cladding.
Well I find wasp nests in inclosed areas of my own and client houses all the time.. the last time it was a football size bees nest, no big deal… and ladybugs, I’m not sure that’s scary enough? Bug Treatment is the help you need, that’s about all…!
Robert,
Anything, including the nests or corpses of insects, that builds up in the gap between the cladding and sheathing behind makes the rain-screen ineffective by impeding air-flow and bridging the capillary gap. Maybe that doesn't matter, but then why add a rain-screen in the first place?
Anyone know of a 3/4" thick bug screen product for top and bottom of ventilation channels? Using 1x vertical furring strips over 4" of foam board.
jjmc,
See post #1 above.
Cor-A-Vent SV5 is 3/4” thick and made to match up to 1x furring strips.
https://www.cor-a-vent.com/sv5.cfm