Shim material for rainscreen vent sv-3
In order to save some money on my project, I went with the sv-3 (7/16” thickness) instead of the sv-5 (3/4”) rainscreen vent by cor-a-vent even though I am using 3/4” plywood for my furring strips. The sv-3 is about $3.50 ea. While the sv-5 is about $8 ea.
That would really add up in cost so I thought I could still use the sv-3 and shim it out 5/16” to match the 3/4” plywood. Plus, I already have the sv-3 and probably can’t return it which is another reason I’m forced to get creative. Originally I was going to just use 1/2” plywood furring, but James hardie requires 3/4” furring and so that is what I am going to use for my project. That’s sort of how all of this came about…
my question is, what material would be a good option as a shim. And keep in mind the shim needs to be continuous or the bugscreen won’t have any effect.
What I thought might be good to use was strips of 5/16” hardiepanel that I can easily rip with my shears. I don’t see a problem with that but wanted to double check before using it.
also I will be pretty close to grade around the whole house – ranging from 3”-5” above grade.
buying a sheet of 5/16” plastic, or Azek would defeat the purpose in this, although it would be an ideal shim, I might as well just buy the sv-5.
am I ok to use the hardie for my shim? Or is there another option?
thanks again
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Replies
Kevin, the Hardi-panel will work fine. You probably want to make the strips about 3" wide to prevent cracking when you nail them. That's something you can experiment with.
Other alternatives are to rip strips off scrap 2"x dimension lumber you have left over.
Malcolm, thank you for your thoughts. I only thought to use the hardie instead of wood was because of the low grade (as also my water table trim board is also hardie). And yes I actually did rip them already to 3” but before priming cut edges and installing wanted to see if I was missing something.
Kevin,
This is how I did it in a similar situation. The first picture is of the rain-screen battens and perforated J flashing. The second shows the Hardi water-table and cap-flashing above.
Malcolm, do you know the hole size and hole spacing for the j channel?
Kevin,
Because all houses have to have rain-screens here, lumberyards alls stock the J channel in two or three widths, and can bend the perforated stock into others if requested.
Here is a link to a local supplier with similar products: https://www.menzies-metal.com/metal-flashings/perforated-j-channel-rain-screen-low-back/
Malcolm, I’m in the process of looking for some perf. J channel. Wondering how much to order for myself. Is it primarily necessary at the bottom of the wall where weeds, weedwhackers and majority of bugs and moisture will be, and not as needed above and below windows and at the top of the wall?
Can I get away with using j channel and bug screen just at the bottom and going with bug screen and no ‘j’ everywhere else venting is required.
Also, in the picture you attached showing the j, is there no bug screen on there? Is bug screen not used with it? I believe those are 1/8” holes by the way after some digging.
Kevin,
It is used as a combined pest and insect screen. The only thing I've heard of getting in past that flashing are small sugar-ants - and I've never found anything that will stop something that small.
We only screen at the bottom of the wall. Above windows and doors the cap-flashing takes its place. The trim above the flashing is set so that there is a just under 1/8" gap so bulk water can drain.
Ventilation for those cavities is provided by gaps in the battens above the windows so there is some air circulation. it's a good idea to keep the battens off the window flanges anyway. It avoids having to compensate for the thickness of the flange, makes taping the jambs easier - and imagine how easy it would be to replace the window if it was ever necessary.
We don't typically vent the top of the walls. Do they perform better vented? Sure, but without top venting you still get the vast majority of the benefits of a rain-screen. The experience here seems to be that cavities without top-venting are performing extremely well.
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